SOC. Well, then, do you think that anyone ever considered in his own mind five and seven,—

 
I do not mean by setting before his eyes seven men and five men and considering them, or anything of that sort, but seven and five in the abstract, which we say are imprints in the block of wax, and in regard to which we deny the possibility of forming false opinions—taking these by themselves, do you imagine that anybody in the world has ever considered them, talking to himself and asking himself what their sum is, and that one person has said and thought eleven, and another twelve, or do all say and think that it is twelve? THEAET. No, by Zeus; many say eleven,
 
and if you take a larger number for consideration, there is greater likelihood of error. For I suppose you are speaking of any number rather than of these only. SOC. You are right in supposing so; and consider whether in that instance the abstract twelve in the block of wax is not itself imagined to be eleven. THEAET. It seems so. SOC. Have we not, then, come back again to the beginning of our talk? For the man who is affected in this way imagines that one thing which he knows is another thing which he knows. This we said was impossible, and
 
by this very argument we were forcing false opinion out of existence, that the same man might not be forced to know and not know the same things at the same time. THEAET. Very true. SOC. Then we must show that forming false opinion is something or other different from the interchange of thought and perception. For if it were that, we should never be deceived in abstract thoughts. But as the case now stands, either there is no false opinion or it is possible for a man not to know that which he knows. Which alternative will you choose? THEAET. There is no possible choice, Socrates. SOC. And yet the argument is not likely to admit both. But still, since we must not shrink from any risk, what if we should try to do a shameless deed? THEAET. What is it? SOC. To undertake to tell what it really is to know. THEAET. And why is that shameless? SOC. You seem not to remember that our whole talk from the beginning has been a search for knowledge, because we did not know what it is. THEAET. Oh yes, I remember. SOC. Then is it not shameless to proclaim what it is to know, when we are ignorant of knowledge? 
 
But really, Theaetetus, our talk has been badly tainted with unclearness all along; for we have said over and over again we know and we do not know and we have knowledge and we have no knowledge, as if we could understand each other, while we were still ignorant of knowledge; and at this very moment, if you please, we have again used the terms be ignorant and understand, as though we had any right to use them if we are deprived of knowledge. THEAET. But how will you converse, Socrates, if you refrain from these words?