EPISTEMOLOGY momentary items, twins begotten together by the encounter of the parent eye and the parent marble (156c–d) If, then, on a particular occasion I say ‘This is white’, I cannot be wrong: no one else is in a position to contradict me The same is true of other kinds of sense-perception (157a) Let us suppose we concede to Protagoras that, in such a case, what the perceiver says goes Still, Socrates insists, there are many other kinds of case where it would be absurd to make such a claim We have dreams in which we think we are Xying; a man may go mad and think he is a god Surely these are cases where what seems to a person is not true? And even the ordinary cases, where the perception is not erroneous, cannot be cases of real knowledge For how can we be sure that we are not dreaming? Half our life is spent abed, and it is a commonplace that it is impossible to prove that one is awake and not asleep (158c–e) At this point Socrates oVers Theaetetus (and Protagoras) a response— rather a feeble response, since it deals with the case not of dreamers or madmen, but of sick people whose senses are aVected by their disease Suppose Socrates falls ill, and sweet wine begins to taste sour to him On the Heraclitean account, the taste of the wine is the oVspring of the wine and the taster Socrates sick is a diVerent taster from Socrates healthy, and with a diVerent parent naturally the oVspring diVers It may not be true that the wine is sour, but it is, in his sickness, sour for Socrates So we not have here a case of erroneous perception, and the equivalence of knowledge and perception is not yet defeated Socrates in the dialogue moves on to diVerent terrain There are cases of perception without knowledge: we can hear a foreign language spoken, and yet not know the language (163b) There are cases of knowledge without perception: when we shut our eyes and recall something we have seen, we know what it looks like and yet are no longer seeing it (164a) But if knowing ¼ perception, then both these must be cases of simultaneously knowing and not knowing, and surely that is an absurdity? But even now, Socrates is willing to allow Protagoras a way out It is easy to have cases of simultaneous perception and non-perception: if you wear an eyepatch you see something with one eye but not with the other So if perception ¼ knowledge, it is no surprise that you can both know and not know at the same time (165c) In discussing Theaetetus’ identiWcation of knowledge and perception, Plato’s Socrates gives Protagoras a surprising amount of rope But he is, in 153