"Mill's empiricism inclined him to think that only something experienced can be valuable as an end. He agreed with Bentham that our direct encounter with value occurs in the experience of pleasure. Delight or felt satisfaction was, according to his official view, the only thing desirable for its own sake; everything else was to be sought solely as means to this end. He made it perfectly clear that he meant by pleasure a state of feeling which, though it may be indefinable, is nevertheless well known and easily recognised by us.
Perhaps it was the evident identification, in ordinary language and thought, of feeling happy with being pleased that occasioned Mill to say that happiness is simply pleasure and the absence of pain. However this may be, the identification had the powerful effect of enlisting the acknowledged and supposedly universal search for happiness as evidence for the truth of hedonism. Bentham adopted the bold view that hedonism was correct both in its psychological and in its ethical forms, viz. that pleasure was both the only object of human choice and the only worthy object. But Mill's generous sympathies and deeper insight into human nature did not let him rest with such a dogmatic and impoverished doctrine. He respected variety in motivations too much to believe that they could all be reduced to a single, simple one."
Utilitarianism On The Net