Generally, friendship exists for three reasons: a) virtue b) usefulness c) pleasure. When virtue is the reason, friendship exists for the sake of friendship; where both like each other and cherish each other for some creditable values in the other’s personality. You wish to be the friend of that person for the sheer personality that he/she has. It has a magic in itself. It attracts you. And it is mutual. You know that you would even die to swear your friendship for that person. But you also know that the other would make you live than die for him/her. It is somewhat platonic in concept inasmuch as the other may not be/ need not be all that intelligent and good looking, useful or capable of giving pleasure.