Nicomachean Ethics

​And there would also arise a certain training in virtue from living together with good people, just as Theognis also says. But to those who examine the matter more from the standpoint of nature, it seems that an excellent friend is naturally desirable for an excellent person. For what is good by nature has been said to be good and pleasant in itself for the excellent person. And they define living, in the case of animals, by the capacity for sensation, and in the case of humans, by sensation or thought. But capacity is referred back to activity, and what is primary lies in the activity. It seems indeed, then, that living is primarily sensing or thinking. And living is among the things that are good and pleasant in themselves; for it is determinate, and what is determinate belongs to the nature of the good; and what is good by nature is also good for the decent person; which is why it seems to be pleasant to all. But one must not take a wretched and corrupted life, nor one spent in pains; for such a life is indeterminate, just like its attributes. And in what follows concerning pain, this will be clearer. And if living itself is good and pleasant (as indeed seems to be the case from the fact that all desire it, and especially decent and blessed people; for to them life is most desirable, and their life is the most blessed), and the person who sees senses that he sees, and the person who hears that he hears, and the person who walks that he walks, and similarly in other cases there is something that senses that we are active, so that if we sense, we sense that we sense, and if we think, we sense that we think, and to sense that we sense or think is to sense that we exist (for to exist was defined as sensing or thinking); and to sense that one is alive is among the things that are pleasant in themselves (for life is good by nature, and to sense the good present in oneself is pleasant); and living is desirable, and especially for good people, because existence is good and pleasant for them (for by jointly sensing the good in itself, they are pleased); and as the excellent person is disposed toward himself, so he is also toward his friend (for the friend is another self); just as, therefore, one’s own existence is desirable for each person, so also is that of the friend, or nearly so. But existence was desirable because of one’s sensing of oneself as being good, and such sensing is pleasant in itself. One must, therefore, jointly sense also that the friend exists, and this would come about by living together and sharing in conversation and thought; for this is what “living together” would seem to mean in the case of humans, and not as with cattle, “feeding in the same place.” If, then, for the blessed person, existence is desirable in itself, being good and pleasant by nature, and that of the friend is very similar, then the friend would also be among the things that are desirable. But what is desirable for him, he must possess, or else he will be deficient in this respect. Therefore, the person who is to be happy will need excellent friends.