Epstein sketches an amusing yet serious anatomy of friendship in its contemporary version: its duties and requirements (“Reciprocity, or Is It Obligation?â€), the various kinds of friendships (“A Little Taxonomy of Friendsâ€), the differences between male and female friendships, the complications marriage creates (“Friendship’s New Rivalâ€), even what happens when sex enters the equation. Moving easily from Aristotle to Seinfeld, and drawing on his own experiences with people great (Saul Bellow and Ralph Ellison) and unknown (an army bunkmate), he uncovers the rich and often surprising truths of friendship, illuminating those relationships -- contradictory, complicated, and wonderful -- without which we'd all be lost.