Symphony No.33 in B flat major, K.319

While it would be useful to know for whom, or for what occasion, Mozart wrote his Symphony in B flat in Salzburg in 1779, the interesting question is what could have inspired him to make such a radical departure from conventional symphonic form in the first and last movements. The opening Allegro assai proceeds much as expected at first: a lively main theme introduced by the strings with comments from the wind is followed by a vigorous transitional passage and a more lyrical second theme beginning as an exchange between violins and oboes and bassoons. But instead of repeating the exposition, Mozart plunges straight into the middle section of the movement and, far from developing his main theme, introduces a new idea incorporating a four-note phrase that was to take a prominent place in the last movement of the “Jupiter” Symphony nine years later. It is only when he has worked out the implications of this new material that he recalls the main themes.

The more conventionally shaped slow movement opens with a gracious melody on violins and and, in spite of a brief intrusion of minor harmonies and nervous articulation on the strings, it retains its expressive serenity throughout – not least in a lovely little contrapuntal episode for oboes, bassoons and horns without the support of the strings.

The original version of the Symphony in B flat was in only three movements. When Mozart revised the score for a performance in Vienna in 1783 he introduced the present minuet. With its sturdy outer sections and its melodious middle section, it is well designed to offset the Finale – a brilliant, rhythmically impuslive invention with an abundance of tunes, most of them introduced by violins but one of them for oboes and bassoons alone. While Mozart does not go so far in denying convention as to exclude the exposition repeat in this case, he does introduce a new theme in the middle of the movement before, as in the Allegro assai, recalling his main themes and adding a conclusive coda.