Thirteen was Beethoven’s lucky number—his lucky opus number, that is. “Opus” means work, and classical composers (or their publishers) frequently number their scores in chronological order using the word. A composer’s first work is “Opus 1,” his next is “Opus 2,” and so forth. Major exceptions are J.S. Bach and Wolfgang Mozart, who did not assign opus numbers. Others created numbered catalogues after the fact: BWV for Bach, K. for Mozart.
Ludwig van Beethoven (1770–1827) labeled as his Opus 1 a set of trios for piano, violin, and cello. Opus 2 was his first piano sonata in F minor. It was the first of 32 sonatas for solo piano, a series that, side-by-side with his 16 string quartets, would graph his progress as a composer.
