This Dialogue contains the first intimation of the doctrine of reminiscence and of the immortality of the soul. The proof is very slight, even slighter than in the Phaedo and Republic. Because men had abstract ideas in a previous state, they must have always had them, and their souls therefore must have always existed. For they must always have been either men or not men. It may be observed, however, that the fanciful notion of pre-existence is combined with a true but partial view of the origin and unity of knowledge, and of the association of ideas. Knowledge is prior to any particular knowledge, and exists not in the previous state of the individual, but of the race. It is potential, not actual, and can only be appropriated by strenuous exertion. The idealism of Plato is here presented in a less developed form than in the Phaedo and Phaedrus. Nothing is said of the pre-existence of ideas of justice, temperance, and the like. Nor is Socrates positive of anything but the duty of enquiry. The doctrine of reminiscence too is explained more in accordance with fact and experience as arising out of the affinities of nature (ate tes thuseos oles suggenous ouses). Modern philosophy says that all things in nature are dependent on one another; the ancient philosopher had the same truth latent in his mind when he affirmed that out of one thing all the rest may be recovered.