  The Theaetetus’ most important similarity to other Platonic dialogues is that it is aporetic—it is a dialogue that ends in an impasse. The Theaetetus reviews three definitions of knowledge in turn; plus, in a preliminary discussion, one would-be definition which, it is said, does not really count. Each of these proposals is rejected, and no alternative is explicitly offered. Thus we complete the dialogue without discovering what knowledge is. We discover only three things that knowledge is not (Theaetetus 210c; cp. 183a5, 187a1).