There are no rules for friendship. It must be left to itself. We cannot force it any more than love.

Instead of loving your enemies - treat your friends a little better.

Be slow to fall into friendship but when thou art in, continue firm and constant.

One's friends are that part of the human race with which one can be human.

The greatest gift of life is friendship, and I have received it.

Friends... they cherish one another's hopes. They are kind to one another's dreams.

Friendship is a plant of slow growth and must undergo and withstand the shocks of adversity before it is entitled to the appellation.

Am I not destroying my enemies when I make friends of them?

Friendship is unnecessary, like philosophy, like art... It has no survival value rather it is one of those things that give value to survival.