CHAPTER X

CONSCIOUSNESS

Consciousness as a Natural Phenomenon--Its Definition--Difficulties of the Problem--Its Relation to the Life of the Soul--Our Human Consciousness--Various Theories: I. Anthropistic Theory (Descartes); II. Neurological Theory (Darwin); III. Animal Theory (Schopenhauer); IV. Biological Theory (Fechner); V. Cellular Theory (Fritz Schultze); VI. Atomistic Theory--Monistic and Dualistic Theories--Transcendental Character of Consciousness--The Ignorabimus Verdict of Du Bois-Reymond--Physiology of Consciousness--Discovery of the Organs of Thought by Flechsig--Pathology--Double and Intermittent Consciousness--Ontogeny of Consciousness: Modifications at Different Ages--Phylogeny of Consciousness--Formation of Concepts

No phenomenon of the life of the soul is so wonderful and so variously interpreted as consciousness. The most contradictory views are current to-day, as they were two thousand years ago, not only with regard to the nature of this psychic function and its relation to the body, but even as to its diffusion in the organic world and its origin and development. It is more responsible than any other psychic faculty for the erroneous idea of an "immaterial soul" and the belief in "personal immortality"; many of the gravest errors that still dominate even our modern civilization may be traced to it. Hence it is that I have entitled consciousness "the central mystery of psychology"; it is the strong citadel of all mystic and dualistic errors, before whose ramparts the best-equipped efforts of reason threaten to miscarry. This fact would suffice of itself to induce us to make a special critical study of consciousness from our monistic point of view. We shall see that consciousness is simply a natural phenomenon like any other psychic quality, and that it is subject to the law of substance like all other natural phenomena.

Even as to the elementary idea of consciousness, its contents and extension, the views of the most distinguished philosophers and scientists are widely divergent. Perhaps the meaning of consciousness is best conceived as an _internal perception_, and compared with the action of _a mirror_. As its two chief departments we distinguish objective and subjective consciousness--consciousness of the world, the non-ego, and of the ego. By far the greater part of our conscious activity, as Schopenhauer justly remarked, belongs to the consciousness of the outer world, or the non-ego: this _world-consciousness_ embraces all possible phenomena of the outer world which are in any sense accessible to our minds. Much more contracted is the sphere of _self-consciousness_, the internal mirror of all our own psychic activity, all our presentations, sensations, and volitions.

Many distinguished thinkers, especially on the physiological side (Wundt and Ziehen, for instance) take the ideas of consciousness and psychic function to be identical--"all psychic action is conscious"; the province of psychic life, they say, is coextensive with that of consciousness. In our opinion, such a definition gives an undue extension to the meaning of consciousness, and occasions many errors and misunderstandings. We share, rather, the view of other philosophers (Romanes, Fritz Schultze, and Paulsen), that even our unconscious presentations, sensations, and volitions pertain to our psychic life; indeed, the province of these unconscious psychic actions (reflex action, and so forth) is far more extensive than that of consciousness. Moreover, the two provinces are intimately connected, and are separated by no sharp line of demarcation. An unconscious presentation may become conscious at any moment; let our attention be withdrawn from it by some other object, and forthwith it disappears from consciousness once more.

The only source of our knowledge of consciousness is that faculty itself; that is the chief cause of the extraordinary difficulty of subjecting it to scientific research. Subject and object are one and the same in it: the perceptive subject mirrors itself in its own inner nature, which is to be the object of our inquiry. Thus we can never have a complete objective certainty of the consciousness of others; we can only proceed by a comparison of their psychic condition with our own. As long as this comparison is restricted to _normal_ people we are justified in drawing certain conclusions as to their consciousness, the validity of which is unchallenged. But when we pass on to consider _abnormal_ individuals (the genius, the eccentric, the stupid, or the insane) our conclusions from analogy are either unsafe or entirely erroneous. The same must be said with even greater truth when we attempt to compare human consciousness with that of the animals (even the higher, but especially the lower). In that case such grave difficulties arise that the views of physiologists and philosophers diverge as widely as the poles on the subject. We shall briefly enumerate the most important of these views.

I. _The anthropistic theory of consciousness._--It is peculiar to man. To Descartes we must trace the widespread notion that consciousness and thought are man's exclusive prerogative, and that he alone is blessed with an "immortal soul." This famous French philosopher and mathematician (educated in a Jesuit College) established a rigid partition between the psychic activity of man and that of the brute. In his opinion the human soul, a thinking, immaterial being, is completely separated from the body, which is extended and material. Yet it is united to the body at a certain point in the brain (the _glandula pinealis_) for the purpose of receiving impressions from the outer world and effecting muscular movements. The animals, not being endowed with thought, have no soul: they are mere automata, or cleverly constructed machines, whose sensations, presentations, and volitions are purely mechanical, and take place according to the ordinary laws of physics. Hence Descartes was a _dualist_ in human psychology, and a _monist_ in the psychology of the brute. This open contradiction in so clear and acute a thinker is very striking; in explaining it, it is not unnatural to suppose that he concealed his real opinion, and left the discovery of it to independent scholars. As a pupil of the Jesuits, Descartes had been taught to deny the truth in the face of his better insight; and perhaps he dreaded the power and the fires of the Church. Besides, his sceptical principle, that every sincere effort to attain the truth must start with a doubt of the traditional dogma had already drawn upon him fanatical accusations of scepticism and atheism. The great influence which Descartes had on subsequent philosophy was very remarkable, and entirely in harmony with his "book-keeping by double entry." The _materialists_ of the seventeenth and eighteenth centuries appealed to the Cartesian theory of the animal soul and its purely mechanical activity in support of their monistic psychology. The _spiritualists_, on the other hand, asserted that their dogma of the immortality of the soul and its independence of the body was firmly established by Descartes' theory of the human soul. This view is still prevalent in the camp of the theologians and dualistic metaphysicians. The scientific conception of nature, however, which has been built up in the nineteenth century, has, with the aid of empirical progress, in physiological and comparative psychology, completely falsified it.

II. _Neurological theory of consciousness._--It is present only in man and those higher animals which have a centralized nervous system and organs of sense. The conviction that a large number of animals--at least the higher mammals--are not less endowed than man with a thinking soul and consciousness prevails in modern zoology, exact physiology, and the monistic psychology. The immense progress we have made in the various branches of biology has contributed to bring about a recognition of this important truth. We confine ourselves for the present to the higher vertebrates, and especially the mammals. That these most intelligent specimens of these highly developed vertebrates--apes and dogs, in particular--have a strong resemblance to man in their whole psychic life has been recognized and speculated on for thousands of years. Their faculty of presentation and sensation, of feeling and desire, is so like that of man that we need adduce no proof of our thesis. But even the higher associational activity of the brain, the formation of judgments and their connection into chains of reasoning, thought, and consciousness in the narrower sense, are developed in them after the same fashion as in man: they differ only in degree, not in kind. Moreover, we learn from comparative anatomy and histology that the intricate structure of the brain (both in general and in detail) is substantially the same in the mammals as it is in man. The same lesson is enforced by comparative ontogeny with regard to the origin of these psychic organs. Comparative physiology teaches us that the various states of consciousness are just the same in these highest placentals as in man; and we learn by experiment that there is the same reaction to external stimuli. The higher animals can be narcotized by alcohol, chloroform, ether, etc., and may be hypnotized by the usual methods, just as in the case of man.

It is, however, impossible to determine mathematically at what stage of animal life consciousness is to be first recognized as such. Some zoologists draw the line very high in the scale, others very low. Darwin, who most accurately distinguishes the various stages of consciousness, intelligence, and emotion in the higher animals, and explains them by progressive evolution, points out how difficult, or even impossible, it is to determine the first beginning of this supreme psychic faculty in the lower animals. Personally, out of the many contradictory theories, I take that to be most probable which holds _the centralization of the nervous system_ to be a condition of consciousness; and that is wanting in the lower classes of animals. The presence of a central nervous organ, of highly developed sense-organs, and an elaborate association of groups of presentations, seem to me to be required before the unity of consciousness is possible.

III. _Animal theory of consciousness._--All animals, and they alone, have consciousness. This theory would draw a sharp distinction between the psychic life of the animal and of the plant. Such a distinction was urged by many of the older writers, and was clearly formulated by Linné in his celebrated _Systema Naturae_; the two great kingdoms of the organic world are, in his opinion, divided by the fact that animals have sensation and consciousness, and the plants are devoid of them. Later on Schopenhauer laid stress on the same distinction: "Consciousness is only known to us as a feature of animal nature. Even though it extend upwards through the whole animal kingdom, even to man and his reason, the unconsciousness of the plant, from which it started, remains as the basic feature. In the lowest animals we have but the dawn of it." The inaccuracy of this view was obvious by about the middle of the present century, when a deeper study was made of the psychic activity of the lower animal forms, especially the coelenterates (sponges and cnidaria): they are undoubtedly animals, yet there is no more trace of a definite consciousness in them than in most of the plants. The distinction between the two kingdoms was still further obliterated when more careful research was made into their unicellular forms. There is no psychological difference between the plasmophagous protozoa and the plasmodomous protophyta, even in respect of their consciousness.

IV. _Biological theory of consciousness._--It is found in all organisms, animal or vegetal, but not in lifeless bodies (such as crystals). This opinion is usually associated with the idea that all organisms (as distinguished from inorganic substances) have souls: the three ideas--life, soul, and consciousness--are then taken to be coextensive. Another modification of this view holds that, though these fundamental phenomena of organic life are inseparably connected, yet consciousness is only a part of the activity of the soul, and of the vital activity. Fechner, in particular, has endeavored to prove that the plant has a "soul," in the same sense as an animal is said to have one; and many credit the vegetal soul with a consciousness similar to that of the animal soul. In truth, the remarkable stimulated movements of the leaves of the sensitive plants (the mimosa, drosera, and dionæa), the automatic movements of other plants (the clover and wood-sorrel, and especially the hedysarum), the movements of the "sleeping plants" (particularly the _papilionacea_), etc., are strikingly similar to the movements of the lower animal forms: whoever ascribes consciousness to the latter cannot refuse it to such vegetal forms.

V. _Cellular theory of consciousness._--It is a vital property of every cell. The application of the cellular theory to every branch of biology involved its extension to psychology. Just as we take the living cell to be the "elementary organism" in anatomy and physiology, and derive the whole system of the multicellular animal or plant from it, so, with equal right, we may consider the "cell-soul" to be the psychological unit, and the complex psychic activity of the higher organism to be the result of the combination of the psychic activity of the cells which compose it. I gave the outlines of this _cellular psychology_ in my _General Morphology_ in 1866, and entered more fully into the subject in my paper on "Cell-Souls and Soul-Cells." I was led to a deeper study of this "elementary psychology" by my protracted research into the unicellular forms of life. Many of these tiny (generally microscopic) protists show similar expressions of sensation and will, and similar instincts and movements, to those of higher animals; that is especially true of the very sensitive and lively infusoria. In the relation of these sensitive cell-organisms to their environment, and in many other of their vital expressions (for instance, in the wonderful architecture of the rhizopods, the thalamophoræ, and the infusoria), we seemed to have clear indications of conscious psychic action. If, then, we accept the biological theory of consciousness (No. IV.), and credit every psychic function with a share of that faculty, we shall be compelled to ascribe it to each independent protist cell. In that case its material basis would be either the entire protoplasm of the cell, or its nucleus, or a portion of it. In the "psychade theory" of Fritz Schultze the elementary consciousness of the _psychade_ would have the same relation to the individual cells as personal consciousness has to the multicellular organism of the personality in the higher animals and man. It is impossible definitively to disprove this theory, which I held at one time. Still, I now feel compelled to agree with Max Verworn, in his belief that none of the protists have a developed self-consciousness, but that their sensations and movements are of an unconscious character.

VI. _Atomistic theory of consciousness._--It is an elementary property of all atoms. This atomistic hypothesis goes furthest of all the different views as to the extension of consciousness. It certainly escapes the difficulty which so many philosophers and biologists experience in solving the problem of the first origin of consciousness. It is a phenomenon of so peculiar a character that a derivation of it from other psychic functions seems extremely hazardous. It seemed, therefore, the easiest way out of the difficulty to conceive it as an inherent property of all matter, like gravitation or chemical affinity. On that hypothesis there would be as many forms of this original consciousness as there are chemical elements; each atom of hydrogen would have its hydrogenic consciousness, each atom of carbon its carbonic consciousness, and so forth. There are philosophers, even, who ascribe consciousness to the four elements of Empedocles, the union of which, by "love and hate," produces the totality of things.

Personally, I have never subscribed to this hypothesis of atomic consciousness. I emphasize the point because Emil du Bois-Reymond has attributed it to me. In the controversy I had with him (1880) he violently attacked my "pernicious and false philosophy," and contended that I had, in my paper on "The Perigenesis of the Plastidule," "laid it down as a metaphysical axiom that every atom has its individual consciousness." On the contrary, I explicitly stated that I conceive the elementary psychic qualities of sensation and will, which may be attributed to atoms, to be _unconscious_--just as unconscious as the elementary memory which I, in company with that distinguished physiologist, Ewald Hering, consider to be "a common function of all organized matter"--or, more correctly, "living substance." Du Bois-Reymond curiously confuses "soul" and "consciousness"; whether from oversight or not I cannot say. Since he considers consciousness to be a transcendental phenomenon (as we shall see presently), while denying that character to other psychic functions--the action of the senses, for example--I must infer that he recognizes the difference of the two ideas. Other parts of his eloquent speeches contain quite the opposite view, for the famous orator not infrequently contradicts himself on important questions of principle. However, I repeat that, in my opinion, consciousness is only _part_ of the psychic phenomena which we find in man and the higher animals; the great majority of them are unconscious.

However divergent are the different views as to the nature and origin of consciousness, they may, nevertheless, on a clear and logical examination, all be reduced to two fundamental theories--the transcendental (or dualistic) and the physiological (or monistic). I have myself always held the latter view, in the light of my evolutionary principles, and it is now shared by a great number of distinguished scientists, though it is by no means generally accepted. The transcendental theory is the older and much more common; it has recently come once more into prominence, principally through Du Bois-Reymond, and it has acquired a great importance in modern discussions of cosmic problems through his famous "Ignorabimus speech." On account of the extreme importance of this fundamental question we must touch briefly on its main features.

In the celebrated discourse on "The Limits of Natural Science," which E. du Bois-Reymond gave on August 14, 1872, at the Scientific Congress at Leipzig, he spoke of two "absolute limits" to our possible knowledge of nature which the human mind will never transcend in its most advanced science--_never_, as the oft-quoted termination of the address, "Ignorabimus," emphatically pronounces. The first absolutely insoluble "world-enigma" is the "connection of matter and force," and the distinctive character of these fundamental natural phenomena; we shall go more fully into this "problem of substance" in the twelfth chapter. The second insuperable difficulty of philosophy is given as the problem of consciousness--the question how our mental activity is to be explained by material conditions, especially movements, how "substance [the substance which underlies matter and force] comes, under certain conditions, to feel, to desire, and to think."

For brevity, and in order to give a characteristic name to the Leipzig discourse, I have called it the "Ignorabimus speech"; this is the more permissible, as E. du Bois-Reymond himself, with a just pride, eight years afterwards, speaking of the extraordinary consequences of his discourse, said: "Criticism sounded every possible note, from friendly praise to the severest censure, and the word 'Ignorabimus,' which was the culmination of my inquiry, was at once transformed into a kind of scientific shibboleth." It is quite true that loud praise and approbation resounded in the halls of the dualistic and spiritualistic philosophy, and especially in the camp of the "Church militant"; even the spiritists and the host of believers, who thought the immortality of their precious souls was saved by the "Ignorabimus," joined in the chorus. The "severest censure" came at first only from a few scientists and philosophers--from the few who had sufficient scientific knowledge and moral courage to oppose the dogmatism of the all-powerful secretary and dictator of the Berlin Academy of Science.

Towards the end, however, the author of the "Ignorabimus speech" briefly alluded to the question whether these two great "world-enigmas," the general problem of substance and the special problem of consciousness, are not two aspects of one and the same problem. "This idea," he said, "is certainly the simplest, and preferable to the one which makes the world doubly incomprehensible. Such, however, is the nature of things that even here we can obtain no clear knowledge, and it is useless to speak further of the question." The latter sentiment I have always stoutly contested, and have endeavored to prove that the two great questions are not two distinct problems. "The neurological problem of consciousness is but a particular aspect of the all-pervading cosmological problem of substance."

The peculiar phenomenon of consciousness is not, as Du Bois-Reymond and the dualistic school would have us believe, a completely "transcendental" problem; it is, as I showed thirty-three years ago, a _physiological_ problem, and, as such, must be reduced to the phenomena of physics and chemistry. I subsequently gave it the more definite title of a _neurological_ problem, as I share the view that true consciousness (thought and reason) is only present in those higher animals which have a centralized nervous system and organs of sense of a certain degree of development. Those conditions are certainly found in the higher vertebrates, especially in the placental mammals, the class from which man has sprung. The consciousness of the highest apes, dogs, elephants, etc., differs from that of man in degree only, not in kind, and the graduated interval between the consciousness of these "rational" placentals and that of the lowest races of men (the Veddahs, etc.) is less than the corresponding interval between these uncivilized races and the highest specimens of thoughtful humanity (Spinoza, Goethe, Lamarck, Darwin, etc.). Consciousness is but a part of the higher activity of the soul, and as such it is dependent on the normal structure of the corresponding psychic organ, the brain.

Physiological observation and experiment determined twenty years ago that the particular portion of the mammal-brain which we call the _seat_ (preferably the _organ_) of consciousness is a part of the cerebrum, an area in the late-developed gray bed, or cortex, which is evolved out of the convex dorsal portion of the primary cerebral vesicle, the "fore-brain." Now, the morphological proof of this physiological thesis has been successfully given by the remarkable progress of the microscopic anatomy of the brain, which we owe to the perfect methods of research of modern science (Kölliker, Flechsig, Golgi, Edinger, Weigert, and others).

The most important development is the discovery of the _organs of thought_ by Paul Flechsig, of Leipzig; he proved that in the gray bed of the brain are found the four seats of the central sense-organs, or four "inner spheres of sensation"--the sphere of touch in the vertical lobe, the sphere of smell in the frontal lobe, the sphere of sight in the occipital lobe, and the sphere of hearing in the temporal lobe. Between these four "sense-centres" lie the four great "thought-centres," or centres of association, the _real organs of mental life_; they are those highest instruments of psychic activity that produce thought and consciousness. In front we have the frontal brain or centre of association; behind, on top there is the vertical brain, or parietal centre of association, and underneath the principal brain, or "the great occipito-temporal centre of association" (the most important of all); lower down, and internally, the insular brain or the insula of Reil, the insular centre of association. These four "thought-centres," distinguished from the intermediate "sense-centres" by a peculiar and elaborate nerve-structure, are the true and sole organs of thought and consciousness. Flechsig has recently pointed out that, in the case of man, very specific structures are found in one part of them; these structures are wanting in the other mammals, and they, therefore, afford an explanation of the superiority of man's mental powers.

The momentous announcement of modern physiology, that the cerebrum is the organ of consciousness and mental action in man and the higher mammals, is illustrated and confirmed by the pathological study of its diseases. When parts of the cortex are destroyed by disease their respective functions are affected, and thus we are enabled, to some extent, to localize the activities of the brain; when certain parts of the area are diseased, that portion of thought and consciousness disappears which depends on those particular sections. Pathological experiment yields the same result; the decay of some known area (for instance, the centre of speech) extinguishes its function (speech). In fact, there is proof enough in the most familiar phenomena of consciousness of their complete dependence on chemical changes in the substance of the brain. Many beverages (such as coffee and tea) stimulate our powers of thought; others (such as wine and beer) intensify feeling; musk and camphor reanimate the fainting consciousness; ether and chloroform deaden it, and so forth. How would that be possible if consciousness were an immaterial entity, independent of these anatomical organs? And what becomes of the consciousness of the "immortal soul" when it no longer has the use of these organs?

These and other familiar facts prove that man's consciousness--and that of the nearest mammals--is _changeable_, and that its activity is always open to modification from inner (alimentation, circulation, etc.) and outer causes (lesion of the brain, stimulation, etc.). Very instructive, too, are the facts of double and intermittent consciousness, which remind us of "alternate generations of presentations." The same individual has an entirely different consciousness on different days, with a change of circumstances; he does not know to-day what he did yesterday: yesterday he could say, "I am I"; to-day he must say, "I am another being." Such intermittence of consciousness may last not only days, but months, and even years; the change may even become permanent.

As everybody knows, the new-born infant has no consciousness. Preyer has shown that it is only developed after the child has begun to speak; for a long time it speaks of itself in the third person. In the important moment when it first pronounces the word "I," when the feeling of self becomes clear, we have the beginning of self-consciousness, and of the antithesis to the non-ego. The rapid and solid progress in knowledge which the child makes in its first ten years, under the care of parents and teachers, and the slower progress of the second decade, until it reaches complete maturity of mind, are intimately connected with a great advancement in the growth and development of consciousness and of its organ, the brain. But even when the pupil has got his "certificate of maturity" his consciousness is still far from mature; it is then that his "world-consciousness" first begins to develop, in his manifold relations with the outer world. Then, in the third decade, we have the full maturity of rational thought and consciousness, which, in cases of normal development, yield their ripe fruits during the next three decades. The slow, gradual degeneration of the higher mental powers, which characterizes senility, usually sets in at the commencement of the seventh decade--sometimes earlier, sometimes later. Memory, receptiveness, and interest in particular objects gradually decay; though productivity, mature consciousness, and philosophic interest in general truths often remain for many years longer.

The individual development of consciousness in earlier youth proves the universal validity of the _biogenetic law_; and, indeed, it is still recognizable in many ways during the later years. In any case, the ontogenesis of consciousness makes it perfectly clear that it is not an "immaterial entity," but a physiological function of the brain, and that it is, consequently, no exception to the general law of substance.

From the fact that consciousness, like all other psychic functions, is dependent on the normal development of certain organs, and that it gradually unfolds in the child in proportion to the development of those organs, we may already conclude that it has arisen in the animal kingdom by a gradual historical development. Still, however certain we are of the fact of this natural evolution of consciousness, we are, unfortunately, not yet in a position to enter more deeply into the question and construct special hypotheses in elucidation of it. Palæontology, it is true, gives us a few facts which are not without significance. For instance, the quantitative and qualitative development of the brain of the placental mammals during the Tertiary period is very remarkable. The cavity of many of the fossil skulls of the period has been carefully examined, and has given us a good deal of reliable information as to the size, and, to some extent, as to the structure, of the brain they enclosed. We find, within the limits of one and the same group (the ungulates, the rodents, or the primates), a marked advance in the later miocene and pliocene specimens as compared with the earlier eocene and oligocene representatives of the same stem; in the former the brain (in proportion to the size of the organism) is six to eight times as large as in the latter.

Moreover, that highest stage of consciousness, which is reached by man alone, has been evolved step by step--even by the very progress of civilization--from a lower condition, as we find illustrated to-day in the case of uncivilized races. That is easily proved by a comparison of their languages, which is closely connected with the comparison of their ideas. The higher the conceptual faculty advances in thoughtful civilized man, the more qualified he is to detect common features amid a multitude of details, and embody them in general concepts, and so much the clearer and deeper does his consciousness become.