Chapter 24

RESULTS.

The foregoing study of illusions may not improbably have had a bewildering effect on the mind of the reader. To keep the mental eye, like the bodily eye, for any time intently fixed on one object is apt to produce a feeling of giddiness. And in the case of a subject like illusion, the effect is enormously increased by the disturbing character of the object looked at. Indeed, the first feeling produced by our survey of the wide field of illusory error might be expressed pretty accurately by the despondent cry of the poet--

"Alas! it is delusion all: The future cheats us from afar, Nor can we be what we recall, Nor dare we think on what we are."

It must be confessed that our study has tended to bring home to the mind the wide range of the illusory and unreal in our intellectual life. In sense-perception, in the introspection of the mind's own feelings, in the reading of others' feelings, in memory, and finally in belief, we have found a large field for illusory cognition. And while illusion has thus so great a depth in the individual mind, it has a no less striking breadth or extent in the collective human mind. No doubt its grosser forms manifest themselves most conspicuously in the undisciplined mind of the savage and the rustic; yet even the cultivated mind is by no means free from its control. In truth, most of the illusions illustrated in this work are such as can be shared in by all classes of mind.

In view of this wide far-reaching area of ascertained error, the mind naturally asks, What are the real limits of illusory cognition, and how can we be ever sure of having got beyond them? This question leads us on to philosophical problems of the greatest consequence, problems which can only be very lightly touched in this place. Before approaching these, let us look back a little more carefully and gather up our results, reflect on the method which we have been unconsciously adopting, and inquire how far this scientific mode of procedure will take us in determining what is the whole range of illusory cognition.

We have found an ingredient of illusion mixed up with all the popularly recognized forms of immediate knowledge. Yet this ingredient is not equally conspicuous in all cases. First of all, illusion varies very considerably in its degree of force and persistence. Thus, in general, a presentative illusion is more coercive than a representative; an apparent reality present to the mind is naturally felt to be more indubitable than one absent and only represented. On the other hand, a representative illusion is often more enduring than a presentative, that is to say, less easily found out. It is to be added that a good deal of illusion is only partial, there being throughout an under-current of rational consciousness, a gentle play of self-criticism, which keeps the error from developing into a perfect self-delusion. This remark applies not only to the innocent illusions of art, but also to many of our every-day illusions, both presentative and representative. In many cases, indeed, as, for example, in looking at a reflection in a mirror, the illusion is very imperfect, remaining in the nascent stage.

Again, a little attention to the facts here brought together will show that the proportion of illusory to real knowledge is far from being the same in each class of immediate or quasi-immediate cognition. Thus, with respect to the great distinction between presentative and representative knowledge, it is to be observed that, in so far as any act of cognition is, strictly speaking, presentative, it does not appear to admit of error. The illusions of perception are connected with the representative side of the process, and are numerous just because this is so extensive. On the other hand, in introspection, where the scope of independent representation is so limited, the amount of illusion is very inconsiderable, and may in practice be disregarded. So again, to take a narrower group of illusions, we find that in the recalling of distant events the proportion of error is vastly greater than in the recalling of near events.

So much as to the extent of illusion as brought to light by our preceding study. Let us now glance at the conclusions obtained respecting its nature and its causes.

_Causes of Illusion._

Looking at illusion as a whole, and abstracting from the differences of mental mechanism in the processes of perception, memory, etc., we may say that the _rationale_ or mode of genesis of illusion is very much the same throughout. Speaking broadly, one may describe all knowledge as a correspondence of representation with fact or experience, or as a stable condition of the representation which cannot be disturbed by new experiences. It does not matter, for our present purpose, whether the fact represented is supposed to be directly present, as in presentative cognition; or to be absent, either as something past or future, or finally as a "general fact," that is to say, the group of facts (past and future) embodied in a universal proposition.[147]

In general this accordance between our representations and facts is secured by the laws of our intellectual mechanism. It follows from the principles of association that our simple experiences, external and internal, will tend to reflect themselves in perception, memory, expectation, and general belief, in the very time-connections in which they actually occur. To put it briefly, facts which occur together will in general be represented together, and they will be the more perfectly co-represented in proportion to the frequency of this concurrence.

Illusion, as distinguished from correct knowledge, is, to put it broadly, deviation of representation from fact. This is due in part to limitations and defects in the intellectual mechanism itself, such as the imperfections of the activities of attention, discrimination, and comparison, in relation to what is present. Still more is it due to the control of our mental processes by association and habit. These forces, which are at the very root of intelligence, are also, in a sense, the originators of error. Through the accidents of our experience or the momentary condition of our reproductive power, representations get wrongly grouped with presentations and with one another; wrongly grouped, that is to say, according to a perfect or ideal standard, namely, that the grouping should always exactly agree with the order of experience as a whole, and the force of cohesion be proportionate to the number of the conjunctions of this experience.

This great source of error has been so abundantly illustrated under the head of Passive Illusions that I need not dwell on it further. It is plain that a passive error of perception, or of expectation, is due in general to a defective grouping of elements, to a grouping which answers, perhaps, to the run of the individual's actual experience, but not to a large and complete common experience.[148] Similarly, an illusory general belief is plainly a welding together of elements (here concepts, answering to innumerable representative images) in disagreement with the permanent connections of experience. Even a passive illusion of memory, in so far as it involves a rearrangement of successive representations, shows the same kind of defect.

In the second place, this incorrect grouping maybe due, not to defects in attention and discrimination, combined with insufficiently grounded association, but to the independent play of constructive imagination and the caprices of feeling. This is illustrated in what I have called Active Illusions, whether the excited perceptions and the hallucinations of sense, or the fanciful projections of memory or of expectation. Here we have a force directly opposed to that of experience. Active illusion arises, not through the imperfections of the intellectual mechanism, but through a palpable interference with this mechanism. It is a regrouping of elements which simulates the form of a suggestion by experience, but is, in reality, the outcome of the individual mind's extra-intellectual impulses.

We see, then, that, in spite of obvious differences in the form, the process in all kinds of immediate cognition is fundamentally identical. It is essentially a bringing together of elements, whether similar or dissimilar and associated by a link of contiguity, and a viewing of these as connected parts, of a whole; it is a process of synthesis. And illusion, in all its forms, is bad grouping or carelessly performed synthesis. This holds good even of the simplest kinds of error in which a presentative element is wrongly classed; and it holds good of those more conspicuous errors of perception, memory, expectation, and compound belief, in which representations connect themselves in an order not perfectly answering to the objective order.

This view of the nature and causes of illusion is clearly capable of being expressed in physical language. Bad grouping of psychical elements is equivalent to imperfect co-ordination of their physical, that is to say, nervous, conditions, imperfect in the evolutionist's sense, as not exactly according with external relations. So far as illusions of suggestion (passive illusions) are concerned, the error is connected with organized tendencies, due to a limited action of experience. On the other hand, illusions of preconception (active illusions) usually involve no such deeply fixed or permanent organic connections, but merely a temporary confluence of nerve-processes.[149] The nature of the physical process is best studied in the case of errors of sense-perception. Yet we may hypothetically argue that even in the case of the most complex errors, as those of memory and of belief, there is implied a deviation in the mode of connection of nervous structures (whether the connection be permanent or temporary) from the external order of facts.

And now we are in a position to see whether illusion is ultimately distinguishable from other modes of error, namely, those incident to conscious processes of reasoning. It must have been plain to an attentive reader throughout our exposition that, in spite of our provisional distinction, no sharp line can be drawn between much of what, on the surface, looks like immediate knowledge, and consciously derived or inferred knowledge. On its objective side, reasoning may be roughly defined as a conscious transition of mind from certain facts or relations of facts to other facts or relations recognized as similar. According to this definition, a fallacy would be a hasty, unwarranted transition to new cases not identical with the old. And a good part of immediate knowledge is fundamentally the same, only that here, through the exceptional force of association and habit, the transition is too rapid to be consciously recognized. Consequently, illusion becomes identified at bottom with fallacious inference: it may be briefly described as collapsed inference. Thus, illusory perception and expectation are plainly a hasty transition of mind from old to new, from past to present, conjunctions of experience.[150] And, as we have seen, an illusory general belief owes its existence to a coalescence of representations of known facts or connections with products of imagination which simulate the appearance of inferences from these facts.

In the case of memory, in so far as it is not aided by reasoning from present signs, there seems to be nothing like a movement of inference. It is evident, indeed, that memory is involved in and underlies every such transition of thought. Illusions of memory illustrate rather a process of wrong classing, that is to say, of wrongly identifying the present mental image with past fact, which is the initial step in all inference. In this way they closely resemble those slight errors of perception which are due to erroneous classing of sense-impressions. But since the intellectual process involved in assimilating mental elements is very similar to that implied in assimilating complex groups of such elements, we may say that even in these simple kinds of error there is something which resembles a wrong classing of relations, something, therefore, which approximates in character to a fallacy.

By help of this brief review of the nature and causes of illusion, we see that in general it may be spoken of as deviation of individual from common experience. This applies to passive illusion in so far as it follows from the accidents of individual experience, and it still more obviously applies to active illusion as due to the vagaries of individual feeling and constructive imagination. We might, perhaps, characterize all illusion as partial view, partial both in the sense of being incomplete, and in the other sense of being that to which the mind by its peculiar predispositions inclines. This being so, we may very roughly describe all illusion as abnormal. Just as hallucination, the most signal instance of illusion, is distinctly on the border-land of healthy and unhealthy mental life; just as dreams are in the direction of such unhealthy mental action; so the lesser illusions of memory and so on are abnormal in the sense that they imply a departure from a common typical mode of intellectual action.

It is plain, indeed, that this is the position we have been, taking up throughout our discussion of illusion. We have assumed that what is common and normal is true, or answers to what is objectively real. Thus, in dealing with errors of perception, we took for granted that the common percept--meaning by this what is permanent in the individual and the general experience--is at the same time the true percept. So in discussing the illusions of memory we estimated objective time by the judgment of the average man, free from individual bias, and apart from special circumstances favourable to error. Similarly, in the case of belief, true belief was held to be that which men in general, or in the long run, or on the average, hold true, as distinguished from what the individual under variable and accidental influences holds true. And even in the case of introspection we found that true cognition resolved itself into a consensus or agreement as to certain psychical facts.

_Criterion of Illusion._

Now, it behoves us here to examine this assumption, with the view of seeing how far it is perfectly sound. For it may be that what is commonly held true does not in all cases strictly answer to the real, in which case our idea of illusion would have to be extended so as to include certain common beliefs. This question was partly opened up at the close of the last chapter. It will be found that the full discussion of it carries us beyond the scientific point of view altogether. For the present, however, let us see what can be said about it from that standpoint of positive science to which we have hitherto been keeping.

Now, if by common be meant what has been shared by all minds or the majority of minds up to a particular time, a moment's inspection of the process of correcting illusion will show that science assumes the possibility of a common illusion. In the history of discovery, the first assault on an error was the setting up of the individual against the society. The men who first dared to say that the sun did not move round the earth found to their cost what it was to fly in the face of a common, though illusory, perception of the senses.[151]

If, however, by common be understood what is permanently and unshakably held true by men in proportion as their minds become enlightened, then science certainly does assume the truth of common perception and belief. Thus, the progress of the physical sciences may be described as a movement towards a new, higher, and more stable consensus of ideas and beliefs. In point of fact, the truths accepted by men of science already form a body of common belief for those who are supposed by all to have the means of testing the value of their convictions. And the same applies to the successive improvements in the conceptions of the moral sciences, for example, history and psychology. Indeed, the very meaning of science appears to be a body of common cognition to which all minds converge in proportion to their capabilities and opportunities of studying the particular subject-matter concerned.

Not only so, from a strictly scientific point of view it might seem possible to prove that common cognition, as defined above, must in general be true cognition. I refer here to the now familiar method of the evolutionist.

According to this doctrine, which is a scientific method in so far as it investigates the historical developments of mind or the order of mental phenomena in time, cognition may be viewed as a part of the result of the interaction of external agencies and the organism, as an incident of the great process of adaptation, physical and psychical, of organism to environment. In thus looking at cognition, the evolutionist is making the assumption which all science makes, namely, that correct views are correspondences between internal (mental) relations and external (physical) relations, incorrect views disagreements between these relations. From this point of view he may proceed to argue that the intellectual processes must tend to conform to external facts. All correspondence, he tells us, means fitness to external conditions and practical efficiency, all want of correspondence practical incompetence. Consequently, those individuals in whom the correspondence was more complete and exact would have an advantage in the struggle for existence and so tend to be preserved. In this way the process of natural selection, by separately adjusting individual representations to actualities, would make them converge towards a common meeting-point or social standard of true cognition. That is to say, by eliminating or at least greatly circumscribing the region of individual illusion, natural selection would exclude the possibility of a persistent common illusion.

Not only so, the evolutionist may say that this coincidence between common beliefs and true beliefs would be furthered by social as well as individual competition. A community has an advantage in the struggle with other communities when it is distinguished by the presence of the conditions of effective co-operation, such as mutual confidence. Among these conditions a body of true knowledge seems to be of the first importance, since conjoint action always presupposes common beliefs, and, to be effective action, implies that these beliefs are correct. Consequently, it may be argued, the forces at work in the action of man on man, of society on the individual, in the way of assimilating belief, must tend, in the long run, to bring about a coincidence between representations and facts. Thus, in another way, natural selection would help to adjust our ideas to realities, and to exclude the possibility of anything like a permanent common error.

Yet once more, according to Mr. Herbert Spencer, the tendency to agreement between our ideas and the environment would be aided by what he calls the direct process of adaptation. The exercise of a function tends to the development of that function. Thus, our acts of perception must become more exact by mere repetition. So, too, the representations and concepts growing out of perceptions must tend to approximate to external facts by the direct action of the environment on our physical and psychical organism; for external relations which are permanent will, in the long run, stamp themselves on our nervous and mental structure more deeply and indelibly than relations which are variable and accidental.

It would seem, from all this, that so long as we are keeping to the scientific point of view, that is to say, taking for granted that there is something objectively real answering to our perceptions and conceptions, the question of the possibility of a universal or (permanently) common illusion does not arise. Yet a little more reflection will show us that it may arise in a way. So far as the logical sufficiency of the social consensus or common belief is accepted as scientifically proved, it is open to suspicion on strictly scientific grounds. The evolutionist's proof involves one or two assumptions which are not exactly true.

In the first place, it is not strictly correct to say that all illusion involves a practical unfitness to circumstances. At the close of our investigation of particular groups of illusion, for example, those of perception and memory, it was pointed out that many of the errors reviewed were practically harmless, being either momentary and evanescent, or of such a character as not to lead to injurious action. And now, by glancing back over the field of illusion as a whole, we may see the same thing. The day-dreams in which some people are apt to indulge respecting the remote future have little effect on their conduct. So, too, a man's general view of the world is often unrelated to his daily habits of life. It seems to matter exceedingly little, in general, whether a person take up the geocentric or the heliocentric conception of the cosmic structure, or even whether he adopt an optimistic or pessimistic view of life and its capabilities.

So inadequate, indeed, does the agency of natural selection seem to be to eliminate illusion, that it may even be asked whether its tendency may not be sometimes to harden and fix rather than to dissolve and dissipate illusory ideas and beliefs. It will at once occur to the reader that the illusion of self-esteem, discussed in the last chapter, may have been highly useful as subserving individual self-preservation. In a similar way, it has been suggested by Schopenhauer that the illusion of the lover owes its force and historical persistence to its paramount utility for the preservation of the species. And to pass from a recurring individual to a permanently common belief, it is maintained by the same pessimist and his followers that what they regard as the illusion of optimism, namely, the idea that human life as a whole is good, grows out of the individual's irrational love of life, which is only the same instinctive impulse of self-preservation appearing as conscious desire. Once more, it has been suggested that the belief in free-will, even if illusory, would be preserved by the process of evolution, owing to its paramount utility in certain stages of moral development. All this seems to show at least the possibility of a kind of illusion which would tend to perpetuate itself, and to appear as a permanent common belief.

Now, so far as this is the case, so far as illusion is useful or only harmless, natural selection cannot, it is plain, be counted on to weed it out, keeping it within the narrow limits of the exceptional and individual. Natural selection gets rid of what is harmful only, and is indifferent to what is practically harmless.

It may, however, still be said that the process of direct adaptation must tend to establish such a consensus of true belief. Now, I do not wish for a moment to dispute that the growth of intelligence by the continual exercise of its functions tends to such a consensus: this is assumed to be the case by everybody. What I want to point out is that there is no scientific proof of this position.

The correspondence of internal to external relations is obviously limited by the modes of action of the environment on the organism, consequently by the structure of the organism itself. Scientific men are familiar with the idea that there may be forces in the environment which are practically inoperative on the organism, there being no corresponding mode of sensibility. And even if it be said that our present knowledge of the material world, including the doctrine of the conservation of energy, enables us to assert that there is no mode of force wholly unknown to us, it can still be contended that the environment may, for aught we know, be vastly more than the forces of which, owing to the nature of our organism, we know it to be composed. In short, since, on the evolution theory viewed as a scientific doctrine, the real external world does not directly mirror itself in our minds, but only indirectly brings our perceptions and representations into adjustment by bringing into adjustment the nervous organism with which they are somehow connected, it is plain that we cannot be certain of adequately apprehending the external reality which is here assumed to exist.

Science, then, cannot prove, but must assume the coincidence between permanent common intuitions and objective reality. To raise the question whether this coincidence is perfect or imperfect, whether all common intuitions known to be persistent are true or whether there are any that are illusory, is to pass beyond the scientific point of view to another, namely, the philosophic. Thus, our study of illusion naturally carries us on from scientific to philosophic reflection. Let me try to make this still more clear.

_Transition to Philosophic View._

All science makes certain assumptions which it never examines. Thus, the physicist assumes that when we experience a sensation we are acted on by some pre-existing external object which is the cause, or at least one condition, of the sensation. While resolving the secondary qualities of light, sound, etc., into modes of motion, while representing the object very differently from the unscientific mind, he agrees with this in holding to the reality of something external, regarding this as antecedent to and therefore as independent of the particular mind which receives the sense-impression. Again, he assumes the uniformity of nature, the universality of the causal relation, and so on.

Similarly, the modern psychologist, when confining himself within the limits of positive science, and treating mind phenomenally or empirically, or, in other words, tracing the order of mental states in time and assigning their conditions, takes for granted much the same as physical science does. Thus, as our foregoing analysis of perception shows, he assumes that there is an external cause of our sensations, that there are material bodies in space, which act on our sense-organs and so serve as the condition of our sense-impressions. More than this, he regards, in the way that has been illustrated in this work, the percept itself, in so far as it is a process in time, as the normal result of the action of such external agents on our nerve-structures, in other words, as the effect of such action in the case of the healthy and perfect nervous organism with the average organized dispositions, physical and psychical; in which case he supposes the percept to correspond, in certain respects at least, with the external cause as made known by physical science. And, on the other hand, he looks on a false or illusory percept as arising in another way not involving, as its condition, the pre-existence of a corresponding material body or physical agent. And in this view of perception, as of other mental phenomena, the psychologist clearly takes for granted the principle that all mental events conform to the law of causation. Further, he assumes that the individual mind is somehow, in a way which it is not his province to inquire into, one and the same throughout, and so on.

The doctrine of evolution, too, in so far as scientific--that is, aiming at giving an account of the historical and pre-historical developments of the collective mind in time--agrees with psychology in making like assumptions. Thus, it conceives an external agency (the environment) as the cause of our common sensations and perceptions. That is to say, it represents the external world as somehow antecedent to, and so apparently independent of, the perceptions which are adjusted to it. And all this shows that science, while removed from vulgar unenlightened opinion, takes sides with popular thought in assuming the truth of certain fundamental ideas or so-called intuitive beliefs, into the exact meaning of which it does not inquire.

When the meaning of these assumptions is investigated, we pass out of the scientific into the philosophic domain. Philosophy has to critically investigate the data of popular thought and of science. It has to discover exactly what is implied in these fundamental principles. Then it has to test their value by erecting a final criterion of truth, by probing the structure of cognition to the bottom, and determining the proper organ of certain or accurate knowledge; or, to put it another way, it has to examine what is meant by reality, whether there is anything real independently of the mind, and if so, what. In doing this it inquires not only what common sense means by its object-world clothed in its variegated garment of secondary qualities, its beauty, and so on, but also what physical science means by its cosmic mechanism of sensible and extra-sensible matter in motion: whether there is any kind of objective reality belonging to the latter which does not also belong to the former; and how the two worlds are related one to another. That is to say, he asks whether the bodies in space assumed to exist by the physicist as the antecedent conditions of particular sensations and percepts are independent of mind and perception generally.[152]

In doing all this, philosophy is theoretically free to upset as much of popular belief of the persistent kind as it likes. Nor can science find fault with it so long as it keeps to its own sphere, and does not directly contradict any truth which science, by the methods proper to it, is able to establish. Thus, for example, if philosophy finds that there is nothing real independently of mind, science will be satisfied so long as it finds a meaning for its assumed entities, such as space, external things, and physical causes.[153]

The student of philosophy need not be told that these imposing-looking problems respecting cognition, making, up what the Germans call the "Theory of Cognition," and the cognate problem respecting the nature of reality, are still a long way from being settled. To-day, as in the days of Plato and Aristotle, are argued, in slightly altered forms, the vexed questions, What is true cognition? Is it a mere efflux from sensation, a passive conformity of representation to sensation (sensualism or empiricism)? or is it, on the other hand, a construction of active thought, involving certain necessary forms of intelligence (rationalism or intuitivism)?

Again, how are we to shape to ourselves real objective existence? Is it something wholly independent of the mind (realism)? and if so, is this known to be what we--meaning here common people and men of science alike--represent it as being (natural realism), or something different (transfigured realism)? Or is it, on the contrary, something involving mind (idealism)? and if so, is it a strictly phenomenal distinction within our conscious experience (empirical idealism, phenomenalism), or one of the two poles of subject and object constituted by every act of thought (rational idealism)? These are some of the questions in philosophy which still await their final answer.

Philosophy being thus still a question and not a solution, we need not here trouble ourselves about its problems further than to remark on their close connection with our special subject, the study of illusion.

Our brief reference to some of the principal inquiries of philosophy shows that it tends to throw doubt on things which the unreflecting popular mind holds to be indubitable. Different schools of philosophy have shown themselves unequally concerned about these so-called intuitive certainties. In general it may be said that philosophy, though, as I have remarked, theoretically free to set up its own standard of certainty, has in practice endeavoured to give a meaning to, and to find a justification for the assumptions or first principles of science. On the other hand, it has not hesitated, when occasion required, to make very light of the intuitive beliefs of the popular mind as interpreted by itself. Thus, rationalists of the Platonic type have not shrunk from pronouncing individual impressions and objects illusory, an assertion which certainly seems to be opposed to the assumptions of common sense, if not to those of science. On the other hand, the modern empirical or association school is quite ready to declare that the vulgar belief in an external world, so far as it represents this as independent of mind,[154] is an illusion; that the so-called necessary beliefs respecting identity, uniformity, causation, etc., are not, strictly speaking, necessary; and so on. And in these ways it certainly seems to come into conflict with popular convictions, or intuitive certainties, as they present themselves to the unreflecting intelligence.

Philosophy seems, then, to be a continuation of that process of detecting illusion with which science in part concerns itself. Indeed, it is evident that our special study has a very close connection with the philosophic inquiry. What philosophy wants is something intuitively certain as its starting-point, some _point d'appui_ for its construction. The errors incident to the process of reasoning do not greatly trouble it, since these can, in general, be guarded against by the rules of logic. But error in the midst of what, on the face of it, looks like intuitive knowledge naturally raises the question, Is there any kind of absolutely certain cognition, any organ for the accurate perception of truth? And this intimate relation between the scientific and the philosophic consideration of illusion is abundantly illustrated in the history of philosophy. The errors of sense, appearing in a region which to the vulgar seems so indubitable, have again and again set men thinking on the question, "What is the whole range of illusion? Is perception, as popularly understood, after all, a big hallucination? Is our life a dream?"[155]

On the other hand, if our study of the wide range of illusion is fitted to induce that temper of mind which is said to be the beginning of philosophy, that attitude of universal doubt expressed by Descartes in his famous maxim, _De omnibus dubitandum_, a consideration of the process of correction is fitted to lead the mind on to the determination of the conditions of accurate knowledge. It is evident, indeed, that the very conception of an illusion implies a criterion of certainty: to call a thing illusory, is to judge it by reference to some accepted standard of truth.

The mental processes involved in detecting, resisting, and overcoming illusion, are a very interesting subject for the psychologist, though we have not space here to investigate them fully. Turning to presentative, and more particularly sense-illusions, we find that the detection of an illusion takes place now by an appeal from one sense to another, for example, from sight to touch, by way of verification;[156] now (as in Myer's experiment) by a reference from sense and presentation altogether to representation or remembered experience and a process of reasoning; and now, (as in the illusions of art) conversely, by a transition of mind from what is suggested to the actual sense-impression of the moment. In the sphere of memory, again, illusion is determined, as such, now by attending more carefully to the contents of memory, now by a process of reasoning from some presentative cognition. Finally, errors in our comprehensive general representations of things are known to be such partly by reasoning from other conceptions, and partly by a continual process of reduction of representation to presentation, the general to the particular. I may add that the correction of illusion by an act of reflection and reasoning, which brings the part into consistent relation with the whole of experience, includes throughout the comparison of the individual with the collective or social experience.[157]

We may, perhaps, roughly summarize these operations by saying that they consist in the control of the lower automatic processes (association or suggestion) by the higher activities of conscious will. This activity of will takes the form now of an effort of attention to what is directly present to the mind (sense-impression, internal feeling, mnemonic image, etc.), now of conscious reflection, judgment, and reasoning, by which the error is brought into relation to our experience as a whole, individual and collective.

It is for the philosopher to investigate the inmost nature of these operations as they exhibit themselves in our every-day individual experience, and in the large intellectual movements of history. In no better way can he arrive at what common sense and science regard as certain cognition, at the kinds of knowledge on which they are wont to rely most unhesitatingly.

There is one other relation of our subject to philosophic problems which I have purposely left for final consideration. Our study has consisted mainly in the psychological analysis of illusions supposed to be known or capable of being known as such. Now, the modern association school professes to be able to resolve some of the so-called intuitions of common sense into elements exactly similar to those into which we have here been resolving what are acknowledged by all as illusions. This fact would seem to point to a close connection between the scientific study of illusion and the particular view of these fundamental intuitions taken by one philosophic school. In order to see whether there is really this connection, we must reflect a little further on the nature of the method which we have been pursuing.

I have already had occasion to rise the expression "scientific psychology," or psychology as a positive science, and the meaning of this expression must now be more carefully considered. As a positive science, psychology is limited to the function of analyzing mental states, and of tracing their origin in previous and more simple mental states. It has, strictly speaking, nothing to do with the question of the legitimacy or validity of any mental act.

Take a percept, for example. Psychology can trace its parentage in sensation, the mode in which it has come by its contents in the laws of association. But by common consent, a percept implies a presentative apprehension of an object now present to sense. Is this valid or illusory? This question psychology, as science, does not attempt to answer. It would not, I conceive, answer it even if it were able to make out that the whole mental content in the percept can be traced back to elementary sensations and their combinations. For the fact that in the chemistry of mind elements may combine in perfectly new forms does not disprove that the forms thus arising, whether sentiments or quasi-cognitions, are invalid. Much less can psychology dispute the validity of a percept if it cannot be sure that the mind adds nothing to sensation and its grouping; that in the genesis of the perceptive state, with its intuition of something external and now present as object, nothing like a form of intelligence is superimposed on the elements of sensation, giving to the result of their coalescence the particular unity which we find. Whether psychology as a positive science can ever be sure of this: whether, that is to say, it can answer the question, "How do we come by the idea of object?" without assuming some particular philosophic or extra-scientific theory respecting the ultimate nature of mind, is a point which I purposely leave open.

I would contend, then, that the psychologist, in tracing the genesis of the percept out of previous mental experiences, no more settles the question, What is the object of perception? than the physicist settles it in referring the sense-impression (and so the percept) to a present material agent as its condition.

The same applies to our idea of self. I may discover the concrete experiences which supply the filling in of the idea, and yet not settle the question, Does intelligence add anything in the construction of the form of this idea? and still less settle the question whether there is any real unity answering to the idea.

If this is a correct distinction, if psychology, as science, does not determine questions of validity or objective meaning but only of genesis, if it looks at mental states in relation only to their temporal and causal concomitants and not to their objects, it must follow that our preceding analysis of illusion involves no particular philosophic theory as to the nature of intelligence, but, so far as accurate, consists of scientific facts which all philosophic theories of intelligence must alike be prepared to accept. And I have little doubt that each of the two great opposed doctrines, the intuitive and the associational, would claim to be in a position to take up these facts into its particular theory, and to view them in its own way.

But in addition to this scientific psychology, there is another so-called psychology, which is, strictly speaking, philosophic. This, I need hardly say, is the association philosophy. It proceeds by analyzing certain cognitions and sentiments into their elements, and straightway declaring that they mean nothing more than these. That is to say, the associationist passes from genesis to validity, from the history of a conscious state to its objective meaning. Thus, from showing that an intuitive belief, say that in causation, is not original (in the individual or at least in the race), it goes on to assert that it is not a valid immediate cognition at all. Now, I am not concerned here to inquire into the logical value of this transition, but simply to point out that it is extra-scientific and distinctly philosophic. If logically justifiable, it is so because of some plainly _philosophic_ assumption, as that made by Hume, namely, that all ideas not derived from impressions are to this extent fictitious or illusory.

And now we are in a position to understand the bearing of our scientific analysis of acknowledged illusions on the associationist's treatment of the alleged illusions of common sense. There is no doubt, I think, that some of the so-called intuitions of common sense have points of analogy to acknowledged illusions. For example, the conviction in the act of perception that something external to the mind and independent of it exists, has a certain superficial resemblance to an hallucination of sense; and moreover, the associationist seeks to explain it by means of these very processes which underlie what is recognized by all as sense-illusion.[158] Again, it may be said that our notions of force and of a causal nexus in the physical world imply the idea of conscious energy as known through our muscular sensations, and so have a suspicious resemblance to those anthropomorphic illusions of which I have spoken under Illusions of Insight. Once more, the consciousness of freedom may, as I have suggested, be viewed as analogous in its form and its mode of origin to illusions of introspection. As a last example, it may be said that the mind's certain conviction of the innateness of some of its ideas resembles those illusions of memory which arise through an inability to think ourselves back into a remote past having a type of consciousness widely unlike that of the present.

But now, mark the difference. In our scientific analysis of popularly known illusions, we had something by which to determine the illusory character of the presentation or belief. We had a popularly or scientifically accepted standard of certainty, by a reference to which we might test the particular _soi-disant_ cognition. But in the case of these fundamental beliefs we have no such criterion, except we adopt some particular philosophic theory, say that of the associationist himself. Hence this similarity in structure and origin cannot in itself be said to amount to a proof of equality of logical or objective value. Here again it must be remarked that origin, does not carry validity or invalidity with it.[159]

We thus come back to our starting-point. While there are close relations, psychological and logical, between the scientific study of the ascertained facts of illusion and the philosophic determination of what is illusory in knowledge as a whole, the two domains must be clearly distinguished. On purely scientific ground we cannot answer the question, "How far does illusion extend?" The solution of this question must be handed over to the philosopher, as one aspect of his problem of cognition.

One or two remarks may, perhaps, be hazarded in concluding this account of the relation of the scientific to the philosophic problem of illusion. Science, as we have seen, takes its stand on a stable consensus, a body of commonly accepted belief. And this being so, it would seem to follow, that so far as she is allowed to interest herself in philosophic questions, she will naturally be disposed to ask, What beliefs are shared in by all minds, so far as normal and developed? In other words, she will be inclined to look at universality as the main thing to be determined in the region of philosophic inquiry. The metaphysical sceptic, fond of daring exploits, may break up as many accepted ideas as he likes into illusory _débris_, provided only he has some bit of reality left to take his stand on. Meanwhile, the scientific mind, here agreeing with the practical mind, will ask, "Will the beliefs thus said to be capable of being shown to be illusory ever cease to exercise their hold on men's minds, including that of the iconoclast himself? Is the mode of demonstration of such a kind as to be likely ever to materially weaken the common-sense 'intuition'?"

This question would seem to be most directly answerable by an appeal to individual testimony. Viewed in this light, it is a question for the present, for some few already allege that in their case philosophic reasonings exercise an appreciable effect on these beliefs. And so far as this is so, the man of scientific temper will feel that there is a question for him.

It is evident, however, that the question of the persistence of these fundamental beliefs is much more one for the future than for the present. The correction of a clearly detected illusion is, as I have more than once remarked, a slow process. An illusion such as the apparent movement of the sun will persist as a partially developed error long after it has been convicted. And it may be that the fundamental beliefs here referred to, even if presumably illusory, are destined to exercise their spell for long ages yet.

Whether this will be the case or not, whether these intuitive beliefs are destined slowly to decay and be dissolved as time rolls on, or whether they will retain an eternal youth, is a question which we of to-day seem, on a first view of the matter, to have no way of answering which does not assume the very point in question--the truth or falsity of the belief. This much may, however, be said. The associationist who resolves these erroneous intuitions into the play of association, admits that the forces at work generating and consolidating the illusory belief are constant and permanent forces, and such as are not likely to be less effective in the future than they have been in the past. Thus, he teaches that the intuition of the single object in the act of perception owes its strength to "inseparable association," according to which law the ideas of the separate "possibilities of sensation," which are all we know of the object, coalesce in the shape of an idea of a single uniting substance. He adds, perhaps, that heredity has tended, and will still tend, to fix the habit of thus transforming an actual multiplicity into an imaginary unity. And in thus arguing, he is allowing that the illusion is one which, to say the least of it, it will always be exceedingly difficult for reason to dislodge.

In view of this uncertainty, and of the possibility, if not the probability, of these beliefs remaining as they have remained, at least approximately universal, the man of science will probably be disposed to hold himself indifferently to the question. He will be inclined to say, "What does it matter whether you call such an apparently permanent belief the correlative of a reality or an illusion? Does it make any practical difference whether a universal 'intuition,' of which we cannot rid ourselves, be described as a uniformly recurring fiction of the imagination, or an integral constitutive factor of intelligence? And, in considering the historical aspect of the question, does it not come to much the same thing whether such permanent mental products be spoken of as the attenuated forms or ghostly survivals of more substantial primitive illusions (for example, anthropomorphic representations of material objects, 'animistic' representations of mind and personality), or as the slowly perfected results of intellectual evolution?"

This attitude of the scientific mind towards philosophic problems will be confirmed when it is seen that those who seek to resolve stable common convictions into illusions are forced, by their very mode of demonstration, to allow these intuitions a measure of validity. Thus, the ideas of the unity and externality attributed to the object in the act of perception are said by the associationist to answer to a matter of fact, namely, the permanent coexistence of certain possibilities of sensation, and the dependence of the single sensations of the individual on the presence of the most permanent of these possibilities, namely, those of the active or muscular and passive sensations of touch, which are, moreover, by far the most constant for all minds. Similarly, the idea of a necessary connection between cause and effect, even if illusory in so far as it expresses an _objective_ necessity, is allowed to be true as an expression of that uniformity of our experience which all scientific progress tends to illustrate more and more distinctly. And even the idea of a permanent self, as distinct from particular fugitive feelings, is admitted by the associationist to be correct in so far as it expresses the fact that mind is "a series of feelings which is aware of itself as past and future." In short, these "illusory intuitions," by the showing of those who affirm them to be illusory, are by no means hallucinations having no real object as their correlative, but merely illusions in the narrow sense, and illusions, moreover, in which the ratio of truth to error seems to be a large one.

It would thus appear that philosophy tends, after all, to unsettle what appear to be permanent convictions of the common mind and the presuppositions of science much less than is sometimes imagined. Our intuitions of external realities, our indestructible belief in the uniformity of nature, in the nexus of cause and effect, and so on, are, by the admission of all philosophers, at least partially and _relatively_ true; that is to say, true in relation to certain features of our common experience. At the worst, they can only be called illusory as slightly misrepresenting the exact results of this experience. And even so, the misrepresentation must, by the very nature of the case, be practically insignificant. And so in full view of the subtleties of philosophic speculation, the man of science may still feel justified in regarding his standard of truth, a stable consensus of belief, as above suspicion.

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INDEX.

A.

Abercrombie, Dr. J, 141, note[82], 278.

Abnormal life, relation of, to normal, 1, 120, 121, 124, 182, 277, 284, note[132], 336; effects of amputation, 62; modification of sensibility in, 65; gross sense-illusions of, 111, hallucinations of, 118; sense of personal identity in, 289.

Active, stage in perception, 27; illusion distinguished from passive, 45, 332-334.

Actor. _See_ Theatre.

Adaptation, illusion as want of, 124, 188, 339.

Æsthetic intuition, 213; illusions of, 214.

After-dreams, 144, 183.

After-sensation, after-impression, 55, 115.

Anæsthesia, 65.

Ancestral experience, results of, 281.

Animals, recognition of portraits by, 105; expectation of, 298.

Anthropomorphism, 225, 360.

Anticipation. _See_ Expectation.

Apparitions. _See_ Hallucination.

Aristotle, 130.

Art, illusions of, 77, 104.

Artemidoros, 129.

Association, laws of, in perception, 22; in dreams, 153, 156; link of resemblance in dreams, 159; associative dispositions in dreams, 169; effect of, in insight, 221; inseparable, 359.

Associationist, views of, 349, 352, 355.

Attention, involved in perception 21; absence of, in sense-illusion, 39, 87; relation of, to recognition of objects, 90; expectant, 93; attitude of, in dreaming, 137, 172; to internal mental states, 194; absence of, in errors of insight, 228.

Authority, influence of, in introspection, 210; in belief, 325.

Autobiography, errors connected with, 276, 280.

Automatic activity of centres, in hallucinations, 113; in dreams, 136, 151; automatic intellectual processes, 300, 335, 352.

B.

Baillarger, J., 13, note[1], 113, note[57], 119, notes[64] and [65], 120, note[66].

Bain, Dr. A., 32, note[12], 117, note[60], 190.

Beattie, J., 141, note[82].

Beauty, sentiment of, 206, 213.

Belief, immediate, 14, 15, 294; simple and compound, 296; illusory forms of, 297; simple expectation, 297; expectation, of extra-personal experiences, 307; retrospective, 309; in persistent objects and persons, 312; self-esteem, 315; representation of classes of things, 322; representations of mankind, 322; representation of life and the world as a whole, 322; as predisposition to error, 324; amount of divergence in, 325; tendency towards convergence in, 326.

Beneficial, correct knowledge as, 340; illusion as, 342.

Berkeley, Bishop, 218, 349, note[154].

Binet, A., 53, note[20].

Boismont, Brierre de, 11, note[1].

Börner, J., 146.

Braid, James, 186, 187.

Brewster, Sir D., 42, 73, 81, 116.

Brücke, E., 77, note[38].

Byron, Lord, 116.

C.

Carpenter, Dr. W.B., 32, note[12], 108, 110, note[56], 186, 231, note[111], 265, note[125], 276.

Castle-building, as illusory perception, 3, 99.

Cause, idea of, in science, 344; reality of relation of, 347, 349, 356, 360.

Change, a condition of conscious life, 252, 287, note[133].

Childhood, our recollections of, 263, 269.

Children, curiosity of, 175, 180; estimate of time by, 256; confusion of dream and waking life by, 276; imagination of, 279; self-assertion of, 319; intellectual condition of, 357, note[159].

Clarke, Dr. E.H., 117.

Classification, in recognition of sensation, 21; in recognition, of object, 24; in introspective recognition, 193.

Clifford, Professor W.K., 56, note[24].

Coalescence, of sensations, 43, 52; of dream-images, 162; of internal feelings, 196; of mnemonic images, 265.

Coenæsthesis, 41, 99, 145, 286, 288.

Cognition, immediate or intuitive, 5, 14-16, 294; presentative and representative, 9, 13, 217, 330; nature of, in dreams, 168, 172; nature of, generally, 295, 331; philosophic problems of, 346.

Colour, external reality of, 8, 37; illusory perception of, 37, 88; subjective complementary colours (colour-contrast), 67, 83.

Coloured media, objects seen through, 82.

Common cognition, and truth, 337; genesis and validity of, 353.

Common experience distinguished from individual, 26, 27, 137, 209, 214, 336, 351; illusion as, 47,325, 337.

Common sense, intuitions of, 346, 349, 352, 357.

Complementary colours, 67, 83.

Concave, apparent conversion of, into convex, 84.

Conjuror, tricks of, 56, 106.

Consciousness, veracity of, 192, 205; inspection of phenomena of, 196; of self, 283, 285.

Consensus, the standard of truth, 7, 8, 211, 325, 338, 357.

Conservation of energy, 343.

Construction, rational, in dreams, 170.

Continuum, the perception of the world as, 52, 56, note[24].

Correction of illusion, in sense-illusion, 38, 124, 137; dreams, 182; introspection, 210; insight, 229; memory, 291; historical correction 338; intellectual processes involved in, 351.

Criterion of illusion, 337.

Cudworth, R., 161

D.

Deception of the senses, 19; self-deception, 200; conscious deception of others, 222.

Delboeuf, J., 175, note[97], 235, note[113].

_Delirium tremens_, 118, note[62].

Democritus, 130.

De Quincey, 253, 280.

Descartes, R., 116, 350.

Dickens, Charles, 277.

Direction, illusory sense of, in vision, 66, 71, 73; in hearing, 72, 75.

Disease. _See_ Abnormal life.

Dissolution. _See_ Evolution.

Doubt, starting-point in philosophy, 350.

Dreams, relation of, to illusions of sense, 18, 130; and waking experience, 127; theories of, 128; physiology of, 131; extent of, in sleep, 132; psychological conditions of, 136; excitants of, 139, 143; exaggeration in, 147; symbolism of, 149; as results of automatic activity of centres, 151; as results of association, 153; structure of, 156; incoherent, 156; coherent, 161; action of feeling in, 164; play of associative dispositions in, 168; co-operation of attention and intelligence in, 172; limits of intelligence in, 180; after-dreams, 183, 274; relation of, to hypnotic condition, 185; experience of, in relation to errors of memory, 273.

E.

Eccentricity, law of, 59.

Ego. _See_ Self.

Emotion, and illusion of perception, 103; and hallucination, 115; and bodily sensations, 150; control of dreams by, 164; introspection of, 199; and illusion of introspection, 203; and æsthetic intuition, 213; and illusion of memory, 270; and illusion of belief, 306, 324; and cognition generally, 357, note[159].

Empiricism, philosophic, 348.

_Ennui_, and sense of time, 250.

Environment, sources of sense-illusion in, 47, 48, 70; view of, in mental disease, 290, 326; view of, in normal life, 323; action of, in assimilating belief, 339.

Error, immediate and mediate, 6, 334.

Esquirol, J.E.D., 12, note[2].

Evolution, relation of, to dissolution, 122; of power of introspection, 209; of power of insight, 230; and self-assertion, 320; evolutionist's view of error, 339; doctrine of, as science, 346.

Exaggeration, in interpretation of sensations, 65; in dream-interpretation, 147; in memory, 269.

Expectation, preliminary to perception, 30; and illusory perception, 93, 102, 106; nature of, 295; and memory, 298; of new experience, 301; of remote events, 302; measurement of duration in, 302; action of imagination in, 305; extension of meaning of, 307, 308.

Experience, effect of, in perception, 22, 68, 85, 86, 91; external and internal, 194, 210; revivals of waking, in dreams, 152; effects of present, on retrospection, 267; anticipation of new, 301.

External world. _See_ World.

F.

Fallacy and illusion 6, 335; of testimony, 265.

Familiarity, sense of, in new objects, 272, 281.

Fechner, G.T., 51.

Ferrier, Dr., 32, note[12], 58, note[26].

Fiction, as producing illusion, 278, 279, 311.

Fitness. _See_ Adaptation.

Flattery, _rationale_ of, 200, 222.

Forgetfulness and illusion, 278, 279, 311.

Free-will, doctrine of, 207, 342, 356.

Future. _See_ Expectation.

G.

Galton, F., 117.

Ghosts. _See_ Hallucination.

Goethe, 116, 117, 280 and note[131].

Griesinger, W., 13, note[2], 63, note[31], 66, note[32], 115, 118, note[62], 119, note[64], 120, note[66], 290, note[135], 327, note[146].

Gruithuisen, 143, 144.

Gurney, E., 224, note[109].

H.

Hall, G.S., 186, note[102].

Hallucination, and illusion, 11, 109, 111, 112, 121; and subjective sensation, 63, 109, 121; sensory and motor, 66; nervous conditions of, 112-114; incomplete and complete, 113; as having either central or peripheral origin, 113; causes of, classified, 115; in sane condition, 116; in insanity, 118; visual and auditory, 119; dreams regarded as, 139, 151; hypnagogic, 143; after-dreams and ghosts, 183; of memory, 271; relation of, to errors of belief, 322; intuition of external world regarded as, 355.

Happiness, feeling of, 200.

Harmful, illusion as, 188, 229, 292, 339.

Harmless, illusions as, 124, 292, 341.

Hartley, D., 139, 256, note[124], 279.

Hearing, as mode of perception, 34, 48; localization of impression in, 60; sense of direction in, 72; activity of, in sleep, 140; and muscular sense, 171.

Heidenhain, Dr., 186-188.

Helmholtz, H., 22, 23, note[7], 44, 51, 54 and note[22], 55, note[23], 57, 67, note[33], 78, note[39], 80, 85, note[43], 88, 90, 207, note[105].

Heraclitus, 137.

Heredity, and illusion of memory, 280; action of, in perpetuating intuition, 359.

Hering, E., 67, note[33].

Hodgson, Shadworth H., 347, note[153].

Holland, Sir H., 277.

Hood, Thomas, 146.

Hope, illusory. _See_ Expectation.

Hoppe, Dr. J.I., 51, 58, note[26].

Horwicz, A., 145, note[85].

Hume, D., 355.

Huxley, Professor T., 119, note[1].

Hyperæsthesia, 65.

Hypnotism, 185.

Hypochondria, 65.

Hypothesis, as illusory, 310, 311.

I.

Idealism, 348.

Identity, cases of mistaken, 267.

Identity, personal, confusion of, in dreams, 163; consciousness of, 241, 267, 282, 285; illusory forms of, 283; gross disturbances of, in normal life, 287; in abnormal life, 289; momentary confusions of, 293.

Illusion, definition of, 1; varieties of, 9; extent of, 328; _rationale_ of, 331, 337.

Image (physical). _See_ Reflection.

Image (mental), in perception, 22; seat of, 32; in dreams, 138; mnemonic, 236.

Imagination, play of, in perception, 95, 99; and sense-illusion, 106; nature of, in dreaming, 136, 161; as antecedent of dream, 152, 158; as poetic interpretation of nature, 224; memory corrupted by effect of past, 264, 273, 277; present, creating the semblance of recollection, 267, 271; play of, in expectation, 305; as element of illusion generally, 333.

Immediate. _See_ Cognition.

Individual, and common experience, 26, 27, 137, 209, 214, 336; dream-experience as, 44, 68; internal experience as, 209; memory as, 232; belief and truth, 338.

Inference, and immediate knowledge, 6, 334; in perception, 22, 26, 68; in belief, 295.

Innate, recollection as, 280; principles, 295, 356.

Insane, sense-illusions of, 63, 65, 111; hallucinations of, 118; dreaming and state of, 182; mnemonic illusions of, 278, 289; beliefs of, 327.

Insight, nature of, 217; illusions of, defined, 220; passive illusions of, 220; histrionic illusion, 222; active illusions of, 223; poetic interpretation of nature, 224; value of faculty of, 228.

Interpretation, in correct perception, 22; of impression and experience, 70; and volition, 95; and fixed habits of mind, 101; and temporary attitude of mind, 102; of sensations in dreams, 137, 147; of internal feelings, 203; of others' feelings, 217; of nature by poet, 225; recollection as, 242.

Introspection, nature of, 14, 189; illusory forms of, 190; confusion of inner and outer experiences, 194; inaccurate inspection of feelings, 196; presentation and representation confused, 199; feelings and inferences from these, 203; moral self-scrutiny, 204; philosophic, 205; value of, 208.

Intuition. _See_ Cognition.

Intuitivism, 348.

J.

Jackson, Dr. J. Hughlings, 27, note[9], 33, 123, note[67].

Johnson, Dr., 116.

K.

_Klang_, as compound sensation, 53.

Knowledge. _See_ Cognition.

L.

Language, function of, 195.

Leibnitz, 133.

Lélut, L.F., 120, note[66].

Lessing, G. E., 133, note[73].

Leuret, 290, note[135].

Lewes, G.H., 28, 32, note[12], 52, note[30], 62, note[1], 68, note[35], 89, note[45], 115, note[58], 150.

Life, our estimate of, 323, 326, 327.

Light, sensation and perception of, 59; effects of reflection and refraction, of, 73; representation, of, in painting, 88, 91; action of, in sleep, 140.

Localization, as local discrimination of sensations, 52; as localizing of sensations, 59, 60; illusory, 61, 82; in hallucination, 118, 119; in dreaming, 148; of events in time, in memory, 238, 245; in expectation, 304.

Locke, 133, note[73].

Lotze, H., 60, note[29].

Lover, illusion of, 224, 227, 342.

Luminosity of painting, 88, 91.

Lustre, as compound sensation, 54.

Lyell, Sir Charles, 311.

M.

Magic, arts of, 73.

Magnitude, apparent, in vision, 75, note[37]; perception of, in pictorial art, 88, 91; of time-intervals, 245, 249; recollection of, 268.

Malebranche, 116.

Mankind, our views of, 322.

Matter. _See_ World (material).

Maudsley, Dr. H., 32, note[12].

Maury, A., 140, 143, 153, note[92], 159, 163, note[94], 173.

Mayer, Dr. A., 66, note[32].

Measurement, subjective, of time, 245.

Media, coloured, illusions connected with presence of, 82.

Memory, nature of, 9, 13, 231; veracity of, 232, 290; defined, 234; psychology of, 236; physiology of, 237; localization of events in, 238; and sense of personal identity, 241, 283; illusions of, 241; illusory localization, 245, 256; distortions of, 261; hallucinations of, 271; illusions respecting personal identity, 283; relation of, to belief, 295; compared with expectation, 297; and inference, 335.

Metempsychosis, 294.

Meyer, H., 83, 144.

Mill, J.S., 298, note[138], 309.

Mirrors, as means of delusion, 73.

Misanthropist, 2, 323.

Mitchell, Dr. Weir, 62.

Monomania, 111.

Moral, intuition, 216; self-inspection, 204.

Motor illusions. _See_ Muscular sense.

Movement, apparent, 50, 57, 73, 81, 95, 107; in dreams, 142, 154.

Müller, Johannes, 58, note[27], 100, 117, 143.

_Muscæ volitantes_, 118, note[62].

Muscular sense, in perception, 23; illusions connected with, 50, 57, 62, 66; co-operation, of, in dreams, 142, 154.

Music, subjective interpretation of, 223.

N.

Natural selection, effect of, in eliminating error, 340.

Nature, personification of, 224; uniformity of, 344, 360.

Necessity, idea of, 349, 360.

Nervous system, and conditions of perception, 31; connections of, 32, 169; function of, and force of stimulus, 47, 50; prolonged activity of, 55; specific energy of, 58; variations in state of, 64; fatigue of, 65, 115; disease of, _ibid._; nervous conditions of hallucination, 112, 115; nervous dissolution and evolution, 122; condition of, in sleep, 131; in hypnotic condition, 186; nervous conditions of memory, 237; nervous conditions of illusion in general, 334.

Normal life, relation of, to abnormal, 1, 121, 124, 182, 277, 284, note[132]; hallucinations of, 116.

O.

Object, nature of, 36, 353.

Objective and subjective experience, 26, 27, 137, 214.

Old age, dreams how regarded in, 276.

Oneirocritics, 129.

Opera, illusion connected with, 104.

Optimism, 323, 327, 342.

Organic sensations, discrimination of, 41; interpretation of, 99; in sleep, 145, 148.

Organism, conditions of illusion in, 47, 50; relation of our conception of the universe to sensibilities of, 343.

Orientation, 125, 138.

P.

Pain, recollection of, 264, 270.

Painting, representation of third dimension by, 77; apparent movement of eye in portrait, 81; discrepancies between, and object in magnitude and luminosity, 88; realization of, and mental preparation, 105; realization of, by animals, 105.

Paræsthesia, 68.

Paralysis of ocular muscles, 66.

Passive, and active factor in perception, 27; and active illusion, 45.

Percept, 22; and sense-impression, 59.

Perception, a form of immediate knowledge, 10, 13, 17, 18; external and internal, 14; philosophy of, 14, 20, 22, 36, 346, 348, 353, 355, 359; illusions of, 19, 35; psychology of, 20; and inference, 22, 26, 76; physiological conditions of, 31.

Persistent objects, representation of, 312.

Persistent self. _See_ Personal identity.

Personal equation, in perception, 101; in æsthetic intuition, 214; in memory, 292; in belief, 324.

Personal identity, consciousness of, 241, 282, 285; illusions connected with, 283; disturbances in sense of, 287; sense of, in insanity, 289; momentary confusions of, 293; philosophic problem of, 285, 354, 360.

Personification of nature, 224.

Perspective, linear, 79, 97, 98; aerial, 80; of memory, 245.

Pessimism, 323, 327.

Phenomenalism, 348.

Philosophy, conception of illusion by, 7, 36, 205, 285, 349; of mind, 132, 285, 344, 348; as theory of knowledge, 295, 346; and science, 346, 348; and common sense, 347, 349; problems of, 347.

Phosphenes, 58.

Physical science. _See_ Science.

Plato, 281.

Platonists, 349.

Pleasure, feeling of, 200; recollection of, 264, 270.

Plutarch, 133, note[73].

Poetry, lyrical and dreams, 164; misinterpretation of, 223; personification, 224.

Points, discrimination of, 52.

Poisons, action of, 115.

Pollock, F., 184, note[101].

Pollock, W.H., 184.

Predisposition, action of, in perception, 44, 101, 102; in æsthetic intuition, 215; in insight, 223; in recollection, 268; in belief, 305, 319; belief as, 324.

Prejudice. _See_ Predisposition.

Prenatal experience, recollection of, 281.

Preperception, 27; illusions connected with, 44, 93; voluntary, 95; result of habit of mind, 101; result of temporary conditions, 102; as sub-expectation, 102; as definite expectation, 106.

Presentation and representation, 9, 10, 13, 14, 192, 234, 329, 330.

Projection, outward, of sensations, 63; of mental image, 111, 112; of solid form on flat, 79, 81, 96.

Prophetic, dreams as, 129, 147, note[88]; enthusiast, 307.

Psychology, popular and scientific, 9, 10; distinguished from philosophy, 14, 36, 345, 352; introspective method of, 208; as a kind of philosophy, 305.

Public events, localization, of, by memory, 258.

R.

Radestock, P., 130, note[71], 132, note[72], 134, note[75], 140, 141, 149, note[90], 162, 182, 275.

Rationalism, philosophic, 348.

Realism, 348.

Reality, nature of, 36, 346.

Recognition, and perception, 24, 25; illusions of, 87; and memory, 234.

Reflection (of light), illusions connected with, 73, 83.

Refraction and optical illusion, 73.

Relative, sensation as, 64; attention to magnitude and brightness as, 91; estimate of duration as, 249.

Relief, illusory perception of, 75, 96.

Representation and presentation, 9, 10, 13, 14, 192.

Retrospection. _See_ Memory.

Ribot, T., 238, note[114], 290, note[135].

Richter, J.P., 143.

Robertson, Professor G.C., 35, note[14].

Romanes, G.J., 105, note[2], 250, note[122].

Rousseau, 280.

S.

Savage, dream theory of, 128; idea of nature of, 225.

Scherner, C.A., 140, 149.

Schopenhauer, A., 145, 342.

Schroeder, H., 85.

Science, philosophy and, 8, 36, 285, 344; conception of the material world in physical, 36, 343, 346, 347; and common cognition, 338, 357.

Scott, Sir W., 116, 125.

Secondary qualities, 36, 344.

Selection, process of, in perception, 95; in dreams, 174; in memory, 257, 263.

Self, confusion of, in dreams, 163; introspective knowledge of, 192; self-deception, 200; identity of, 241, 282, 285; confusion of present and past, 267, 284; disturbances in recognition of, 287, 289; momentary confusions of, 295; confusion of present and future, 305.

Self-esteem, illusion of, 315; origin of, 319; utility of, 342.

Self-preservation, 320.

Sensation, element in perception, 20; discrimination and classification of, 21; interpretation of, 22; inattention to, 39, 87; modified by central reaction, 39, 87, 89, 91; confusion of novel, 40; indistinct, 41; misinterpretation of, 44; relation of, to stimulus, 46, 50; limits to discrimination of, 52; after-impression, 55; subjective, 59, 62, 107, 143; localization of, 59.

Sensibility, limits of, 50; variations of, 64.

Sensualism, philosophic, 348.

Shadow, cast, 77.

Shakespeare, 3.

Sight, mode of perception, 19, 33, 34, 48, 49; local discrimination in, 52; single vision, 54; localization of impression in, 60; in sleep, 139; images of, in sleep, 150, 154.

Single, vision, 54; touch, 72.

Sleep, mystery of, 127; physiology of, 131.

Sleight of hand. _See_ Conjuror.

Smell, as mode of perception, 34, note[14]; localization of impression in, 60; subjective sensations of, 108; in sleep, 141; and taste, 171.

Solidity, illusory perception of, 75, 96.

Space, representation of, 207.

Specific energy of nerves, 58.

Spectra, ocular, etc. _See_ Subjective sensation.

Spencer, Herbert, 32, note[12], 128, note[69], 323, 340.

Spinoza, 143, 184.

Spiritualist _séances_, 103, 107, 123, 265.

Stereoscope, 75.

Stewart, Dugald, 172, 306.

Stimulus, qualitative relation of, to sensations, 46, 58, 67; quantitative relation of, to sensation, 50, 64; after-effect of, 55; prolonged action of, 56; subjective or internal, 62; exceptional relation of, to organ, 70; action of, in sleep, 135, 139, 143; in hypnotic condition, 186.

Strümpell, L., 144, 147, note[89].

Subjective, experience, 26, 27, 137, 214; movement, 51, 57; sensation, 59, 62, 107, 113, 121, 143.

Suggestion, by external circumstances, 30, 44, 89, 91, 267; verbal, 30, 106, 188, 215, 268, 301, 310.

Symbol, dream as, 129, 149.

Sympathy, basis of knowledge, 223; and illusion of insight, 223; and illusion of memory, 277; and momentary illusion, 293.

T.

Taine, H., 60, note[29], 108, note[54], 117, note[59], 137, 298, note[137], 356, note[158].

Taste, æsthetic. _See_ Æsthetic intuition.

Taste, localization of impression in, 60; subjective sensations of, 63; variations in sensibility, 68; activity of, in sleep, 141; and smell, 171.

Temperament, a factor in sense-illusion, 101; in dreams, 137; in illusory belief, 325; in illusion generally, 334, note[149].

Temperature, sense of, 65.

Tennyson, A., 226.

Testa, A.J., 131.

Testimony, of consciousness, 205; fallacies of, 265; to identity, 267.

Thaumatrope, 56.

Theatre, illusion of the, 104, 222; self-deception of the actor, 200.

Thompson, Professor S.P., 51, note[17].

Thought, in relation to belief, 326.

Time, retrospective idea of, 239, 246, 250; constant error in estimate of, 245; subjective estimate of, 249; contemporaneous estimate of, 250; sense of, in insanity, 290; prospective estimate of, 303.

Touch, as form of perception, 33, 34, 49; local discrimination in, 52; subjective sensations of, 62; variations in sensibility of, 65; in sleep, 141.

Transformation, in perception, 94; of images in dreams, 163; in memory, 262, 267; in expectation, 305.

Trick. _See_ Conjuror.

Tuke, Dr., 110.

Tylor, E.B., 128, note[69].

U.

Unconscious, inference, 22, 68, 269, 335, note[150]; mental activity, 133, 235; impressions, 41, 152.

Useful. _See_ Beneficial.

V.

Vanity. _See_ Self-esteem.

Venn, J., 299, note[139].

Ventriloquism, 82.

Verification, of sense-impression, 38, 351; of self-inspection, 210; of memory, 291.

Verisimilitude, in art, 80, 88; in theatrical representation, 104; in dreams, 168.

Vierordt, 245.

Vision. _See_ Sight.

Visions, 1, 110; dreams regarded as, 128, 131.

Vital sense. _See_ Coenæsthesis.

Voice, internal, 119, 194; activity of, in dreams, 155.

Volition, and perception, 95; absence of, during sleep, 137,172; co-operation of, in correction, of illusion, 352.

Volkelt, J., 172.

W.

Weber, E.H., 43.

Weinhold, Professor, 186.

Wetness, perception of, 53.

Wheatstone, Sir C, 75.

Wheel of life, 56.

Will. _See_ Volition.

Wordsworth, W., 281.

World, our estimate of, 323, 326, 327; scientific conception of material, 8, 36, 343, 344; reality of external, 344-346, 349, 353, 355, 360.

Wundt, Professor, W. 13, note[2], 31, note[11], 32, note[12], 58, note[27], 67, note[34], 75, 93, note[47], 118, note[63], 136, note[77], 139, 143, 177, 246, 247, note[119], 251, 252, 254.

THE END

FOOTNOTES:

[1] A history of the distinction is given by Brierre de Boismont, in his work _On Illusions_ (translated by R. T. Hulme, 1859). He says that Arnold (1806) first defined hallucination, and distinguished it from illusion. Esquirol, in his work, _Des Maladies Mentales_ (1838), may be said to have fixed the distinction. (See Hunt's translation, 1845, p. 111.)

[2] This fact has been fully recognized by writers on the pathology of the subject; for example, Griesinger, _Mental Pathology and Therapeutics_ (London, 1867), p. 84; Baillarger, article, "Des Hallucinations," in the _Mémoires de l'Académie Royale de Médecine_, tom. xii. p. 273, etc; Wundt, _Physiologische Psychologie_, p. 653.

[3] I here touch on the distinction between the psychological and the philosophical view of perception, to be brought out more fully by-and-by.

[4] It might even be urged that the order here adopted is scientifically the best, since sense-perception is the earliest form of knowledge, introspected facts being known only in relation to perceived facts. But if the mind's knowledge of its own states is thus later in time, it is earlier in the logical order, that is to say, it is the most strictly presentative form of knowledge.

[5] Here and elsewhere I use the word "impression" for the whole complex of sensation which is present at the moment. It may, perhaps, not be unnecessary to add that, in employing this term, I am making no assumption about the independent existence of external objects.

[6] Psychological usage has now pretty well substituted the term "image" for "idea," in order to indicate an individual (as distinguished from a general) representation of a sensation or percept. It might, perhaps, be desirable to go further in this process of differentiating language, and to distinguish between a sensational image, _e.g._ the representation of a colour, and a perceptional image, as the representation of a coloured object. It may be well to add that, in speaking of a fusion of an image and a sensation, I do not mean that the former exists apart for a single instant. The term "fusion" is used figuratively to describe the union of the two sides or aspects of a complete percept.

[7] This impulse to fill in visual elements not actually present is strikingly illustrated in people's difficulty in recognizing the gap in the field of vision answering to the insensitive "blind" spot on the retina. (See Helmholtz, _Physiologische Optik_, p. 573, _et seq._)

[8] This relation will be more fully discussed under the head of "Memory."

[9] I adopt this distinction from Dr. J. Hughlings Jackson. See his articles, "On Affections of Speech from Diseases of the Brain," in _Brain_, Nos. iii. and vii. The second stage might conveniently be named apperception, but for the special philosophical associations of the term: _Problems of Life and Mind_, third series, p. 107. This writer employs the word "preperception" to denote this effect of previous perception.

[10] Such verbal suggestion, moreover, acting through a sense-impression, has something of that vividness of effect which belongs to all excitation of mental images by external stimuli.

[11] See Wundt, _Physiologische Psychologie_, p. 723.

[12] For a confirmation of the view adopted in the text, see Professor Bain, _The Senses and the Intellect_, Part II. ch. i. sec. 8; Herbert Spencer, _Principles of Psychology_, vol. i. p. 234, _et passim_; Dr. Ferrier, _The Functions of the Brain_, p. 258, _et seq._; Professor Wundt, _op. cit._, pp. 644, 645; G. H. Lowes, _Problems of Life and Mind_, vol. v. p. 445, _et seq._ For an opposite view, see Dr. Carpenter, _Mental Physiology_, fourth edit., p. 220, etc.; Dr. Maudsley, _The Physiology of Mind_, ch. v. p. 259, etc.

[13] See note, p. 22.

[14] Touch gives much by way of interpretation only when an individual object, for example a man's hat, is recognized by aid of this sense alone, in which case the perception distinctly involves the reproduction of a complete visual percept. I may add that the organ of smell comes next to that of hearing, with respect both to the range and definiteness of its simultaneous sensations, and to the amount of information furnished by these. A rough sense of distance as well as of direction is clearly obtainable by means of this organ. There seems to me no reason why an animal endowed with fine olfactory sensibility, and capable of an analytic separation of sense elements, should not gain a rough perception of an external order much more complete than our auditory perception, which is necessarily so fragmentary. This supposition appears, indeed, to be the necessary complement to the idea first broached, so far as I am aware, by Professor Croom Robertson, that to such animals, visual perception consists in a reference to a system of muscular feelings defined and bounded by strong olfactory sensations, rather than by tactual sensations as in our case.

[15] It may be said, perhaps, that the exceptional direction of attention, by giving an unusual intensity to the impression, causes us to exaggerate it just as in the case of a novel sensation. An effort of attention directed to any of our vague bodily sensations easily leads us to magnify its cause. A similar confusion may arise even in direct vision, when the objects are looked at in a dim light, through a want of proper accommodation. (See Sir D. Brewster, _op. cit._, letter i)

[16] They might also be distinguished as objective and subjective illusions, or as illusions _a posteriori_ and illusions _a priori_.

[17] _Die Schein-Bewegungen_, von Professor Dr. J.I. Hoppe (1879); _cf._ an ingenious article on "Optical Illusions of Motion," by Professor Silvanus P. Thompson, in _Brain_, October, 1880. These illusions frequently involve the co-operation of some preconception or expectation. For example, the apparent movement of a train when we are watching it and expecting it to move, involves both an element of sense-impression and of imagination. It is possible that the illusion of table-turning rests on the same basis, the table-turner being unaware of the fact of exerting a certain amount of muscular force, and vividly expecting a movement of the object.

[18] _Physiologische Optik_, p. 316.

[19] It is plain that this supposed error could only be brought under our definition of illusion by extending the latter, so as to include sense-perceptions which are contradicted by reason employing idealized elements of sense-impression, which, as Lewes has shown (_Problems of Life and Mind_, i. p. 260), make up the "extra-sensible world" of science.

[20] An ingenious writer, M. Binet, has tried to prove that the fusion of homogeneous sensations, having little difference of local colour, is an illustration of this principle. (See the _Revue Philosophique_, September, 1880.)

[21] Even the fusion of elementary sensations of colour, on the hypothesis of Young and Helmholtz, in a seemingly simple sensation may be explained to some extent by these circumstances, more especially the identity of local interpretation.

[22] The perception of lustre as a single quality seems to illustrate a like error. There is good reason to suppose that this impression arises through, a difference of brightness in the two retinal images due to the regularly reflected light. And so when this inequality of retinal impression is imitated, as it may easily be by combining a black and a white surface in a stereoscope, we imagine that we are looking at one lustrous surface. (See Helmholtz, _Physiologische Optik_, p. 782, etc., and _Populäre wissenschaftliche Vorträge_, 2tes Heft, p. 80.)

[23] The conditions of the production of these double images have been accurately determined by Helmholtz, who shows that the coalescence of impressions takes place whenever the object is so situated in the field of vision as to make it practically necessary that it should be recognized as one.

[24] These illusions are, of course, due in part to inattention, since close critical scrutiny is often sufficient to dispel them. They are also largely promoted by a preconception that the event is going to happen in a particular way. But of this more further on. I may add that the late Professor Clifford has argued ingeniously against the idea of the world being a continuum, by extending this idea of the wheel of life. (See _Lectures and Essays_, i. p. 112, _et seq._)

[25] It is supposed that in the case of every sense-organ there is always some minimum forces of stimulus at work, the effect of which on our consciousness is _nil_.

[26] See Helmholtz, _Physiologische Optik_, p. 603. Helmholtz's explanation is criticised by Dr. Hoppe, in the work already referred to (sec. vii), though I cannot see that his own theory of these movements is essentially different. The apparent movement of objects in vertigo, or giddiness, is probably due to the loss, through a physical cause, of the impressions made by the pressure of the fluid contents of the ear on the auditory fibres, by which the sense of equilibrium and of rotation is usually received. (See Ferrier, _Functions of the Brain_, pp. 60, 61.)

[27] I do not need here to go into the question whether, as Johannes Müller assumed, this is an original attribute of nerve-structure, or whether, as Wundt suggests, it is due simply to the fact that certain kinds of nervous fibre have, in the course of evolution, been slowly adapted to one kind of stimulus.

[28] I here refer to what is commonly supposed to be the vague innate difference of sensation according to the local origin, before this is rendered precise, and added to by experience and association.

[29] The illusory character of this simple mode of perception is seen best, perhaps, in the curious habit into which we fall of referring a sensation of contact or discomfort to the edge of the teeth, the hair, and the other insentient structures, and even to anything customarily attached to the sentient surface, as dress, a pen, graving tool, etc. On these curious illusions, see Lotze, _Mikrokosmus_, third edit., vol. ii. p. 202, etc.; Taine, _De l'Intelligence_, tom. ii. p. 83, _et seq._

[30] Quoted by G.H. Lewes, _Problems of Life and Mind_, third series, p. 335. These illusions are supposed to involve an excitation of the nerve-fibres (whether sensory or motor) which run to the muscles and yield the so-called muscular sensations.

[31] It is brought out by Griesinger (_loc. cit._) and the other writers on the pathology of illusion already quoted, that in the case of subjective sensations of touch, taste, and smell, no sharp line can be drawn between illusion and hallucination.

[32] For a fuller account of these pathological disturbances of sensibility, see Griesinger; also Dr. A. Mayer, _Die Sinnestäuschungen_.

[33] Helmholtz, _op. cit._, p. 600, _et seq._ These facts seem to point to the conclusion that at least some of the feelings by which we know that we are expending muscular energy are connected with the initial stage of the outgoing nervous process in the motor centres. In other pathological conditions the sense of weight by the muscles of the arms is similarly confused.

[34] Wundt (_Physiologische Psychologie_, p. 653) would exclude from illusions all those errors of sense-perception which have their foundation in the normal structure and function of the organs of sense. Thus, he would exclude the effects of colour-contrast, _e.g._ the apparent modification of two colours in, juxtaposition towards their common boundary, which probably arises (according to E. Hering) from some mutual influence of the temporary state of activity of adjacent retinal elements. To me, however, these appear to be illusions, since they may be brought under the head of wrong _interpretations_ of sense-impressions. When we see a grey patch as rose-red, as though it were so independently of the action of the complementary light previously or simultaneously, that is to say, as though it would appear rose-red to an eye independently of this action, we surely misinterpret.

[35] Quoted by G.H. Lewes, _loc. cit._, p. 257.

[36] The subject of the perception of movement is too intricate to be dealt with fully here. I have only touched on it so far as necessary to illustrate our general principle. For a fuller treatment of the subject, see the work of Dr. Hoppe, already referred to.

[37] The perception of magnitude is closely connected with that of distance, and is similarly apt to take an illusory form. I need only refer to the well-known simple optical contrivances for increasing the apparent magnitude of objects. I ought, perhaps, to add that I do not profess to give a complete account of optical illusions here, but only to select a few prominent varieties, with a view to illustrate general principles of illusion. For a fuller account of the various mechanical arrangements for producing optical illusion, I must refer the reader to the writings of Sir D. Brewster and Helmholtz.

[38] Painters are well aware that the colours at the red end of the spectrum are apt to appear as advancing, while those of the violet end are known as retiring. The appearance of relief given by a gilded pattern on a dark blue as ground, is in part referable to the principle just referred to. In addition, it appears to involve a difference in the action of the muscles of accommodation in the successive adaptations of the eye to the most refrangible and the least refrangible rays. (See Brücke, _Die Physiologie der Farben_, sec. 17.)

[39] Helmholtz tells us (_Populäre wissenschaftliche Vorträge_, 3tes Heft, p. 64) that even in a stereoscopic arrangement the presence of a wrong cast shadow sufficed to disturb the illusion.

[40] Among the means of giving a vivid sense of depth to a picture, emphasized by Helmholtz, is diminishing magnitude. It is obvious that the perceptions of real magnitude and distance are mutually involved. When, for example, a picture represents a receding series of objects, as animals, trees, or buildings, the sense of the third dimension, is rendered much more clear.

[41] A striking example of this was given in a painting, by Andsell, of a sportsman in the act of shooting, exhibited in the Royal Academy in 1879.

[42] This is at least true of all near objects.

[43] Helmholtz remarks _(op. cit._, p. 628) that the difficulty of seeing the convex cast as concave is probably due to the presence of the cast shadow. This has, no doubt, some effect: yet the consideration urged in the text appears to me to be the most important one.

[44] _Populäre wissenschaftliche Vorträge_, 3tes Heft, pp. 71, 72.

[45] See, on this point, some excellent remarks by G.H. Lewes, _Problems of Life and Mind_, third series, vol. ii. p. 275.

[46] To some extent this applies to the changes of apparent magnitude due to altered position. Thus, we do not attend to the reduction of the height of a small object which we are wont to handle, when it is placed far below the level of the eye. And hence the error people make in judging of the point in the wall or skirting which a hat will reach when placed on the ground.

[47] I refer to the experiments made by Exner, Wundt, and others, in determining the time elapsing between the giving of a signal to a person and the execution of a movement in response. "It is found," says Wundt, "by these experiments that the exact moment at which a sense-impression is perceived depends on the amount of preparatory self-accommodation of attention." (See Wundt, _Physiologische Psychologie_, ch. xix., especially p. 735. _et seq._)

[48] Quoted by Helmholtz, _op. cit._, p. 626.

[49] When the drawing, by its adherence to the laws of perspective, does not powerfully determine the eye to see it in one way rather than in the other (as in Figs. 5 to 7), the disposition to see the one form rather than the other points to differences in the frequency of the original forms in our daily experience. At the same time, it is to be observed that, after looking at the drawing for a time under each aspect, the suggestion now of the one and now of the other forces itself on the mind in a curious and unaccountable way.

[50] _Ueber die phantastischen Gesichsterscheinungen_, p. 45.

[51] Another side of histrionic illusion, the reading of the imitated feelings into the actors' minds, will be dealt with in a later chapter.

[52] In a finished painting of any size this preparation is hardly necessary. In these cases, in spite of the great deviations from truth in pictorial representation already touched on, the amount of essential agreement is so large and so powerful in its effect that even an intelligent animal will experience an illusion. Mr. Romanes sends me an interesting account of a dog, that had never been accustomed to pictures, having been put into a state of great excitement by the introduction of a portrait into a room, on a level with his eye. It is not at all improbable that the lower animals, even when sane, are frequently the subjects of slight illusion. That animals dream is a fact which is observed as long ago as the age of Lucretius.

[53] This kind of illusion is probably facilitated by the fact that the eye is often performing slight movements without any clear consciousness of them. See what was said about the limits of sensibility, p. 50.

[54] _Mental Physiology_, fourth edit., p. 158.

[55] In persons of very lively imagination the mere representation of an object or event may suffice to bring about such a semblance of sensation. Thus, M. Taine (_op. cit._, vol. i. p. 94) vouches for the assertion that "one of the most exact and lucid of modern novelists," when working out in his imagination the poisoning of one of his fictitious characters, had so vivid a gustatory sensation of arsenic that he was attacked by a violent fit of indigestion.

[56] Mentioned by Dr. Carpenter (_Mental Physiology_, p. 207), where other curious examples are to be found.

[57] See _Annales Médico-Psychologiques_, tom. vi. p. 168, etc.; tom. vii. p. 1. etc.

[58] I have already touched on the resonance of a sense-impression when the stimulus has ceased to act (see p. 55). The remarks in the text hold good of all such after-impressions, in so far as they take the form of fully developed percepts. A good example is the recurrence of the images of microscopic preparations, to which the anatomist is liable. (See Lewes, _Problems of Life and Mind_, third series, vol. ii. p. 299.) Since a complete hallucination is supposed to involve the peripheral regions of the nerve, the mere fact of shutting the eye would not, it is clear, serve as a test of the origin of the illusion.

[59] That subjective sensation may become the starting-point in complete hallucination is shown in a curious instance given by Lazarus, and quoted by Taine, _op. cit._, vol. i. p. 122, _et seq._ The German psychologist relates that, on one occasion in Switzerland, after gazing for some time on a chain of snow-peaks, he saw an apparition of an absent friend, looking like a corpse. He goes on to explain that this phantom was the product of an image of recollection which somehow managed to combine itself with the (positive) after-image left by the impression of the snow-surface.

[60] For an account of Mr. Galton's researches, see _Mind_, No. xix. Compare, however, Professor Bain's judicious observations on these results in the next number of _Mind_. The liability of children to take images for percepts, is illustrated by the experiences related in a curious little work, _Visions_, by E.H. Clarke, M.D. (Boston, U.S., 1878), pp. 17, 46, and 212.

[61] A common way of describing the relation of the hallucinatory to real objects, is to say that the former appear partly to cover and hide the latter.

[62] Griesinger remarks that the forms of the hallucinations of the insane rarely depend on sense-disturbances alone. Though these are often the starting-point, it is the whole mental complexion of the time which gives the direction to the imagination. The common experience of seeing rats and mice running about during a fit of _delirium tremens_ very well illustrates the co-operation of peripheral impressions not usually attended to, and possibly magnified by the morbid state of sensibility of the time (in this case flying spots, _muscæ volitantes_), with emotional conditions. (See Griesinger, _loc. cit._, p. 96.)

[63] Wundt (_Physiologische Psychologie_, p. 652) tells us of an insane woodman who saw logs of wood on all hands in front of the real objects.

[64] It is stated by Baillarger (Mémoires de l'Académie Royale de Médicine, tom. xii. p. 273, etc.) that while visual hallucinations are more frequent than auditory in healthy life, the reverse relation holds in disease. At the same time, Griesinger remarks (_loc. cit._, p. 98) that visual hallucinations are rather more common than auditory in disease also. This is what we should expect from the number of subjective sensations connected with the peripheral organ of vision. The greater relative frequency of auditory hallucinations in disease, if made out, would seem to depend on the close connection between articulate sounds and the higher centres of intelligence, which centres are naturally the first to be thrown out of working order. It is possible, moreover, that auditory hallucinations are quite as common as visual in states of comparative health, though more easily overlooked. Professor Huxley relates that he is liable to auditory though not to visual hallucinations. (See _Elementary Lessons in Physiology_, p. 267.)

[65] See Baillarger, _Mémoires de l'Académie Royale de Médicine_, tom. xii. p. 273, _et seq._

[66] See Baillarger, _Annales Médico-Psychologiques_, tom. vi. p. 168 _et seq._; also tom. xii. p. 273, _et seq._ Compare Griesinger, _op. cit._ In a curious work entitled _Du Démon de Socrate_ (Paris, 1856), M. Lélut seeks to prove that the philosopher's admonitory voice was an incipient auditory hallucination symptomic of a nascent stage of mental alienation.

[67] This is well brought out by Dr. J. Hughlings Jackson, in the papers in _Brain_, already referred to.

[68] _Friend_, vol. i. p. 248. The story is referred to by Sir W. Scott in his _Demonology and Witchcraft_.

[69] See E.B. Tylor, _Primitive Culture_, ch. xi.; _cf._ Herbert Spencer, _Principles of Sociology_, ch. x.

[70] For a fuller account of the different modes of dream-interpretation, see my article "Dream," in the ninth edition of the _Encyclopædia Britannica_.

[71] For a fuller account of the reaction of dreams on waking consciousness, see Paul Radestock, _Schlaf und Traum_. The subject is touched on later, under the Illusions of Memory.

[72] For an account of the latest physiological hypotheses as to the proximate cause of sleep, see Radestock, _op. cit._, appendix.

[73] Plutarch, Locke, and others give instances of people who never dreamt. Lessing asserted of himself that he never knew what it was to dream.

[74] The error touched on here will be fully dealt with under Illusions of Memory.

[75] For a very full, fair, and thoughtful discussion of this whole question, see Radestock, _op. cit._, ch. iv.

[76] This may be technically expressed by saying that the liminal intensity (Schwelle) is raised during sleep.

[77] See Wundt, _Physiologische Psychologie_, pp. 188-191.

[78] There is, indeed, sometimes an undertone of critical reflection, which is sufficient to produce a feeling of uncertainty and bewilderment, and in very rare cases to amount to a vague consciousness that the mental experience is a dream.

[79] _Observations on Man_, Part I. ch. iii, sec. 5.

[80] Quoted by Radestock, _op. cit._, p. 110.

[81] _Le Sommeil et les Rêves_, p. 132, _et seq._

[82] _Das Leben des Traumes_, p. 369. Other instances are related by Beattie and Abercrombie.

[83] _Le Sommeil et les Rêves_, p. 42, _et seq._

[84] _Beiträge sur Physiognosie und Heautognosie_, p. 256. For other cases see H. Meyer, _Physiologie der Nervenfaser_, p. 309; and Strümpell, _Die Natur und Entstehung der Träume_, p. 125.

[85] A very clear and full account of these organic sensations, or common sensations, has recently appeared from the pen of A. Horwicz in the _Vierteljahrsschrift für wissenschaftliche Philosophie_, iv. Jahrgang 3tes Heft.

[86] Schopenhauer uses this hypothesis in order to account for the apparent reality of dream-illusions. He thinks these internal sensations may be transformed by the "intuitive function" of the brain (by means of the "forms" of space, time, etc.) into quasi-realities, just as well as the subjective sensations of light, sound, etc., which arise in the organs of sense in the absence of external stimuli. (See _Versuch über das Geisterschen: Werke_, vol. v. p. 244, _et seq._)

[87] _Das Alpdrücken_, pp. 8, 9, 27.

[88] It is this fact which justifies writers in assigning a prognostic character to dreams.

[89] A part of the apparent exaggeration in our dream-experiences may be retrospective, and due to the effect of the impression of wonder which they leave behind them. (See Strümpell, _Die Natur und Entstehung der Träume_.)

[90] _Cf._ Radestock, _op. cit._, pp. 131, 132.

[91] I was on one occasion able to observe this process going on in the transition from waking to sleeping. I partly fell asleep when suffering from toothache. Instantly the successive throbs of pain transformed themselves into a sequence of visible movements, which I can only vaguely describe as the forward strides of some menacing adversary.

[92] Even the "unconscious impressions" of waking hours, that is to say, those impressions which are so fugitive as to leave no psychical trace behind, may thus rise into the clear light of consciousness during sleep. Maury relates a curious dream of his own, in which there appeared a figure that seemed quite strange to him, though he afterwards found that he must have been in the habit of meeting the original in a street through which he was accustomed to walk (_loc. cit._, p. 124).

[93] See p. 53.

[94] See Maury, _loc. cit._, p. 146.

[95] See what was said respecting the influence of a dominant emotional agitation on the interpretation of actual sense-impressions.

[96] It is proved experimentally that the ear has a much closer organic connection with the vocal organ than the eye has. Donders found that the period required for responding vocally to a sound-signal is less than that required for responding in the same way to a light-signal.

[97] On the nature of this impulse, as illustrated in waking and in sleep, see the article by Delboeuf, "Le Sommeil et les Rêves," in the _Revue Philosophique_, June, 1880, p. 636.

[98] _Physiologische Psychologie_, p. 660.

[99] I may, perhaps, observe, after giving two dreams which have to do with mathematical operations, that, though I was very fond of them in my college days, I have long ceased to occupy myself with these processes. I would add, by way of redeeming my dream-intelligence from a deserved charge of silliness, that I once performed a respectable intellectual feat when asleep. I put together the riddle, "What might a wooden ship say when her side was stove in? Tremendous!" (Tree-mend-us). I was aware of having tried to improve on the form of this pun. I am happy to say I am not given to punning during waking life, though I had a fit of it once. It strikes me that punning, consisting as it does essentially of overlooking sense and attending to sound, is just such a debased kind of intellectual activity as one might look for in sleep.

[100] See Radestock, _op. cit._, ch. ix.; _Vergleichung des Traumes mit dem Wahnsinn_.

[101] For Spinoza's experience, given in his own words, see Mr. F. Pollock's _Spinoza_, p. 57; _cf._ what Wundt says on his experience, _Physiologische Psychologie_, p. 648, footnote 2.

[102] See an interesting account of "Recent Researches on Hypnotism," by G. Stanley Hall, in _Mind_, January, 1881.

[103] I need hardly observe that physiology shows that there is no separation of different elementary colour-sensations which are locally identical.

[104] This kind of error is, of course, common to all kinds of cognition, in so far as they involve comparison. Thus, the presence of the excitement of the emotion of wonder at the sight of an unusually large object, say a mountain, disposes the mind to look on it as the largest of its class. Such illusions come midway between presentative and representative illusions. They might, perhaps, be specially marked off as illusions of "judgment."

[105] So far as any mental state, though originating in a fusion of elements, is now unanalyzable by the best effort of attention, we must of course regard it in its present form as simple. This distinction between what is simple or complex in its present nature, and what is originally so, is sometimes overlooked by psychologists. Whether the feelings and ideas here referred to are now simple or complex, cannot, I think, yet be very certainly determined. To take the idea of space, I find that after practice I recognize the ingredient of muscular feeling much better than I did at first. And this exactly answers to Helmholtz's contention that elementary sensations as partial tones can be detected after practice. Such separate recognition may be said to depend on correct representation. On the other hand, it must be allowed that there is room for the intuitionist to say that the associationist is here reading something into the idea which does not belong to it. It is to be added that the illusion which the associationist commonly seeks to fasten on his opponent is that of confusing final with original simplicity. Thus, he says that, though the idea of space may now to all intents and purposes be simple, it was really built up out of many distinct elements. More will be said on the relation of questions of nature and genesis further on.

[106] I may as well be frank and say that I myself, assuming free-will to be an illusion, have tried to trace the various threads of influence which have contributed to its remarkable vitality. (See _Sensation and Intuition_, ch. v., "The Genesis of the Free-Will Doctrine.")

[107] I purposely leave aside here the philosophical question, whether the knowledge of others' feelings is intuitive in the sense of being altogether independent of experience, and the manifestation of a fundamental belief. The inherited power referred to in the text might, of course, be viewed as a transmitted result of ancestral experience.

[108] I here assume, along with G.H. Lewes and other competent dramatic critics, that the actor does not and dares not feel what he expresses, at least not in the perfectly spontaneous way, and in the same measure in which he appears to feel it.

[109] The illusory nature of much of this emotional interpretation of music has been ably exposed by Mr. Gurney. (See _The Power of Sound_, p. 345, _et seq._)

[110] The reader will note that this impulse is complementary to the other impulse to view all mental states as analogous to impressions produced by external things, on which I touched in the last chapter.

[111] Errors of memory have sometimes been called "fallacies," as, for example, by Dr. Carpenter (_Human Physiology_, ch. x.). While preferring the term "illusion," I would not forget to acknowledge my indebtedness to Dr. Carpenter, who first set me seriously to consider the subject of mnemonic error.

[112] From this it would appear to follow that, so far as a percept is representative, recollection must be re-representative.

[113] The relation of memory to recognition is very well discussed by M. Delboeuf, in connection with a definition of memory given by Descartes. (See the article "Le Sommeil et les Rêves," in the _Revue Philosophique_, April, 1880, p. 428, _et seq._)

[114] A very interesting account of the most recent physiological theory of memory is to be found in a series of articles, bearing the title, "La Mémoire comme fait biologique," published in the _Revue Philosophique_, from the pen of the editor, M. Th. Ribot. (See especially the _Revue_ of May, 1880, pp. 516, _et seq._) M. Ribot speaks of the modification of particular nerve-elements as "the static base" of memory, and of the formation of nerve-connections by means of which the modified element may be re-excited to activity as "the dynamic base of memory" (p. 535).

[115] What constitutes the difference between such a progressive and a retrogressive movement is a point that will be considered by-and-by.

[116] It is not easy to say how far exceptional conditions may serve to reinstate the seemingly forgotten past. Yet the experiences of dreamers and of those who have been recalled to consciousness after partial drowning, whatever they may prove with respect to the revivability of remote experiences, do not lead us to imagine that the range of our definitely localizing memory is a wide one.

[117] _Der Zeitsinn nach Versuchen_, p. 36, _et seq._

[118] _Physiologische Psychologie_, p. 782.

[119] Wundt refers these errors to variations in the state of preadjustment of the attention to impressions and representations, according as they succeed one another slowly or rapidly. There is little doubt that the effects of the state of tension of the apparatus of attention, are involved here, though I am disposed to think that Wundt makes too much of this circumstance. (See _Physiologische Psychologie_, pp. 782, 783. I have given a fuller account of Wundt's theory in _Mind_, No. i.)

[120] Strictly speaking, it would occupy more time, since the effort of recalling each successive link in the chain would involve a greater interval between any two images than that between the corresponding experiences.

[121] I need hardly say that there is no sharp distinction between these two modes of subjective appreciation. Our estimate of an interval as it passes is really made up of a number of renewed anticipations and recollections of the successive experiences. Yet we can say broadly that this is a prospective estimate, while that which is formed when the period has quite expired must be altogether retrospective.

[122] See an interesting paper on "Consciousness of Time," by Mr. G. J. Romanes, in _Mind_ (July, 1878).

[123] It is well known that there is, from the first, a gradual falling off in the strength of a sensation of light when a moderately bright object is looked at.

[124] _Cf._ Hartley, _Observations on Man_, Part I. ch. iii. sec. 4 (fifth edit., p. 391).

[125] See Dr. Carpenter's _Mental Physiology_, fourth edit, p. 456.

[126] This is, perhaps, what is meant by saying that people recall their past enjoyments more readily than their sufferings. Yet much seems to turn on temperament and emotional peculiarities. (For a fuller discussion of the point, see my _Pessimism_, p. 344.)

[127] The only exception to this that I can think of is to be found in the power which I, at least, possess, after looking at a new object, of representing it as a familiar one. Yet this may be explained by saying that in the case of every object which is clearly apprehended there must be vague revivals of _similar_ objects perceived before. Oases in which recent experiences tend, owing to their peculiar nature, very rapidly to assume the appearance of old events, will be considered presently.

[128] _Mental Physiology_, p. 456.

[129] _Mental Physiology_, second edit., p. 172.

[130] _Loc. cit._, p. 390.

[131] This source of error has not escaped the notice of autobiographers themselves. See the remarks of Goethe in the opening passages of his _Wahrheit und Dichtung_.

[132] One wonders whether those persons who, in consequence of an injury to their brain, periodically pass from a normal into an abnormal condition of mind, in each of which there is little or no memory of the contents of the other state, complete their idea of personal continuity in each state by the same kind of process as that described in the text.

[133] The reader will remark that this condition of clear intellectual consciousness, namely, a certain degree of similarity and continuity of character in our successive mental states, is complementary to the other condition, constant change, already referred to. It may, perhaps, be said that all clear consciousness lies between two extremes of excessive sameness and excessive difference.

[134] It follows that any great transformation of our environment may lead to a partial confusion with respect to self. For not only do great and violent changes in our surroundings beget profound changes in our feelings and ideas, but since the idea of self is under one of its aspects essentially that of a relation to not-self, any great revolution in the one term, will confuse the recognition of the other. This fact is expressed in the common expression that we "lose ourselves" when in unfamiliar surroundings, and the process of orientation, or "taking our bearings," fails.

[135] On these disturbances of memory and self-recognition in insanity, see Griesinger, _op. cit._, pp. 49-51; also Ribot, "Des Désordres Généraux de la Mémoire," in the _Revue Philosophique_, August, 1880. It is related by Leuret (_Fragments Psych. sur la Folie_, p. 277) that a patient spoke of his former self as "la personne de moi-même."

[136] In the following account of the process of belief and its errors, I am going over some of the ground traversed by my essay on _Belief, its Varieties and Conditions_ ("Sensation and Intuition," ch. iv.). To this essay I must refer the reader for a fuller analysis of the subject.

[137] For an account of the difference of mechanism in memory and expectation, see Taine, _De l'Intelligence_, 2ième partie, livre premier, ch. ii. sec. 6.

[138] J.S. Mill distinguishes expectation as a radically distinct mode of belief from memory, but does not bring out the contrast with respect to activity here emphasized (James Mill's _Analysis of the Human Mind_, edited by J.S. Mill, p. 411, etc.). For a fuller statement of my view of the relation of belief to action, as compared with that of Professor Bain, see my earlier work.

[139] For some good remarks on the logical aspects of future events as matters of fact, see Mr. Venn's _Logic of Chance_, ch. x.

[140] James Mill's _Analysis of the Human Mind_, edited by J.S. Mill, vol. i p. 414, _et seq._

[141] _Principles of Geology_, ch. iii.

[142] To make this rough analysis more complete, I ought, perhaps, to include the effect of all the errors of introspection, memory, and spontaneous belief, into which the person himself falls, in so far as they communicate themselves to others.

[143] In the case of a vain woman thinking herself much more pretty than others think her, the error is still more obviously one connected with a belief in objective fact.

[144] _The Study of Sociology_, ch. ix.

[145] As a matter of fact, the proportion of accurate knowledge to error is far larger in the case of classes than of individuals. Propositions with general terms for subject are less liable to be faulty than propositions with singular terms for subject.

[146] For a description of each of these extremes of boundless gaiety and utter despondency, see Griesinger, _op. cit._, Bk. III. ch. i. and