Soc. Thirst again is a destruction and a pain, but the filling with moisture
 of that which was dried up is a pleasure. Then, too, the unnatural dissolution and disintegration we experience through heat are a pain, but the natural restoration and cooling are a pleasure. Pro. Certainly. Soc. And the unnatural hardening of the moisture in an animal through cold is pain; but the natural course of the elements returning to their place and separating is a pleasure. See, in short, if you think it is a reasonable statement that whenever in the class of living beings,
 which, as I said before, arises out of the natural union of the infinite and the finite, that union is destroyed, the destruction is pain, and the passage and return of all things to their own nature is pleasure. Pro. Let us accept that; for it seems to me to be true in its general lines. Soc. Then we may assume this as one kind of pain and pleasure arising severally under the conditions I have described? Pro. Let that be assumed. Soc. Now assume within the soul itself the anticipation of these conditions,
 the sweet and cheering hope of pleasant things to come, the fearful and woful expectation of painful things to come. Pro. Yes, indeed, this is another kind of pleasure and pain, which belongs to the soul itself, apart from the body, and arises through expectation. Soc. You are right. I think that in these two kinds, both of which are, in my opinion, pure, and not formed by mixture of pain and pleasure, the truth about pleasure will be made manifest,
 whether the entire class is to be desired or such desirability is rather to be attributed to some other class among those we have mentioned, whereas pleasure and pain, like heat, cold, and other such things, are sometimes desirable and sometimes undesirable, because they are not good themselves, though some of them sometimes admit on occasion the nature of the good. Pro. You are quite right in saying that we must track our quarry on this trail. Soc. First, then, let us agree on this point: If it is true,
 as we said, that destruction is pain and restoration is pleasure, let us consider the case of living beings in which neither destruction nor restoration is going on, and what their state is under such conditions. Fix your mind on my question: Must not every living being under those conditions necessarily be devoid of any feeling of pain or pleasure, great or small? Pro. Yes, necessarily.