In the Theaetetus, after identifying Theaetetus' conjecture that knowledge is perception with Protagoras' theory that man is the measure of all things, Socrates associates this view with what he suggests may have been a ‘secret doctrine’ of Protagoras. What we say ‘is’ really is only in process of becoming: nothing is really of any definite sort. What is called white colour simply arises between the eye and the ‘motion’ which it encounters and is something peculiar to each several percipient. At this point (154b) Socrates goes on to say that ‘the thing which measures itself against the object or touches it’, like ‘the thing that we measure ourselves against’, is constantly undergoing change, for otherwise ‘when a different thing came into contact with it or were somehow modified, it, on its side, if it were not affected in itself, would not become different’. He continues, ‘For as things are we are too easily led into making statements which Protagoras and anyone who maintains the same position would call strange and absurd’, and he instances the case of six dice, which are said to be more when compared with four and fewer when compared with twelve, and himself, who is now taller than Theaetetus, but within a year will be shorter, without having lost in height (because Theaetetus is growing).