SOCRATES: Consider a further point: did we not understand them to explain the generation of heat, whiteness, or anything else, in some such manner as the following:—were they not saying that each of them is moving between the agent and the patient, together with a perception, and that the patient ceases to be a perceiving power and becomes a percipient, and the agent a quale instead of a quality? I suspect that quality may appear a strange and uncouth term to you, and that you do not understand the abstract expression. Then I will take concrete instances: I mean to say that the producing power or agent becomes neither heat nor whiteness but hot and white, and the like of other things. For I must repeat what I said before, that neither the agent nor patient have any absolute existence, but when they come together and generate sensations and their objects, the one becomes a thing of a certain quality, and the other a percipient. You remember?
THEODORUS: Of course.
SOCRATES: We may leave the details of their theory unexamined, but we must not forget to ask them the only question with which we are concerned: Are all things in motion and flux?
THEODORUS: Yes, they will reply.
SOCRATES: And they are moved in both those ways which we distinguished, that is to say, they move in place and are also changed?
THEODORUS: Of course, if the motion is to be perfect.
SOCRATES: If they only moved in place and were not changed, we should be able to say what is the nature of the things which are in motion and flux?
THEODORUS: Exactly.
SOCRATES: But now, since not even white continues to flow white, and whiteness itself is a flux or change which is passing into another colour, and is never to be caught standing still, can the name of any colour be rightly used at all?
THEODORUS: How is that possible, Socrates, either in the case of this or of any other quality—if while we are using the word the object is escaping in the flux?