Aristotle, Nicomachean Ethics
H. Rackham, Ed.

Also it is by rendering affection in proportion to desert that friends who are not equals may approach most nearly to true friendship, since this will make them equal. Amity consists in equality and similarity, especially the similarity of those who are alike in virtue; for being true to themselves, these also remain true to one another, and neither request nor render services that are morally degrading. Indeed they may be said actually to restrain each other from evil: since good men neither err themselves nor permit their friends to err. Bad men on the other hand have no constancy in friendship, for they do not even remain true to their own characters; but they can be friends for a short time, while they take pleasure in each other's wickedness. [6] The friendships of useful and pleasant people last longer, in fact as long as they give each other pleasure or benefit. It is friendship based on utility that seems most frequently to spring from opposites, for instance a friendship between a poor man and a rich one, or between an ignorant man and a learned; for a person desiring something which he happens to lack will give something else in return for it. One may bring under this class the friendship between a lover and the object of his affections, or between a plain person and a handsome one. This is why lovers sometimes appear ridiculous when they claim that their love should be equally reciprocated; no doubt if they are equally lovable this is a reasonable demand, but it is ridiculous if they have nothing attractive about them. [7]

But perhaps there is no real attraction between opposites as such, but only accidentally, and what they actually desire is the mean between them （since this is the Good）; the dry for instance striving not to become wet, but to reach an intermediate state, and so with the hot, and everything else. Let us however dismiss this question, as being indeed somewhat foreign to our subject. 9.

The objects and the personal relationships with which friendship is concerned appear, as was said at the outset,¹ to be the same as those which are the sphere of justice. For in every partnership we find mutual rights of some sort, and also friendly feeling: one notes that shipmates and fellow-soldiers speak of each other as ‘my friend,’ and so in fact do the partners in any joint undertaking. But their friendship is limited to the extent of their association in their common business, for so also are their mutual rights as associates. Again, the proverb says ‘Friends' goods are common property,’ and this is correct, since community is the essence of friendship. [2] Brothers have all things in common, and so do members of a comradeship²; other friends hold special possessions in common, more or fewer in different cases, inasmuch as friendships vary in degree. The claims of justice also differ in different relationships.