Friends are a constant feature of our lives, yet friendship itself is difficult to define. Even Michel de Montaigne, author of the seminal essay "Of Friendship," found it nearly impossible to account for the great friendship of his life. Why is something so commonplace and universal so hard to grasp? What is it about the nature of friendship that proves so elusive?

In On Friendship, the acclaimed philosopher Alexander Nehamas launches an original and far-ranging investigation of friendship. Exploring the long history of philosophical thinking on the subject, from Aristotle to Emerson and beyond, and drawing on examples from literature, art, drama, and his own life, Nehamas shows that for centuries, friendship was as much a public relationship as it was a private one-inseparable from politics and commerce, favors and perks. Now that it is more firmly in the private realm, Nehamas holds, close friendship is central to the good life.

Profound and affecting, On Friendship sheds light on why we love our friends-and how they determine who we are, and who we might become.