So long, then, as both the object of thought or of sense and the perceptive or contemplative subject are as they ought to be, so long will there be pleasure in the exercise; for so long as the object to be acted upon and the subject that is able to act remain the same, and maintain the same relation to each other, the result must be the same.

How is it, then, that we are incapable of continuous pleasure? Perhaps the reason is that we become exhausted; for no human faculty is capable of continuous exercise. Pleasure, then, also cannot be continuous; for it is an accompaniment of the exercise of faculty. And for the same reason some things please us when new, but afterwards please us less. For at first the intellect is stimulated and exercises itself upon them strenuously, just as we strain our eyes to look hard at something; but after a time the exertion ceases to be so intense, and becomes relaxed; and so the pleasure also loses its keenness.

The desire for pleasure we should expect to be shared by all men, seeing that all desire to live.