The Euthydemus, though apt to be regarded by us only as an elaborate jest, has also avery serious purpose. It may fairly claim to be the oldest treatise on logic; for that scienceoriginates in the misunderstandings which necessarily accompany the first efforts ofspeculation. Several of the fallacies which are satirized in it reappear in the SophisticiElenchi of Aristotle and are retained at the end of our manuals of logic. But if the order ofhistory were followed, they should be placed not at the end but at the beginning of them;for they belong to the age in which the human mind was first making the attempt todistinguish thought from sense, and to separate the universal from the particular orindividual. How to put together words or ideas, how to escape ambiguities in the meaningof terms or in the structure of propositions, how to resist the fixed impression of an 'eternalbeing' or 'perpetual flux, ' how to distinguish between words and things-these wereproblems not easy of solution in the infancy of philosophy. They presented the same kind ofdifficulty to the half-educated man which spelling or arithmetic do to the mind of a child. Itwas long before the new world of ideas which had been sought after with such passionateyearning was set in order and made ready for use. To us the fallacies which arise in the preSocratic philosophy are trivial and obsolete because we are no longer liable to fall into theerrors which are expressed by them. The intellectual world has become better assured tous, and we are less likely to be imposed upon by illusions of words.The logic of Aristotle is for the most part latent in the dialogues of Plato. The nature ofdefinition is explained not by rules but by examples in the Charmides, Lysis, Laches, Protagoras, Meno, Euthyphro, Theaetetus, Gorgias, Republic; the nature of division islikewise illustrated by examples in the Sophist and Statesman; a scheme of categories isfound in the Philebus; the true doctrine of contradiction is taught, and the fallacy of arguingin a circle is exposed in the Republic; the nature of synthesis and analysis is graphicallydescribed in the Phaedrus; the nature of words is analysed in the Cratylus; the form of thesyllogism is indicated in the genealogical trees of the Sophist and Statesman; a truedoctrine of predication and an analysis of the sentence are given in the Sophist; thedifferent meanings of one and being are worked out in the Parmenides. Here we have mostof the important elements of logic, not yet systematized or reduced to an art or science, butscattered up and down as they would naturally occur in ordinary discourse. They are oflittle or no use or significance to us; but because we have grown out of the need of them weshould not therefore despise them. They are still interesting and instructive for the lightwhich they shed on the history of the human min