Aristotle, Eudemian Ethics

It is clear from this that the primary friendship, that of the good, is mutual reciprocity of affection and purpose. For the object of affection is dear to the giver of it, but also the giver of affection is himself dear to the object. This friendship, therefore, only occurs in man, for he alone perceives purpose; but the other forms occur also in the lower animals. Indeed mutual utility manifestly exists to some small extent between the domestic animals and man, and between animals themselves, for instance Herodotus's account of the friendship between the crocodile and the sandpiper,¹ and the perching together and separating of birds of which soothsayers speak. The bad may be each other's friends from motives both of utility and of pleasure; though some say that they are not really friends, because the primary kind of friendship does not belong to them, since obviously a bad man will injure a bad man, and those who suffer injury from one another do not feel affection for one another. But as a matter of fact bad men do feel affection for one another, though not according to the primary form of friendship—because clearly nothing hinders their being friends under the other forms, since for the sake of pleasure they put up with one another although they are being harmed, so long as they are lacking in self-restraint. The view is also held, when people look into the matter closely, that those who feel affection for each other on account of pleasure are not friends, because it is not the primary friendship, since that is reliable but this is unreliable. [20] But as a matter of fact it is friendship, as has been said, though not that sort of friendship but one derived from it. Therefore to confine the use of the term friend to that form of friendship alone is to do violence to observed facts, and compels one to talk paradoxes; though it is not possible to bring all friendship under one definition. The only remaining alternative, therefore, is, that in a sense the primary sort of friendship alone is friendship, but in a sense all sorts are, not as having a common name by accident and standing in a merely chance relationship to one another, nor yet as falling under one species, but rather as related to one thing.

And since the same thing is absolutely good and absolutely pleasant at the same time if nothing interferes, and the true friend and friend absolutely is the primary friend, and such is a friend chosen in and for himself (and he must necessarily be such, for he for whom one wishes good for his own sake must necessarily be desirable for his own sake), a true friend is also absolutely pleasant; owing to which it is thought that a friend of any sort is pleasant. But we must define this still further, for it is debatable whether what is good merely for oneself is dear or what is absolutely good, and whether the actual exercise of affection is accompanied by pleasure, so that an object of affection is also pleasant, or not. Both questions must be brought to the same issue; for things not absolutely good but possibly evil are to be avoided, and also a thing not good for oneself is no concern of oneself, but what is sought for is that things absolutely good shall be good for oneself. For the absolutely good is absolutely desirable, but what is good for oneself is desirable for oneself;