The first movement's introduction is in C major, but since its main section is in C minor, generally it would be described as being in C minor (even though it ends in C major) - the usual (very general, not exceptionless...) rule is, I believe, to go by the key of the main theme of the fast section of the first sonata-form movement of the piece if it has one - so here, C minor I think. (Though by the same rule, Mendelssohn's 11th "string symphony" should also be in F minor, not F major as usually given. So goes.) Eric 04:03, 23 April 2010 (UTC)
