SOCRATES: When you speak of purity and clearness, or of excess, abundance, greatness and sufficiency, in what relation do these terms stand to truth?
PROTARCHUS: Why do you ask, Socrates?
SOCRATES: Because, Protarchus, I should wish to test pleasure and knowledge in every possible way, in order that if there be a pure and impure element in either of them, I may present the pure element for judgment, and then they will be more easily judged of by you and by me and by all of us.
PROTARCHUS: Most true.
SOCRATES: Let us investigate all the pure kinds; first selecting for consideration a single instance.
PROTARCHUS: What instance shall we select?
SOCRATES: Suppose that we first of all take whiteness.
PROTARCHUS: Very good.
SOCRATES: How can there be purity in whiteness, and what purity? Is that purest which is greatest or most in quantity, or that which is most unadulterated and freest from any admixture of other colours?
PROTARCHUS: Clearly that which is most unadulterated.