SOCRATES: Then to think falsely is different from thinking that which is not?
THEAETETUS: It would seem so.
SOCRATES: Then false opinion has no existence in us, either in the sphere of being or of knowledge?
THEAETETUS: Certainly not.
SOCRATES: But may not the following be the description of what we express by this name?
THEAETETUS: What?
SOCRATES: May we not suppose that false opinion or thought is a sort of heterodoxy; a person may make an exchange in his mind, and say that one real object is another real object. For thus he always thinks that which is, but he puts one thing in place of another; and missing the aim of his thoughts, he may be truly said to have false opinion.
THEAETETUS: Now you appear to me to have spoken the exact truth: when a man puts the base in the place of the noble, or the noble in the place of the base, then he has truly false opinion.
SOCRATES: I see, Theaetetus, that your fear has disappeared, and that you are beginning to despise me.
THEAETETUS: What makes you say so?