Book iv shows how the impressions made upon our senses are caused by

minute images detached from the objects about us. We see, for instance, because minute images of the object seen strike our eyes. Dreams and love are also treated in this book. In Book v the origin of the earth, sun, moon, and stars is described, the beginning of life is explained, and the progress of civilization, from the time when men were savages, is depicted. Some passages in this book anticipate in a measure the modern doctrine of the survival of the fittest. Since our world was not created, but came into being naturally by the combinations of atoms, it will also come to an end at some time by the separation of the atoms. In Book vi various striking phenomena are treated, such as thunder, lightning, earthquakes, tempests, and volcanoes. The book ends with a description of the plague at Athens, derived from the account of Thucydides.

[Sidenote: Ethical doctrine.] Since the main purpose of the poem is to free men from religion and the fear of death by showing that all things, including the soul, came into being and are to pass away without any action of the gods, ethical doctrines are not systematically treated. Lucretius accepts, however, the Epicurean dogma that pleasure is the chief good, “the guide of life,”[23] but the pleasure he has in mind is not the common physical pleasure, but the calm repose of the philosopher:

Oh wretched minds of men, oh blinded hearts! Within what shades of life and dangers great Is passed whate’er of age we have! Dost thou Not see that nature makes demand for naught Save this, that pain be absent from our frame, That she, removed from care at once and fear, May have her pleasure in the joys of mind?[24]

Again, in the splendid praise of Epicurus, which opens the fifth book, he says that we may live without grain or wine,

But well one can not live without pure heart.[25]

The only Greek philosophers, besides Epicurus, of whom Lucretius speaks in terms of praise are Democritus, from whom Epicurus borrowed the atomic theory, and Empedocles. Perhaps Lucretius imitates in his work the poem of Empedocles, which bore the same title. At any rate, Empedocles was a man of exalted modes of thought and dignified, poetic expression, qualities which would naturally awaken admiration in the mind of Lucretius. [Sidenote: His reading, observation, and love of nature.] That Lucretius was well acquainted with the great works of Greek literature and with the writings of Nævius, Ennius, Pacuvius, Lucilius, and Accius, is evident from direct references to them, or imitations of them. But he was not merely a student of books. His power of observation and his love of nature are shown in many passages, as where he describes the raging winds and rivers,[26] the life and motion of an army,[27] the striking features of the island of Sicily,[28] the echo in the mountains,[29] or pleasant repose under a shady tree on the grass by the river side.[30]

[Sidenote: Two famous passages.] The poem opens with an invocation to Venus, which is justly famous. The first lines are:

Goddess from whom descends the race of Rome, Venus, of earth and heaven supreme delight, Hail, thou that all beneath the starry dome— Lands rich with grain and seas with navies white— Blessest and cherishest! Where thou dost come Enamelled earth decks her with posies bright To meet thy advent; clouds and tempests flee, And joyous light smiles over land and sea.[31]

Another famous passage is the beginning of Book ii, which has been translated into English hexameters as follows:

Sweet, when the great sea’s water is stirred to its depth by the storm winds, Standing ashore to descry one afar off mightily struggling; Not that a neighbor’s sorrow to you yields dulcet enjoyment; But that the sight hath a sweetness, of ills ourselves are exempt from. Sweet ’tis too to behold, on a broad plain mustering war-hosts Arm them for some great battle, one’s self unscathed by the danger; Yet still happier this: To possess, impregnably guarded, Those calm heights of the sages which have for an origin Wisdom; Thence to survey our fellows, observe them this way and that way Wander amid Life’s paths, poor stragglers seeking a highway; Watch mind battle with mind, and escutcheon rival escutcheon; Gaze on that untold strife, which is waged ’neath the sun and the starlight, Up as they toil on the surface whereon rest Riches and Empire.[32]

Lucretius was perfectly aware that his subject was not an easy one to treat in verse, but was confident of his own power. His work shows that his confidence was justified. Yet even he could not, in explaining the details of the philosophy of Epicurus, move always in the upper realms of poetry. [Sidenote: Style.] The result is that the poem is uneven. In parts it rises to heights hardly attained by any other Latin author, but in other parts long passages are dull and monotonous. Yet even in these parts the verses have a serious, dignified music, the language is carefully chosen, and the subject is treated with consistency, clearness, and vigor. In the more animated portions of his work, Lucretius speaks almost like an inspired prophet. His thought hurries his lines along with increasing impetus, until their flow seems almost irresistible. Strength, rapidity, and power are the most striking features of his style. Minor elements are frequent assonances of various kinds, such as alliteration, repetition, the use of two or more words from one root, and the like, elaborate similes, and occasionally the form of direct address. With all these, the style is characterized by an austere dignity.

In his discussion of the development of the universe, and especially in the part dealing with living creatures, man, and the progress of civilization, Lucretius expresses conclusions not unlike some of those reached in our own day by modern science. [Sidenote: Anticipation of modern science.] But his processes are not scientific. He reasons, to be sure, from concrete facts to theories and from theories again to concrete facts, but the method of his reasoning is unlike that of modern science. Lucretius, like other philosophers of ancient times, having once accepted a theory which explains certain phenomena, makes his theory the rule by which all phenomena are to be measured and in accordance with which they are to be understood. It is interesting to note that Lucretius, following Democritus and Epicurus, anticipates to a certain extent the modern atomic theory, the theories of the evolution of species, of the survival of the fittest, and of the continual progress of mankind from a condition of savagery to civilization, but his conclusions are reached, not by the patient toil of modern scientific research, but by abstract theorizing, to which his poetic imagination gives vividness and almost convincing power.

The greatness of Lucretius as a poet has always been recognized by critical readers; but he has never been a popular author. His subject is too abstruse and his style too austere and dignified to appeal to the taste of the masses, which probably accounts for the fact that his poem has come down to us through only one copy, from which all the existing manuscripts are derived.