“From the surfaces of things,” says Epicurus in the first place, “there passes off a constant stream, which cannot be detected by our senses” (for things would in any other case decrease in size) and which is very fine; “and this because, by reason of the counteracting replenishment, the thing itself in its solidity long preserves the same arrangement and disposition of the atoms; and the motion through the air of these surfaces which detach themselves is of the utmost rapidity, because it is not necessary that what is detached should have any thickness;” it is only a surface. Epicurus says, “Such a conception does not contradict our senses, when we take into consideration how pictures produce their effects in a very similar way, I mean by bringing us into sympathy with external things. Therefore emanations, like pictures, pass out from them into us, so that we see and know the forms and colours of things.”[153] This is a very trivial way of representing sense-perception. Epicurus took for himself the easiest criterion of the truth that is not seen, a criterion still in use, namely that it is not contradicted by what we see or hear. For in truth such matters of thought as atoms, the detachment of surfaces, and so forth, are beyond our powers of sight. Certainly we manage to see and to hear something different; but there is abundance of room for what is seen and what is conceived or imagined to exist alongside of one another. If the two are allowed to fall apart, they do not contradict each other; for it is not until we relate them that the contradiction becomes apparent.

“Error,” as Epicurus goes on to say on the second point “comes to pass when, through the movement that takes place within us on the conception therein wrought, such a change is effected that the conception can no longer obtain for itself the testimony of perception. There would be no truth, no likeness of our perceptions, which we receive as in pictures or in dreams or in any other way, if there were nothing on which we, as it were, put out our faculty of observation. There would be no untruth if we did not receive into ourselves another movement, which, to be sure, is conformable to the entering in of the conception, but which has at the same time an interruption.”[154] Error is therefore, according to Epicurus, only a displacement of the pictures in us, which does not proceed from the movement of perception, but rather from this, that we check their influence by a movement originating in ourselves; how this interruption is brought about will be shown more fully later on (pp. 290, 300).

The Epicurean theory of knowledge reduces itself to these few passages, some of which are also obscurely expressed, or else not very happily selected or quoted by Diogenes Laërtius; it is impossible to have a theory less explicitly stated. Knowledge, on the side of thought, is determined merely as a particular movement which makes an interruption; and as Epicurus, as we have already seen, looks on things as made up of a multitude of atoms, thought is the moment which is different from the atoms, the vacuum, the pores, whereby resistance to this stream of atoms is rendered possible. If this negative is also again, as soul, affirmative, Epicurus in the notional determination of thinking has only reached this negativity, that we look away from something, i.e. we interrupt that inflowing stream. The answer to the question of what this interrupting movement exactly is, when taken for itself, is connected with the more advanced conceptions of Epicurus; and in order to discuss them more in detail, we must go back to the implicit basis of his system.

This constitutes on the whole the metaphysic of Epicurus; in it he has expounded his doctrine of the atom, but not with greater definiteness than did Leucippus and Democritus. The essence and the truth of things were to him, as they were to them, atoms and vacuum: “Atoms have no properties except figure, weight and magnitude.” Atoms, as atoms, must remain undetermined; but the Atomists have been forced to take the inconsistent course of ascribing properties to them: the quantitative properties of magnitude and figure, the qualitative property of weight. But that which is in itself altogether indivisible can have neither figure nor magnitude; and even weight, direction upon something else, is opposed to the abstract repulsion of the atom. Epicurus even says: “Every property is liable to change, but the atoms change not. In all dissolutions of the composite, something must remain a constant and indissoluble, which no change can transform into that which is not, or bring from non-being into Being. This unchangeable element, therefore, is constituted by some bodies and figures. The properties are a certain relation of atoms to each other.”[155] In like manner we have already seen with Aristotle (p. 178) that the tangible is the foundation of properties: a distinction which under various forms is still always made and is in common use. We mean by this that an opposition is established between fundamental properties, such as we here have in weight, figure and magnitude, and sensuous properties, which are only in relation to us, and are derived from the former original differences. This has frequently been understood as if weight were in things, while the other properties were only in our senses: but, in general, the former is the moment of the implicit, or the abstract essence of the thing, while the latter is its concrete existence, which expresses its relation to other things.

The important matter now would be to indicate the relation of atoms to sensuous appearance, to allow essence to pass over into the negative: but here Epicurus rambles amidst the indeterminate which expresses nothing; for we perceive in him, as in the other physicists, nothing but an unconscious medley of abstract ideas and realities. All particular forms, all objects, light, colour, &c., the soul itself even, are nothing but a certain arrangement of these atoms. This is what Locke also said, and even now Physical Science declares that the basis of things is found in molecules, which are arranged in a certain manner in space. But these are empty words, and a crystal, for instance, is not a certain arrangement of parts, which gives this figure. It is thus not worth while to deal with this relation of atoms; for it is an altogether formal way of speaking, as when Epicurus again concedes that figure and magnitude, in so far as pertaining to atoms, are something different from what they are as they appear in things. The two are not altogether unlike; the one, implicit magnitude, has something in common with apparent magnitude. The latter is transitory, variable; the former has no interrupted parts,[156] that is, nothing negative. But the determination of the atoms, as originally formed in this or that fashion, and having original magnitude of such and such a kind, is a purely arbitrary invention. That interruption, which we regarded above (p. 288) as the other side to atoms, or as vacuum, is the principle of movement: for the movement of thought is also like this and has interruptions. Thought in man is the very same as atoms and vacuum are in things, namely their inward essence; that is to say, atoms and vacuum belong to the movement of thought, or exist for this in the same way as things are in their essential nature. The movement of thinking is thus the province of the atoms of the soul; so that there takes place simultaneously therein an interruption of the inward flow of atoms from without. There is therefore nothing further to be seen in this than the general principle of the positive and negative, so that even thought is affected by a negative principle, the moment of interruption. This principle of the Epicurean system, further applied to the difference in things, is the most arbitrary and therefore the most wearisome that can be imagined.

Besides their different figures, atoms have also, as the fundamental mode in which they are affected, a difference of movement, caused by their weight; but this movement to some extent deviates from the straight line in its direction. That is to say, Epicurus ascribes to atoms a curvilinear movement, in order that they may impinge on one another and so on.[157] In this way there arise particular accumulations and configurations; and these are things.

Other physical properties, such as taste and smell, have their basis again in another arrangement of the molecules. But there is no bridge from this to that, or what results is simply empty tautology, according to which the parts are arranged and combined as is requisite in order that their appearance may be what it is. The transition to bodies of concrete appearance Epicurus has either not made at all, or what has been cited from him as far as this matter is concerned, taken by itself, is extremely meagre.

The opinion that one hears expressed respecting the Epicurean philosophy is in other respects not unfavourable; and for this reason some further details must be given regarding it. For since absolute Being is constituted by atoms scattered and disintegrated, and by vacuum, it directly follows that Epicurus denies to these atoms any relationship to one another which implies purpose. All that we call forms and organisms, or generally speaking, the unity of Nature’s end, in his way of thinking, belongs to qualities, to an external connection of the configurations of the atoms, which in this way is merely an accident, brought about by their chance-directed motion; the atoms accordingly form a merely superficial unity, and one which is not essential to them. Or else Epicurus altogether denies that Notion and the Universal are the essential, and because all originations are to him chance combinations, for him their resolution is just as much a matter of chance. The divided is the first and the truly existent, but at the same time chance or external necessity is the law which dominates all cohesion. That Epicurus should in this fashion declare himself against a universal end in the world, against every relation of purpose—as, for instance, the inherent conformity to purpose of the organism—and, further, against the teleological representations of the wisdom of a Creator in the world, his government, &c., is a matter of course; for he abrogates unity, whatever be the manner in which we represent it, whether as Nature’s end in itself, or as end which is in another, but is carried out in Nature. In contrast to this, the teleological view enters largely into the philosophy of the Stoics, and is there very fully developed. To show that conformity to an end is lacking, Epicurus brings forward the most trivial examples; for instance, that worms and so on are produced by chance from mud through the warmth of the sun. Taken in their entirety, they may very well be the work of chance in relation to others; but what is implicit in them, their Notion and essence is something organic: and the comprehension of this is what we have now to consider. But Epicurus banishes thought as implicit, without its occurring to him that his atoms themselves have this very nature of thought; that is, their existence in time is not immediate but essentially mediate, and thus negative or universal;—the first and only inconsistency that we find in Epicurus, and one which all empiricists are guilty of. The Stoics take the opposite course of finding essential Being in the object of thought or the universal; and they fail equally in reaching the content, temporal existence, which, however, they most inconsistently assume. We have here the metaphysics of Epicurus; nothing that he says farther on this head is of interest.

[3. Physics.]

The natural philosophy of Epicurus is based on the above foundation; but an aspect of interest is given it by the fact that it is still peculiarly the method of our times; his thoughts on particular aspects of Nature are, however, in themselves feeble and of little weight, containing nothing but an ill-considered medley of all manner of loose conceptions. Going further, the principle of the manner in which Epicurus looks on nature, lies in the conceptions he forms, which we have already had before us (pp. 282, 285). That is to say, the general representations which we receive through the repetition of several perceptions, and to which we relate such perceptions in forming an opinion, must be then applied to that which is not exactly matter of perception, but yet has something in common with what we can perceive. In this way it comes about that by such images we can apprehend the unknown which does not lend itself immediately to perception; for from what is known we must argue to what is unknown. This is nothing else but saying that Epicurus judged by analogy, or that he makes so-called evidence the principle of his view of Nature; and this is the principle which to this day has authority in ordinary physical science. We go through experiences and make observations, these arising from the sensuous perceptions which are apt to be overlooked. Thus we reach general concepts, laws, forces, and so on, electricity and magnetism, for instance, and these are then applied by us to such objects and activities as we cannot ourselves directly perceive. As an example, we know about the nerves and their connection with the brain; in order that there may be feeling and so on, it is said that a transmission from the finger-tips to the brain takes place. But how can we represent this to ourselves? We cannot make it a matter of observation. By anatomy we can lay bare the nerves, it is true, but not the manner of their working. We represent these to ourselves on the analogy of other phenomena of transmission, for instance as the vibration of a tense string that passes through the nerves to the brain. As in the well-known phenomenon of a number of billiard balls set close together in a row, the last of which rolls away when the first is struck, while those in the middle, through each of which the effect of the stroke has been communicated to the next, scarcely seem to move, so we represent to ourselves the nerves as consisting of tiny balls which are invisible even through the strongest magnifying glass, and fancy that at every touch, &c., the last springs off and strikes the soul. In the same way light is represented as filaments, rays, or as vibrations of the ether, or as globules of ether, each of which strikes on the other. This is an analogy quite in the manner of Epicurus.