What Democritus hoped to get by this double or correlative system was a means of accounting for or conceiving of _change_ in nature. The difficulty with the Eleatics was, as we have seen, how to understand whence or why the transition from that which absolutely is, to this strange, at least apparent, system of eternal flux and transformation. Democritus { 76} hoped to get over this difficulty by starting as fully with that which _is not_, in other words, with that which _wants_ change in order to have any recognisable being at all, as with that which _is_, and which therefore might be conceived as seeking and requiring only to be what it is.
Having got his principle of stability and his principle of change on an equal footing, Democritus next laid it down that all the differences visible in things were differences either of shape, of arrangement, or of position; practically, that is, he considered that what seem, to us to be qualitative differences in things, _e.g._ hot or cold, sweet or sour, green or yellow, are only resulting impressions from different shapes, or different arrangements, or different modes of presentation, among the atoms of which things are composed.
Coming now to that which _is_, Democritus, as against the Eleatics, maintained that this was not a unity, some one immovable, unchangeable existence, but an innumerable number of atoms, invisible by reason of their smallness, which career through empty space (that which _is not_), and by their union bring objects into being, by their separation bring these to destruction. The action of these atoms on each other depended on the manner in which they were brought into contact; but in any case the unity of any object was only an apparent unity, it being really constituted of a multitude of interlaced and mutually related { 77} particles, and all growth or increase of the object being conditioned by the introduction into the structure of additional atoms from without.
For the motions of the atoms he had no anterior cause to offer, other than necessity or fate. They existed, and necessarily and always had existed, in a state of whirl; and for that which always had been he maintained that no preceding cause could legitimately or reasonably be demanded.