Aristotle, Nicomachean Ethics
H. Rackham, Ed.

[5] Again, these thinkers' refutation of the argument from the converse appears equally unsound. They pain say, if pain is bad, it does not follow therefore that pleasure is good: for an evil can also be opposed to an evil and to a thing that is neither good nor evil: a statement which is indeed sound enough, but which does not apply to the things in question. If both pleasure and pain were in the class of evils, both would be also of necessity things to be avoided, and if in the class of things neutral, neither ought to be avoided, or they ought to be avoided alike; but as it is we see men avoid pain as evil and choose pleasure as good; it is therefore as good and evil that they are opposed.