Ignored by modern philosophy, maligned by the Enlightenment, friendship hasn’t had a champion since the Greeks

The Enlightenment instantiated a wide-ranging cultural revolution that reshaped western identity. It is the crucible from which modern western societies emerged, and our mental architecture continues to employ the categories, language and concepts of its thought. As the Italian scholar Vincenzo Ferrone memorably put it, the Enlightenment is the “laboratory of modernity.” So while it might take some effort to imaginatively enter, say, the world of Socrates, Aristotle or Augustine, it is relatively easy for us to think ourselves into an 18th-century mindset. And this is for the straightforward reason that the complexity of ideas, institutions and practices that so exercised the philosophers of Paris, the learned societies of Edinburgh or the delegates to the Continental Congress in Philadelphia continue to animate and inform our own world.

It is from the 18th century that we have inherited a Kantian morality of...