SOC. And will you also be ready to agree that it is impossible to perceive through one sense

 
what you perceive through another; for instance, to perceive through sight what you perceive through hearing, or through hearing what you perceive through sight? THEAET. Of course I shall. SOC. Then if you have any thought about both of these together, you would not have perception about both together either through one organ or through the other. THEAET. No. SOC. Now in regard to sound and color, you have, in the first place, this thought about both of them, that they both exist? THEAET. Certainly. SOC. And that each is different from the other and the same as itself? THEAET. Of course. SOC. And that both together are two and each separately is one? THEAET. Yes, that also. SOC. And are you able also to observe whether they are like or unlike each other? THEAET. May be. SOC. Now through what organ do you think all this about them? For it is impossible to grasp that which is common to them both either through hearing or through sight. Here is further evidence for the point I am trying to make: if it were possible to investigate the question whether the two, sound and color, are bitter or not, you know that you will be able to tell by what faculty you will investigate it, and that is clearly
 
neither hearing nor sight, but something else. THEAET. Of course it is,—the faculty exerted through the tongue. SOC. Very good. But through what organ is the faculty exerted which makes known to you that which is common to all things, as well as to these of which we are speaking—that which you call being and not-being, and the other attributes of things, about which we were asking just now? What organs will you assign for all these, through which that part of us which perceives gains perception of each and all of them? THEAET. You mean being and not-being, and likeness and unlikeness, and identity and difference,
 
and also unity and plurality as applied to them. And you are evidently asking also through what bodily organs we perceive by our soul the odd and the even and everything else that is in the same category. SOC. Bravo, Theaetetus! you follow me exactly; that is just what I mean by my question. THEAET. By Zeus, Socrates, I cannot answer, except that I think there is no special organ at all for these notions, as there are for those others; but it appears to me that the soul views by itself directly
 
what all things have in common. SOC. Why, you are beautiful, Theaetetus, and not, as Theodorus said, ugly; for he who speaks beautifully is beautiful and good. But besides being beautiful, you have done me a favor by relieving me from a long discussion, if you think that the soul views some things by itself directly and others through the bodily faculties; for that was my own opinion, and I wanted you to agree.