Beethoven has an Opus 81a (Piano Sonata No. 26) and Opus 81b (Sextet for Horns and String Quartet).

Why is this Opus divided/labeled this way, instead of split into Numbers as opus cataloguing usually dictates?

  • Hi! After investing on this question, I found that there is no strict rule about Opusing a composers work. Sometimes you'll seem to find a rule until you find a counter example...
    – Bebs
    Commented Feb 13, 2018 at 10:45
  • @Bebs That's true (and also true of most things in music), but why this particular deviation from the norm? Commented Feb 13, 2018 at 17:53

2 Answers 2


This is mainly a historical accident, arising from the fact that the pieces were published by different publishers. The piano sonata was published originally by Breitkopf & Härtel as Op. 81 in 1811. However, the publisher Simrock had also released the horn Sextet as Op. 81 in 1809 or 1810. It was only later that they were renamed Op. 81a and Op. 81b in order to avoid confusion.

Calling them No. 1 and No. 2 would indicate that the pieces are part of a set. In this case, there is no such connection between the them.

Source: Stewart Gordon, Beethoven's 32 Piano Sonatas: A Handbook for Performers.

  • I logged in for the first time in quite a while just to give you that green check. Thank you very much! Commented May 13, 2020 at 15:33

My best guess is, that numbers are used more frequently, when grouping very similar works, for Beethoven the violon sonatas, the string quartets op. 18 and op. 10 piano sonatas.

Here there is not much common beneath the time of creation (1810).

As the piano arrangement of the violin concerto shows, directly derived works also receive a letter, as op. 61a opposed to op. 61.

  • Maybe I'm misunderstanding, but it sounds like you're contradicting yourself; "directly derived works" are more similar, not less, correct? Commented Aug 13, 2018 at 23:36

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