What happens when a dedicated life of the mind confronts the messiness of earthly desires? The Chicago University philosophy professor Agnes Callard, who in some moods believes herself to be channelling Socrates, was forced to ask herself that question one afternoon in 2011 when she was discussing with a graduate student a particular thorny problem in Greek thought, the abstract question of why one means something singularly different from two. In the course of unpacking this problem, another related dilemma arose, however: this was the insistent fact that the pair of them – student and teacher – had, in the...