The word Sophist in modern languages means one who purposely uses fallacious arguments. Our definition was probably derived from that given by Aristotle in his _Topics_, but does not entirely reproduce it. What we call sophistry was with him eristic, or the art of unfair disputation; and by Sophist he means one who practises the eristic art for gain. He also defines sophistry as the appearance without the reality of wisdom. A very similar account of the Sophists and their art is given by Plato in what seems to be one of his later dialogues; and another dialogue, probably composed some time previously, shows us how eristic was actually practised by two Sophists, Euthydêmus and Dionysodôrus, who had learned the art, which is represented as a very easy accomplishment, when already old men. Their performance is not edifying; and one only wonders how any Greek could have been induced to pay for the privilege of witnessing such an exhibition. But the word Sophist, in its original signification, was an entirely honourable name. It meant a sage, a wise and learned man, like Solon, or, for that matter, like Plato and Aristotle themselves. The interval between these widely-different connotations is filled up and explained by a number of individuals as to whom our information is principally, though by no means entirely, derived from Plato. All of them were professional teachers, receiving payment for their services; all made a particular study of language, some aiming more particularly at accuracy, others at beauty of expression. While no common doctrine can be attributed to them as a class, as individuals they are connected by a series of graduated transitions, the final outcome of which will enable us to understand how, from a title of respect, their name could be turned into a byword of reproach. The Sophists, concerning whom some details have been transmitted to us, are Protagoras, Gorgias, Prodicus, Hippias, Pôlus, Thrasymachus, and the Eristics already mentioned. We have placed them, so far as their ages can be determined, in chronological order, but their logical order is somewhat different. The first two on the list were born about 480 B.C., and the second pair possibly twenty years later. But neither Protagoras nor Gorgias seems to have published his most characteristic theories until a rather advanced time of life, for they are nowhere alluded to by the Xenophontic Socrates, who, on the other hand, is well acquainted with both Prodicus and Hippias, while, conversely, Plato is most interested in the former pair. We shall also presently see that the scepticism of the elder Sophists can best be explained by reference to the more dogmatic theories of their younger contemporaries, which again easily fit on to the physical speculations of earlier thinkers.