I have listened to the Hammerklavier Sonata many times, sometimes while following the score, and I have noticed that, in the second movement, there is a change in the key signature for just a little. This has baffled me for quite some time.

I checked different editions of the score available on IMSLP, and all of them contain this change.

I am referring to the change that happens when the tempo changes to Presto in the image below.

From what I can tell, the music modulates from Bb major to B minor. Then the key signature changes to C major/A minor, only to go back to the 2-flat key signature.

IF I was the composer, I'd change the key signature to B minor in the third bar of the image, use A-sharp instead of B-flat, and then I'd change the key signature back to Bb major in the Tempo I mark.

enter image description here

Is there any special reason why Beethoven wrote it like this?

  • This is really a fantastic question about a fantastic composition I only knew the title but never listened to it before. now I have to work on it for some months analzing it. I won’t be able to play it but I will study it. thank you for the input. But why just wondering about this two bars? I could ask you the same question everya second measure: Why did he like he did? so is there an objectif answer ... except the reference the other section where the same passage appears again? Commented Nov 11, 2019 at 18:20

4 Answers 4


It seems to me that the purpose of the notation is to show the performer how to interpret what is happening.

After the ambiguous passage, we do arrive at the start of what appears to be a new section, in a new key, with a new rhythm (cut time not 3/4), at a new tempo (Presto) - though it's not quite clear what the new key actually is, since we only hear one pitch, B natural, and that doesn't sound like the tonic.

And then a big Monty-Python-foot-like B flat comes down from the sky and says, "Nope, we're not having any of that, thank you very much - the end!!"

Without the key change, the whole passage could be interpreted as just "fooling around" with no real intention of going anywhere at all.


The key signature change aligns with the Presto, to emphasize that the harmony at that point is still B D F#, because the bare B's aren't enough to show that. His other late sonatas also modulate briefly and surprisingly, but with more than just unisons, so they needn't compensate with such brief key signature changes.

Changing key signatures in the third bar of this excerpt is too soon. There, the B natural's effect is "huh, what?!" and the ensuing alternation, deliberately prolonging the listener's confusion, is a Webernesque condensation of Berlioz's tritone-apart orchestral hammering in the Symphonie Fantastique, if I may be excused two anachronisms... but the alternation of not just pitch but register AND dynamics is pure Webern. Only after that alternation has dissipated, can we consider "what key" we've landed in.

  • 2
    Oh not another Webernesque condensation of Berlioz's tritone-apart orchestral hammering
    – Strawberry
    Commented Nov 11, 2019 at 19:13

Well, we don't know Beethoven's considerations. I am wondering why Beethoven actually did make a key signature change which only lasts four bars. For such a short while you would often use accidentals instead.

But since there is a key signature change I would say it makes sense that the change happens at the same time as the time signature change and the tempo change. It underlines the Presto section.

  • Yes, but by undoing the 2 flats, it seems that he's implying either C major or A minor tonality... That's why I basically asked this question. Why not introduce the B minor key signature, instead? Maybe we will never really understand...
    – George
    Commented Nov 12, 2019 at 15:43

A look at primary sources would make sense in this instance. Regardless, as Gregory Proctor discusses in his important Ph.D. dissertation ("Technical Bases of Nineteenth-Century Tonality: A Study in Chromaticism," Princeton Univ., 1978), enharmonic tones such as B-flat and A-sharp do not have the same signification in the music of common-practice tonality. They represent the same frequency but different fields of tonal forces. Note Beethoven's dynamic markings and registral shifts in measures 3-5, which help introduce the B-natural as if "from elsewhere," presumably not colored as a flat supertonic (C-flat) of the established major key, but rather as an intensely dissonant (ironic?) foreshadowing of the six-measure B-minor area before the double bar.

The clash between B-flat and B natural his of special importance in the first movement of the work, as well. There it helps defer the climax, which in most sonata forms occurs towards the end of the development section, until the beginning of the recapitulation — to rare and striking effect.

  • This question is discussing the scherzo-and-trio-form 2nd movement, not a sonata-form movement of the Hammerklavier Sonata.
    – Dekkadeci
    Commented Dec 23, 2020 at 13:37
  • @Dekkadeci thank you for pointing out this clumsy slip. I’ve revised the answer accordingly.
    – Tekhnee
    Commented Dec 24, 2020 at 14:18

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