Aristotle, Nicomachean Ethics
H. Rackham, Ed.

But granting （2） that some pleasures are bad, it does not therefore follow （3） that a certain pleasure may not nevertheless be the Supreme Good; just as a certain form of knowledge may be supremely good, although some forms of knowledge are bad. On the contrary （i） since every faculty has its unimpeded activity, the activity of all the faculties, or of one of them （whichever constitutes Happiness） , when unimpeded, must probably be the most desirable thing there is; but an unimpeded activity is a pleasure; so that on this showing the Supreme Good will be a particular kind of pleasure, even though most pleasures are bad, and, it may be, bad absolutely. This is why everybody thinks that the happy life must be a pleasant life, and regards pleasure as a necessary ingredient of happiness; and with good reason, since no impeded activity is perfect, whereas Happiness is essentially perfect; so that the happy man requires in addition the goods of the body, external goods and the gifts of fortune, in order that his activity may not be impeded through lack of them.