Aristotle, Nicomachean Ethics
H. Rackham, Ed.

Endymion. But for a living being, if we eliminate action, and a fortiori creative action, what remains save contemplation? It follows that the activity of God, which is transcendent in blessedness, is the activity of contemplation; and therefore among human activities that which is most akin to the divine activity of contemplation will be the greatest source of happiness. [8]

A further confirmation is that the lower animals cannot partake of happiness, because they are completely devoid of the contemplative activity. The whole of the life of the gods is blessed, and that of man is so in so far as it contains some likeness to the divine activity; but none of the other animals possess happiness, because they are entirely incapable of contemplation. Happiness therefore is co-extensive in its range with contemplation: the more a class of beings possesses the faculty of contemplation, the more it enjoys happiness, not as an accidental concomitant of contemplation but as inherent in it, since contemplation is valuable in itself. It follows that happiness is some form of contemplation. [9]

But the philosopher being a man will also need external well—being, since man's nature is not self—sufficient for the activity of contemplation, but he must also have bodily health and a supply of food and other requirements.