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.