"Socrates
"Please assume, then, for the sake of argument, that there is in our souls a block of wax, in one case larger, in another smaller, in one case the wax is purer, in another more impure and harder, in some cases softer.
"Theaetetus
"I assume all that.
"Socrates
"Let us, then, say that this is the gift of Memory, the mother of the Muses, and that whenever we wish to remember anything we see or hear or think of in our own minds, we hold this wax under the perceptions and thoughts and imprint them upon it, just as we make impressions from seal rings; and whatever is imprinted we remember and know as long as its image lasts, but whatever is rubbed out or [191e] cannot be imprinted we forget and do not know.
"Theaetetus
"Let us assume that.
"Socrates
"Now take a man who knows the things which he sees and hears, and is considering some one of them; observe whether he may not gain a false opinion in the following manner. Theaetetus In what manner? Socrates By thinking that the things which he knows are sometimes things which he knows and sometimes things which he does not know. For we were wrong before in agreeing that this is impossible.
"Theaetetus
"What do you say about it now?" (Plato, Theaetetus, 191c-e)
Plato's complete discussion in the Theaetetus of false judgment as the inappropriate linkage of a perception to a memory – the mind as a wax tablet– appears in lines 191a–196c of the dialogue.