Aristotle, Nicomachean Ethics
H. Rackham, Ed.

and this is especially strong in the human race; for which reason we praise those who love their fellow men.¹ Even when travelling abroad one can observe that a natural affinity and friendship exist between man and man universally. 1. [4] Moreover, as friendship appears to be the bond of the state; and lawgivers seem to set more store by it than they do by justice, for to promote concord, which seems akin to friendship, is their chief aim, while faction, which is enmity, is what they are most anxious to banish. And if men are friends, there is no need of justice between them; whereas merely to be just is not enough—a feeling of friendship also is necessary. Indeed the highest form of justice seems to have an element of friendly feeling in it.² 1. [5]

And friendship is not only indispensable as a means, it is also noble in itself. We praise those who love their friends, and it is counted a noble thing to have many friends; and some people think that a true friend must be a good man. 1. [6]

But there is much difference of opinion as to the nature of friendship. Some define it as a matter of similarity; they say that we love those who are like ourselves: whence the proverbs ‘Like finds his like,’ ‘Birds of a feather flock together,’³ and so on. Others on the contrary say that with men who are alike it is always a case of ‘two of a trade.’⁴