Book 10: Pleasure.
Eudoxus thought pleasure was the good, because he saw that all beings, both rational and irrational, strive after it; but in all cases, he said, that which is desirable is the good, and that which is most desirable is best: the fact, then, that all beings incline to one and the same thing indicates that this is the best thing for all (for each being finds out what is good for itself—its food, for instance); but that which is good for all, and which all strive after, is the good.
The statements of Eudoxus were accepted rather because of the excellence of his character than on their own account; for he seemed to be a remarkably temperate man; and so people thought that it was not from love of pleasure that he spoke thus, but that what he said really was the fact.
Eudoxus also thought that his point could be proved no less clearly by the argument from the opposite of pleasure:—pain is, in itself, an object of aversion to all beings; therefore its opposite is desirable for all.
Again, he argued, that is most desirable which we choose, not on account of something else, but for its own sake: but this is admitted to be the case with pleasure; for we never ask a man for his motive in taking pleasure, it being understood that pleasure is in itself desirable.
Again, he argued that any good thing whatsoever is made more desirable by the addition of pleasure, e.g. just or temperate conduct; but it can only be by the good that the good is increased.
Now, this last argument seems indeed to show that pleasure is a good thing, but not that it is one whit better than any other good thing; for anygood thing is more desirable with the addition of another good thing than by itself.
Nay, Plato actually employs a similar argument to show that pleasure is not the good. “The pleasant life,” he says, “is more desirable with wisdom than without: but if the combination of the two be better, pleasure itself cannot be the good; for no addition can make the good more desirable.” And it is equally evident that, if any other thing be made more desirable by the addition of one of the class of things that are good in themselves, that thing cannot be the good. What good is there, then, which is thus incapable of addition, and at the same time such that men can participate in it? For that is the sort of good that we want.
But those who maintain, on the contrary, that what all desire is not good, surely talk nonsense. What all men think, that, we say, is true. And to him who bids us put no trust in the opinion of mankind, we reply that we can scarce put greater trust in his opinion. If it were merely irrational creatures that desired these things, there might be something in what he says; but as rational beings also desire them, how can it be anything but nonsense? Indeed, it may be that even in inferior beings there is some natural principle of good stronger than themselves, which strives after their proper good.
Again, what the adversaries of Eudoxus say about his argument from the nature of the opposite of pleasure, does not seem to be sound. They say that, though pain be bad, yet it does not follow that pleasure is good; for one bad thing may be opposed to another bad thing, and both to a third thing which is different from either. Now, though this is not a bad remark, it does not hold true in the present instance. For if both were bad, both alike ought to be shunned, or if neither were bad, neither should be shunned, or, at least, one no more than the other: but, as it is, men evidently shun the one as bad and choose the other as good; they are, in fact, therefore, opposed to one another in this respect.