At the Plough and Stars in Cambridge, Massachusetts, I once heard an Irish banjo-player fly into a rage at someone’s refusal to stand him a ninth drink. ‘I play me music for nothin’,’ he explained. ‘And what do I get for it? Fock all!’ Maybe Michael Sandel, who teaches government at Harvard, just down the street, has met him. Sandel’s new book, What Money Can’t Buy, describes a confusion that is widespread even among policymakers and other putatively sober people: what should we do only out of love or duty, and what should we expect to get paid for?