Mozart wrote over fifty symphonies, but only two of them, the 25th and 40th, are in a minor key. Interestingly, those two are some of his most highly regarded and most often played works. Why did he write only two symphonies in a minor key?
One argument might be the minor keys are, at least now, considered to have a more doleful sound and the time of the 40th Mozart was having financial problems, but were minor keys considered doleful in Mozart's time the way they are now? Did he ever write anything giving a clue to his motivations in his compositions?