INTRODUCTION TO THE THEAETETUS

In the Theaetetus Eucleides the Megarian repeats to his friend Terpsion a conversation between Socrates, the mathematician Theodorus, and the youth Theaetetus, who was himself a mathematician of note. The subject is the nature of knowledge, and the discussion is interrupted and furthered by two digressions, one concerning midwives, in which Socrates likens his method of investigation to the activities of the midwife, the other contrasting the lawyer and the philosopher. 5-

The definition of knowledge is hard to attain, and is, in fact, not attained in this dialogue. The confusion between knowledge and various kinds or applications of knowledge is first cleared up, and then the discussion centres upon three definitions: (1) Knowledge is sensible perception; (2) Knowledge is true opinion; (3) Knowledge is true opinion with reasoned explanation.

The discussion of the first definition contains as one of its most important parts the refutation of the doctrine of Protagoras that "man is the measure of all things"; but it includes also a discussion of the doctrine of Heracleitus, that all things are always in