Aristotle, Eudemian Ethics

[1238a] [1] For a friend is not to be had without trial and is not a matter of a single day, but time is needed; hence the peck of salt' has come to be proverbial. At the same time if a friend is really to be your friend he must be not only good absolutely but also good to you; for a man is good absolutely by being good, but he is a friend by being good to another, and he is both good absolutely and a friend when both these attributes harmonize together, so that what is good absolutely is also good for another person; or also he may be not good absolutely yet good to another because useful. But being a friend of many people at once is prevented even by the factor of affection, for it is not possible for affection to be active in relation to many at once.

These things, therefore, show the correctness of the saying that friendship is a thing to be relied on, just as happiness is a thing that is self-sufficing. And it has been rightly said¹: "Nature is permanent, but wealth is not—" although it would be much finer to say 'Friendship' than 'Nature.'² And it is proverbial that time shows a friend, and also misfortunes more than good fortune. For then the truth of the saying 'friends' possessions are common property' is clear for only friends, instead of the natural goods and natural evils on which good and bad fortune turn, choose a human being rather than the presence of the former and the absence of the latter; [20] and misfortune shows those who are not friends really but only because of some casual utility. And both are shown by time; for even the useful friend is not shown quickly, but rather the pleasant one—except that one who is absolutely pleasant is also not quick to show himself. For men are like wines and foods; the sweetness of those is quickly evident, but when lasting longer it is unpleasant and not sweet, and similarly in the case of men. For absolute pleasantness is a thing to be defined by the End it effects and the time it lasts. And even the multitude would agree, not in consequence of results only, but in the same way as in the case of a drink they call it sweeter—for a drink fails to be pleasant not because of its result, but because its pleasantness is not continuous, although at first it quite takes one in.

The primary form of friendship therefore, and the one that causes the name to be given to the others, is friendship based on goodness and due to the pleasure of goodness, as has been said before. The other friendships occur even among children and animals and wicked people: whence the sayings— "Two of an age each other gladden" and "Pleasure welds the bad man to the bad."³

And also the bad may be pleasant to each other not as being bad or neutral,⁴ but if for instance both are musicians or one fond of music and the other a musician, and in the way in which all men have some good in them and so fit in with one another. Further they might be mutually useful and beneficial (not absolutely but for their purpose) not as being bad or neutral.