Aristotle in the Book Magna Moralia, Cap XIII, about friendship, explains what he understands as friendship: "In our opinion, there is only true friendship where there is reciprocity of affection. But friendship, love for God, has no reciprocity, and friendship is impossible, nor can there be reciprocity of friendship with inanimate things ... Therefore the friendship or the love for God is not the object of our study .... "
All the analyzes of Aristotle must be made from this point, because Aristotle does not study the spirit but the human soul.
In Eudemian Ethics, Book VII, he affirms: "It is also said about friendship affirmations as: " friendship is equality "," true friends have only one soul". All these statements are refer to the individual, because this is the way as the individual wishes the good to himself ... And to desire, mainly, the coexistence, to live together, to share the joy and the pain and to be, therefore, a single soul, and not to be able to live the one without the other, but wish to die together."
Aristotle is talking about the individual as a friend, not only as a friend of others but as a friend of himself, of the soul as a unit. When the soul is multiple and struggles against itself (because of the effect of the passions for example) man can be an enemy of himself.
One soul, one heart. Speaking of one soul is talk of concord, the union of hearts, the union of wills. In true friendship man is a friend of himself and of the neighbor. In true friendship men are not together for pleasure or to find some benefit but for the search of the good. The good unite men in true friendship, is for that we can say that in anothe way that true friends have one soul.
Good and evil give rise to different forms of friendship. In the perverts we can not talk about the same because the perverted man is not one but multiple. In falsehood as the desire are opposed the disputes arise. We share with our neighbor our essence, our soul only in the dimension of the good and the true.