Does illness have a meaning beyond itself? For most of history, people have thought so. It was a divine or other vengeance, a punishment for wickedness, individual or collective. The purely naturalistic attitude to illness is psychologically difficult to maintain consistently. Even the most thorough of rationalists, struck down unexpectedly by malady, are inclined to protest that they did not deserve it, and that they had no bad habits, exercised vigorously, and ate fresh food, for example.

In his 1931 novella Confidence Africaine (African Secret), the French writer and winner of the Nobel prize for literature, Roger Martin du Gard, suggests that illness does have a meaning.

The author is the narrator; …