Then is it not already clear that neither of these two contained the good for if it did contain the good, it would be sufficient and perfect, and such as to be chosen by all living creatures which would be able to live thus all their lives; and if any of us chose anything else, he would be choosing contrary to the nature of the truly desirable, not of his own free will, but from ignorance or some unfortunate necessity.
In fact, a similar argument is employed by Plato to refute the view that pleasure is the Good: the life of pleasure, he urges, is more desirable in combination with intelligence than without it; but if pleasure combined with something else is better than pleasure alone, it is not the Good, for the Good is not rendered more desirable by the addition of anything to it. And it is clear that nothing else either will be the Good if it becomes more desirable when combined with something good in itself. What thing is there then of this nature, which is attainable by us? for it is something of this nature that we are in search of.
The Philebus tests a life of pleasure without thought and a life of thought without pleasure, and finds neither sufficient or choiceworthy on its own, so neither is the good. Aristotle names Plato, states the argument as a rule (whatever improves when something is added is not the good) and turns it against Eudoxus' hedonism. He then asks for a good that passes the test and is within our reach, the criterion of completeness and self-sufficiency that Book I already applies to happiness.
