STRANGER: What then shall we call it?
THEAETETUS: Clearly, not-being; and this is the very nature for which the Sophist compelled us to search.
STRANGER: And has not this, as you were saying, as real an existence as any other class? May I not say with confidence that not-being has an assured existence, and a nature of its own? Just as the great was found to be great and the beautiful beautiful, and the not-great not-great, and the not-beautiful not-beautiful, in the same manner not-being has been found to be and is not-being, and is to be reckoned one among the many classes of being. Do you, Theaetetus, still feel any doubt of this?
THEAETETUS: None whatever.
STRANGER: Do you observe that our scepticism has carried us beyond the range of Parmenides' prohibition?
THEAETETUS: In what?
STRANGER: We have advanced to a further point, and shown him more than he forbad us to investigate.
THEAETETUS: How is that?
STRANGER: Why, because he says—
'Not-being never is, and do thou keep thy thoughts from this way of enquiry.'