Theaetetus: What do you mean? Do not be afraid to speak.
Stranger: To that which is, may be attributed some other thing which is?
Theaetetus: Certainly.
Stranger: But can anything which is, be attributed to that which is not?
Theaetetus: Impossible.
Stranger: And all number is to be reckoned among things which are?
Theaetetus: Yes, surely number, if anything, has a real existence.
Stranger: Then we must not attempt to attribute to not-being number either in the singular or plural?
Theaetetus: The argument implies that we should be wrong in doing so.
Stranger: But how can a man either express in words or even conceive in thought things which are not or a thing which is not without number?
Theaetetus: How indeed?
Stranger: When we speak of things which are not, are we not attributing plurality to not-being?
Theaetetus: Certainly.
Stranger: But, on the other hand, when we say “what is not,” do we not attribute unity?
Theaetetus: Manifestly.
Stranger: Nevertheless, we maintain that you may not and ought not to attribute being to not-being?
Theaetetus: Most true.
Stranger: Do you see, then, that not-being in itself can neither be spoken, uttered, or thought, but that it is unthinkable, unutterable, unspeakable, indescribable?
Theaetetus: Quite true.
Stranger: But, if so, I was wrong in telling you just now that the difficulty which was coming is the greatest of all.
Theaetetus: What! is there a greater still behind?
Stranger: Well, I am surprised, after what has been said already, that you do not see the difficulty in which he who would refute the notion of not-being is involved. For he is compelled to contradict himself as soon as he makes the attempt.
Theaetetus: What do you mean? Speak more clearly.
Stranger: Do not expect clearness from me. For I, who maintain that not-being has no part either in the one or many, just now spoke and am still speaking of not-being as one; for I say “not-being.” Do you understand?
Theaetetus: Yes.