SOCRATES: The reason why I am thus precise is, because I want to know whether, when we perceive black and white through the eyes, and again, other qualities through other organs, we do not perceive them with one and the same part of ourselves, and, if you were asked, you might refer all such perceptions to the body. Perhaps, however, I had better allow you to answer for yourself and not interfere. Tell me, then, are not the organs through which you perceive warm and hard and light and sweet, organs of the body?
THEAETETUS: Of the body, certainly.
SOCRATES: And you would admit that what you perceive through one faculty you cannot perceive through another; the objects of hearing, for example, cannot be perceived through sight, or the objects of sight through hearing?
THEAETETUS: Of course not.
SOCRATES: If you have any thought about both of them, this common perception cannot come to you, either through the one or the other organ?
THEAETETUS: It cannot.
SOCRATES: How about sounds and colours: in the first place you would admit that they both exist?
THEAETETUS: Yes.
SOCRATES: And that either of them is different from the other, and the same with itself?
THEAETETUS: Certainly.