Aristotle, Nicomachean Ethics
H. Rackham, Ed.

But things that are akin to things of different kinds must themselves differ in kind. [3] A still clearer proof may be drawn from the hindrance that activities receive from the pleasure derived from other activities. For instance, persons fond of the flute cannot give their attention to a philosophical discussion when they overhear someone playing the flute, because they enjoy music more than the activity in which they are engaged; therefore the pleasure afforded by the music of the flute impairs the activity of study. [4] The same thing occurs in other cases when a man tries to do two things at once; the pleasanter activity drives out the other, the more so if it is much more pleasant, until the other activity ceases altogether. Hence, when we enjoy something very much, we can hardly do anything else; and when we find a thing only mildly agreeable, we turn to some other occupation; for instance, people who eat sweets at the theater do so especially when the acting is bad. [5] And since our activities are sharpened, prolonged and improved by their own pleasure, and impaired by the pleasures of other activities, it is clear that pleasures differ widely from each other. In fact alien pleasures have almost the same effect on the activities as their own pains¹; since, when an activity causes pain, this pain destroys it, for instance, if a person finds writing or doing sums unpleasant and irksome; for he stops writing or doing sums, because the activity is painful. Activities then are affected in opposite ways by the pleasures and the pains that belong to them, that is to say, those that are intrinsically due to their exercise. Alien pleasures, as has been said, have very much the same effect as pain, for they destroy an activity, only not to the same degree. [6]

Again, since activities differ in moral value, and some are to be adopted, others to be avoided, and others again are neutral, the same is true also of their pleasures: for each activity has a pleasure of its own. Thus the pleasure of a good activity is morally good, that of a bad one morally bad; for even desires for noble things are praised and desires for base things blamed; but the pleasures contained in our activities are more intimately connected with them than the appetites which prompt them, for the appetite is both separate in time and distinct in its nature from the activity, whereas the pleasure is closely linked to the activity, indeed so inseparable from it as to raise a doubt whether the activity is not the same thing as the pleasure. [7] However, we must not regard pleasure as really being a thought or a sensation—indeed this is absurd, though because they are inseparable they seem to some people to be the same.

As then activities are diverse, so also are their pleasures.