When should a singer retire? It’s an old, difficult, ticklish question, addressed in these pages more than once. Pianists and conductors can go on pretty much forever. (The string players encounter some difficulties.) Some conductors are barely warmed up by the time they reach seventy. But a singer is more like an athlete, having to wave goodbye relatively early. When to do this waving is an individual decision. Some singers bow out as soon as things start to go awry, or shortly thereafter; others croak it out till the last trump. I think we can say that almost no singer retires too early.

This ticklish question came up in August at the Salzburg Festival: Edita Gruberova sang the title role of Bellini’s Norma in a concert performance (which is to say, an unstaged one). We used to call her a Czechoslovakian soprano; after 1993 or so, we learned to call her a...