How is it then that no one feels Pleasure continuously? is it not that he wearies, because all human faculties are incapable of unintermitting exertion; and so, of course, Pleasure does not arise either, because that follows upon the act of Working. But there are some things which please when new, but afterwards not in the like way, for exactly the same reason: that at first the mind is roused and works on these Objects with its powers at full tension; just as they who are gazing stedfastly at anything; but afterwards the act of Working is not of the kind it was at first, but careless, and so the Pleasure too is dulled.
Again, a person may conclude that all men grasp at Pleasure, because all aim likewise at Life and Life is an act of Working, and every man works at and with those things which also he best likes; the musical man, for instance, works with his hearing at music; the studious man with his intellect at speculative questions, and so forth. And Pleasure perfects the acts of Working, and so Life after which men grasp. No wonder then that they aim also at Pleasure, because to each it perfects Life, which is itself choice-worthy. (We will take leave to omit the question whether we choose Life for Pleasure’s sake of Pleasure for Life’s sake; because these two plainly are closely connected and admit not of separation; since Pleasure comes not into being without Working, and again, every Working Pleasure perfects.)
And this is one reason why Pleasures are thought to differ in kind, because we suppose that things which differ in kind must be perfected by things so differing: it plainly being the case with the productions of Nature and Art; as animals, and trees, and pictures, and statues, and houses, and furniture; and so we suppose that in like manner acts of Working which are different in kind are perfected by things differing in kind. Now Intellectual Workings differ specifically from those of the Senses, and these last from one another; therefore so do the Pleasures which perfect them.