ABSTRACT
Most modern men take it for granted that empirical knowledge is dependent upon, or derived from, perception. There is however in Plato and among philosophers of certain other schools a very different doctrine, to the effect that there is nothing worthy to be called 'knowledge' to be derived from the senses, and the only real knowledge has to do with concepts. This chapter deals with Plato's criticism of the view that knowledge is the same thing as perception, which occupies the first half of the Theaetetus. The idea of a relational proposition seems to have puzzled Plato, as it did most of the great philosophers down to Hegel. The doctrine of universal flux is caricatured by Plato, and it is difficult to suppose that any one ever held it in the extreme form that he gives to it. It seems that neither Plato nor the dynamic youths of Ephesus had noticed that locomotion is impossible on the extreme Heraclitean doctrine.
