My title is, of course, a begging of at least half the question: we first have to diagnose the right notes as right before we can say that any of them are wrongly played—diagnose rather than merely find: no longer does the fact that a composer puts down a C on paper necessarily mean that he cares two hoots if a C sharp is played instead, or a C-semi-sharp for that matter. And even if he thinks he cares, one takes leave to doubt the profundity of his worries when, in rehearsal, one notices that he does not perceive the difference between the alleged right note and the wrong note he gets instead. Such tone-deafness may indeed be temporary, traumatic—especially if the composer is young, unused to rehearsal, frightened, nervous. But if it happens again and again, in all conceivable circumstances, the least that can be said on the sceptical side is that he must be overestimating the significance of his C qua C.