Aristotle, Nicomachean Ethics
H. Rackham, Ed.

As then lovers find their greatest delight in seeing those they love, and prefer the gratification of the sense of sight to that of all the other senses, that sense being the chief seat and source of love, so likewise for friends （may we not say?） the society of each other is the most desirable thing there is. For （i） friendship is essentially a partnership. And （ii） a man stands in the same relation to a friend as to himself¹; but the consciousness of his own existence is a good; so also therefore is the consciousness of his friend's existence; but this² consciousness is actualized in intercourse; hence friends naturally desire each other's society. [2] And （iii） whatever pursuit it is that constitutes existence for a man or that makes his life worth living, he desires to share that pursuit with his friends. Hence some friends drink or dice together, others practise athletic sports and hunt, or study philosophy, in each other's company; each sort spending their time together in the occupation that they love best of everything in life; for wishing to live in their friends’ society, they pursue and take part with them in these occupations as best they can.³ [3]

Thus the friendship of inferior people is evil, for they take part together in inferior pursuits [being unstable,]⁴ and by becoming like each other are made positively evil. But the friendship of the good is good, and grows with their intercourse. And they seem actually to become better by putting their friendship into practice,⁵ and because they correct each other's faults, for each takes the impress from the other of those traits in him that give him pleasure—whence the saying: "Noble deeds from noble men."⁶

So much for our treatment of Friendship. Our next business will be to discuss Pleasure.