But his music seems fusty and sometimes boring because he was saying what had already been said better. Nevertheless, Furtwaengler took himself seriously as a composer and had a natural advantage as a conductor that went beyond his power to perform his own music with a great orchestra. The simple fact is that, when it comes to symphonic music, conductors, who have a panoramic view of scores and ideally possess the most intimate knowledge of the works they perform, are natural candidates to become composers. They have a unique opportunity to develop insight into the other man's music. This affected Bernstein so deeply, that, when he composed, he had to quit conducting altogether, he said, in order to rid himself of all those other people's notes.
Sleeper is in good company believing that.
Yet Previn considers composing invaluable at a minimum as a tool for conductors. That may be why virtually every great conductor, including those not necessarily composers, were nevertheless intimate with the mechanics of composition. Arturo Toscanini, Fritz Reiner, Leopold Stokowski, Eugene Ormandy and Pierre Monteux, though they didn't compose, did arrange suites and reorchestrate works. Serge Koussevitzky was enough of a composer to create a concerto for his instrument, the doublebass, that is still occasionally played. Even the unjustly forgotten Frederick Stock, conductor of the Chicago Symphony Orchestra from 1906 to 1942, composed concertos for violin and cello significant enough to have been performed by such virtuosos as Efrem Zimbalist and Gregor Piatigorsky.