American born and bred, he feels a constant outcast. His conducting mentors — Fritz Reiner, Dmitri Mitripoulos, Serge Koussevitsky — connect him to the old Continent. He misses out on war service, the forging fire of his generation. Like Aaron Copland and most of his closest friends, he is Jewish and politically on the Left. There is mention of "the party" in letters of the 1940s, though Bernstein would always deny he was a Communist. In an effusive affidavit, sworn in 1953 when Senator McCarthy inflicted terror across the arts and Bernstein had his passport withdrawn, he declares: "I am not and never have been a member of the Communist Party, nor have I ever subscribed to communist doctrine or ideology." He adds: "I have in the past spoken out against the inhibitions imposed upon creative artists, particularly composers, under the Soviet regime." Do we hear an ironic snipe at his own, American inhibitors?

His outsiderness is exacerbated by sexual duality. He is attracted more to men than to women, giving restless encouragement to both — except during brief chastity breaks. He sees a New York shrink, "the Frau", whom he shares with his lover, the clarinettist David Oppenheim. The Frau tells him: "In your dreams there is confusion, you are not able to go where you have to go: two simultaneous engagements and so on. You are seeing Felicia and the day she leaves you have to see a boy."

Felicia Montealgre, his Chilean fiancée, agreeing to marry him, accepts that "you are a homosexual and may never change — you don't admit to the validity of a double life." Both the shrink and the wife have got               him bang to rights. Bernstein, however, eludes all attempts to limit him to any single affinity.

Music is his ultimate ambivalence, riven between mass popularity and classical esteem. Koussevitsky condemns On The Town in 1944, so he writes nothing more for Broadway while the old man is alive. He completes West Side Story in 1956 and, the ink still wet, signs on as music director of the New York Philharmonic — one foot in both camps, never openly acknowledging the possibility of a double life. 

Despite, or because of, his desire to be all things to all men and women, his is one of the great American success stories. His Philharmonic era brings US composers universal recognition. He creates a cult of Gustav Mahler, provokes argument and attention and educates a mass audience via the new medium of television in how music really works. To eight-year-old kids on Saturday morning, he makes it seem like fun.

After 15 years, he drifts off, craving other confirmations and consolations. He takes no other job after the Philharmonic. He leaves Felicia for a man and returns to nurse her when she is dying. His later concert works miss the mark by an ever-widening mile. He tells the song composer, Ned Rorem: "The trouble with you and me, Ned, is that we want everyone in the world to personally love us and . . . that's impossible."

Even in decline, he could light up any room on earth. I remember an affair at the Savoy electrified by the glimpse of that ruined, whisky-capillaried nose poking round a doorway. His death in October 1990 hushed Manhattan to a moment's silence. Weeks before the end, he receives a letter from his aged mother, Jennie. "Dear Son," she writes, "I have confidence in you that you are on the right track." Curb the Jewish mother jokes: within these compelling letters lie eternal, at times unbearable truths.