The genesis of Opus 31
It was noticed early on that Beethoven, contrary to his usual practice, did not dedicate the three piano sonatas Opus 31 to a patron or backer; yet, the notion that they might have been composed without a commission is still doubted today. The circumstances that brought forth those sonatas thus remain unclear, and only the time-frame in which they were composed can be determined with some accuracy.
Of the incomplete correspondence surrounding Beethoven, only one letter has survived that deals specifically with the piano sonatas Op. 31. The letter, dated 18 July 1802, was sent by Nägeli, the Zurich publisher, to Horner, his business partner in Paris. In it he reports that Beethoven has demanded payment of 100 ducats – not 100 guldens – for three sonatas. Beethoven's brother had advised Nägeli to ask for a reduction in fee, but Nägeli himself would have preferred to request a fourth piano sonata, so that he could publish two complete Beethoven volumes in his series, Répertoire des clavecinistes. In the letter, Nägeli adds that he expects the three sonatas to arrive by post on 17 August.
From the foregoing information, the following deductions can be made: First, Nägeli must have written to Beethoven in early summer 1802, requesting that the composer contribute several sonatas to the planned series. Second, Beethoven accepted by letter and demanded a fee, the currency of which Nägeli initially misunderstood, until Beethoven's brother, who often handled his business correspondence, corrected him.