When we read the explanations given by Epikurus and Lucretius of what the Epikurean theory really was, and compare them with the numerous attacks upon it made by opponents, we cannot but remark that the title and formula of the theory was ill-chosen, and really a misnomer. What Epikurus meant by Pleasure was not what most people meant by it, but something very different — a tranquil and comfortable state of mind and body; much the same as what Demokritus had expressed before him by the phrase εὐθυμία. This last phrase would have expressed what Epikurus aimed at, neither more nor less. It would at least have preserved his theory from much misplaced sarcasm and aggressive rhetoric.
The Physics of Epikurus was borrowed in the main from the atomic theory of Demokritus, but modified by him in a manner subservient and contributory to his ethical scheme. To that scheme it was essential that those celestial, atmospheric, or terrestrial phenomena which the public around him ascribed to agency and purposes of the gods, should be understood as being produced by physical causes. An eclipse, an earthquake, a storm, a shipwreck, unusual rain or drought, a good or a bad harvest — and not merely these, but many other occurrences far smaller and more unimportant, as we may see by the eighteenth chapter of the ‘Characters’ of Theophrastus — were then regarded as visitations of the gods, requiring to be interpreted by recognized prophets, and to be appeased by ceremonial expiations. When once a man became convinced that all these phenomena proceeded from physical agencies, a host of terrors and anxieties would disappear from the mind; and this Epikurus asserted to be the beneficent effect and real recommendation of physical philosophy. He took little or no thought for scientific curiosity as a motive per se, which both Demokritus and Aristotle put so much in the foreground.
He composed a treatise called ‘Kanonicon’ (now lost), which seems to have been a sort of Logic of Physics — a summary of the principles of evidence. In his system, Psychology was to a great extent a branch — though a peculiar and distinct branch — of Physics, since the soul was regarded as a subtle but energetic material compound (air, vapour, heat, and another nameless ingredient), with its best parts concentrated in the chest, yet pervading and sustaining the whole body — still, however, depending for its support on the body, and incapable of separate or disembodied continuance.
Epikurus recognized, as the primordial basis of the universe, Atoms, Vacuum, and Motion. The atoms were material solid minima, each too small to be apprehended separately by sense; they had figure, magnitude, and gravity, but no other qualities. They were infinite in number, and ever moving in an infinite vacuum. Their motions brought them into various coalitions and compounds, resulting in the perceptible bodies of nature; each of which in its combined state acquired new, specific, different qualities. In regard to the primordial movements of the atoms, out of which these endowed compounds grew, Epikurus differed from Demokritus who supposed the atoms originally to move with an indefinite variety of directions and velocities, rotatory as well as rectilineal; whereas Epikurus maintained that the only original movement common to all atoms was one and the same — in the direction of gravity straight down, and all with equal velocity in the infinite void. But it occurred to him that, upon this hypothesis only, there could never occur any collisions or combinations of the atoms — nothing but continued and unchangeable parallel lines. Accordingly he modified it by saying that the line of descent was not strictly rectilinear, but that each atom deflected a little from the straight line, each in its own direction and degree; so that it became possible to assume collisions, resiliences, adhesions, combinations, among them, as it had been possible under the variety of original movements ascribed to them by Demokritus. The opponents of Epikurus derided this auxiliary hypothesis, affirming that he invented the individual deflection of each atom without assigning any cause, and only because he was perplexed by the mystery of man’s freewill. But Epikurus was not more open to attack on this ground than other physical philosophers. Most of them (except perhaps the most consistent of the Stoic fatalists) believed that some among the phenomena of the universe occurred in regular and predictable sequence, while others were essentially irregular and unpredictable: each philosopher devised his hypothesis, and recognized some fundamental principle, to explain the latter class of phenomena as well as the former; thus, Plato admitted an invincible erratic necessity, Aristotle introduced Chance and Spontaneity, Demokritus multiplied indefinitely the varieties of atomic movements. The hypothetical deflection alleged by Epikurus was his way, not more unwarranted than the others, of providing a fundamental principle for the unpredictable phenomena of the universe. Among these are the volitional manifestations of men and animals; but there are many others besides, and there is no ground for believing that what is called the mystery of Free-Will (i. e., the question whether volition is governed by motives, acting upon a given state of the mind and body) was at all peculiarly present to his mind. Whatever theory may be adopted on this point, it is certain that the movements of an individual man or animal are not exclusively determined by the general law of gravitation, or by another cause extrinsic to himself; but to a great degree by his own separate volition, which is often imperfectly knowable beforehand and therefore not predictable. For these and many other phenomena, Epikurus provided a fundamental principle in his supplementary hypothesis of atomic deflection; and indeed not for these only, but also for the questions of opponents, how there could ever be any coalition between the atoms, if all followed only one single law of movement — rectilineal descent with equal velocity. Epikurus rejected the inexorable and all-comprehensive fatalism contained in the theories of some Stoics, though seemingly not construed in its full application even by them. He admitted a limited range of empire to Chance, or phenomena essentially irregular. But he maintained that the will, far from being among the phenomena essentially irregular, is under the influence of motives; for no man can insist more strenuously than he does (see the letter to Menœkeus) on the complete power of philosophy — if the student could be made to feel its necessity and desire the attainment of it, so as to meditate and engrain within himself sound views about the gods, death, and human life generally — to mould our volitions and character in a manner conformable to the exigencies of virtue and happiness.
All true belief, according to Epikurus, rested ultimately upon the impressions of sense, upon our internal feelings, and upon our correct apprehension of the meaning of terms. He did not suppose the significance of language to come by convention, but to be an inspiration of Nature, different among different people. The facts of sense were in themselves beyond all question. But truth, though founded upon these evidences, included various inferences, more than sense could directly testify. Even the two capital points of the Epikurean physical philosophy — Atoms and Void — were inferences from sense, and not capable of direct attestation. It was in these inferences, and in the superstructure built upon sense, that error was so frequently imposed upon us. We ought to test all affirmations or dogmas by the evidence of sensible phenomena; looking therein, if possible, for some positive grounds in support of them, but at any rate assuring ourselves that there were no grounds in contradiction of them, or, if there were such, rejecting the dogmas at once. Out of the particular impressions of sense, when often repeated, remembered, and compared, there grew certain general notions or anticipations (προλήψεις), which were applied to interpret or illustrate any new case when it arose. These general notions were not inborn or intuitive, but gradually formed (as Aristotle and the Stoics also conceived them) out of frequent remembrances and association.
Besides those conclusions which could be fully proved by the evidentiary data just enumerated, Epikurus recognized admissible hypotheses, which awaited farther evidence confirmative or refutative (τὸ πρόσμενον), and also other matters occult or as yet unexplained (τὰ ἄδηλα). Along with the intermediate or half-explained class, he reckoned those in which plurality of causes was to be invoked. A given effect might result from any one out of two, three, or more different causes, and there was often no counter-evidence of sense to exclude either of them in any particular case. This plural explanation (τὸ πλεοναχῶς) was not so complete or satisfactory as the singular (τὸ μοναχῶς); but it was often the best that we could obtain, and was quite sufficient, by showing a possible physical agency, to rescue the mind from those terrors of ignorance, which drove men to imagine visitations of the gods.
Epikurus agreed with Demokritus in believing that external objects produced their impressions on our senses by projecting thin images, outlines of their own shapes. He thought that the air was peopled with such images, which passed through it and still more through the infinite vacuum beyond it with prodigious velocity. Many of them became commingled, dissipated, recombined, during the transit, so that, when they reached us, the impressions produced were not conformable to any real object; hence the phenomena of dreams, madness, and the various delusions of waking men.
In setting forth the criterion of truth, Epikurus insisted chiefly upon the fundamental groundwork — particular facts of sense, as the data for proving or disproving general affirmations; and he had the merit of calling attention to refutative data as well as to probative. But, respecting the process of passing from these particulars to true generalities and avoiding the untrue, we can make out no clear idea from his writings that remain: his great work on Physical Philosophy is lost. It is certain that he disregarded the logical part of the process — the systematic study of propositions, and their relations of consistency with one another — which had made so prodigious a stride during his early years under Aristotle and Theophrastus. We can, indeed, detect in his remaining sentences one or two of those terms which Aristotle had stamped as technical in Logic; but he discouraged as useless all the verbal teaching and discussion of his day — all grammar, rhetoric, and dialectic, beyond the lowest minimum. He disapproved of the poets as promulgators of mischievous fables and prejudices, the rhetoricians as furnishing weapons for the misleading career of political ambition, the dialecticians as wasting their time in useless puzzles. None of them were serviceable in promoting either the tranquillity of the mind, or the happiness of life, or the acquisition of truth. He himself composed a great number of treatises and epistles, on subjects of ethics and philosophy; but he is said to have written in haste, without taking time or trouble to correct his compositions. By the Alexandrine critic, Aristophanes of Byzantium, his style was censured as unpolished; yet it is declared to have been simple, unaffected, and easily understood. This last predicate is hardly applicable to the three epistles which alone remain from his pen; but those epistles are intended as brief abstracts of doctrine, on topics which he had already treated at length in formal works; and it is not easy to combine clearness with brevity.