Plato on Sense-Perception and Knowled ge (Theaetetus 184-186)

Plato's argument in the Theaetetus (184 b 186 e) against the proposal that knowledge be defined as caatqaL1 has, I think, not yet been fully understood or rightly appreciated. Existing interpretations fall into two groups. On the one hand, F. M. Cornford2 and others think that Plato rejects the proposal on the ground that the objects which we perceive are not the sort of objects of which one could have knowledge: only the unchanging Forms can be known. On the other hand, there are those3 who think Plato's argument has nothing to do with Forms but instead turns on a distinction between sensation and judgment which has the consequence that the thinking we do about the deliverances of the senses, and not the mere use of the senses, is the source of our knowledge. The interpretation which I advance in this paper belongs to the second of these two broad classes, but differs from others in providing a more careful account of the distinctions which Plato seems to be making in this passage. Much of the interest of the argument lies, I think, in the analysis of the process of perception which Plato produces by distinguishing carefully the contribution of the senses from that of the mind; but this analysis has not been given the attention it deserves. The complexities of the argument can be usefully indicated by a brief examination of Comford's interpretation. According to Cornford Plato's argument proceeds in two stages. In the first (184 b 186 a 1) Plato concludes that there is knowledge which is not a matter of per-