Aristotle, Nicomachean Ethics
H. Rackham, Ed.

4. The forms which friendly feeling for our neighbors takes, and the marks by which the different forms of friendship are defined, seem to be derived from the feelings of regard which we entertain for ourselves. A friend is defined as （a） one who wishes, and promotes by action, the real or apparent good of another for that other's sake; or （b） one who wishes the existence and preservation of his friend for the friend's sake. （This is the feeling of mothers towards their children, and of former friends who have quarrelled.¹） Others say that a friend is （c） one who frequents another's society, and （d） who desires the same things as he does, or （e） one who shares his friend's joys and sorrows. （This too is very characteristic of mothers.） Friendship also is defined by one or other of these marks.² [2] But each of them is also found in a good man's feelings towards himself （and in those of all other men as well, in so far as they believe themselves to be good; but, as has been said, virtue and the virtuous man seem to be the standard in everything）. [3] For （d） the good man is of one mind with himself, and desires the same things with every part of his nature. Also （a） he wishes his own good, real as well as apparent, and seeks it by action （for it is a mark of a good man to exert himself actively for the good） ; and he does so for his own sake （for he does it on account of the intellectual part of himself, and this appears to be a man's real self）. Also （b） he desires his own life and security, and especially that of his rational part. [4] For existence is good for the virtuous man; and everyone wishes his own good: no one would choose to possess every good in the world on condition of becoming somebody else （for God possesses the good even as it is）,³ but only while remaining himself, whatever he may be; and it would appear that the thinking part is the real self, or is so more than anything else. [5] And （c） the good man desires his own company; for he enjoys being by himself, since he has agreeable memories of the past, and good hopes for the future, which are pleasant too; also his mind is stored with subjects for contemplation. And （e） he is keenly conscious of his own joys and sorrows; for the same things give him pleasure or pain at all times, and not different things at different times, since he is not apt to change his mind.

It is therefore because the good man has these various feelings towards himself, and because he feels towards his friend in the same way as towards himself （for a friend is another self） , that friendship also is thought to consist in one or other of these feelings, and the possession of them is thought to be the test of a friend. [6]

Whether a man can be said actually to feel friendship for himself is a question that may be dismissed for the present; though it may be held that he can do so in so far⁴ as he is a dual or composite being,