STRANGER: You mean to say that false opinion thinks what is not?
THEAETETUS: Of course.
STRANGER: Does false opinion think that things which are not are not, or that in a certain sense they are?
THEAETETUS: Things that are not must be imagined to exist in a certain sense, if any degree of falsehood is to be possible.
STRANGER: And does not false opinion also think that things which most certainly exist do not exist at all?
THEAETETUS: Yes.
STRANGER: And here, again, is falsehood?
THEAETETUS: Falsehood—yes.
STRANGER: And in like manner, a false proposition will be deemed to be one which asserts the non-existence of things which are, and the existence of things which are not.
THEAETETUS: There is no other way in which a false proposition can arise.