I have learned in solfege classes when I was a kid that each sheet music of a musical piece has a key signature made out of sharps or flats.

I understood that this key signature changes when the piece is transposed.

However it is unclear to me why some musical pieces use a complex key signature (e.g Bb minor) when the whole piece could be written a half-tone above, and alterate C and F instead. For instance; "Clair de Lune" from Debussy, which is played mostly on the "black" keys of the keyboard:
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Is it a matter of making it easier to play for the fingers ? Because it seems to me harder to read than if it was using primarily the "white" keys, and alterate few black keys.

Other questions: I remember that when I had to start to study a new musical piece, my piano and solfege teachers were asking to guess and play the related scale and chords.
I didn't understand why at the time. Is it a good practice to 'feel' and integrate the key signature before playing?
Also I remember they asked me to guess the tonality of the music piece. I never really understood why it was so important?

  • 6
    Welcome! Does this answer your question? What's the point of keys other than C and Am? (Short version: if you're using temperaments other than "equal," there are actual differences in the distances between the notes, and for many instruments there are physical differences in playing these keys that might affect the timbre or performance, and maybe composers want these differences on purpose. There may also be symbolic or subjective reasons for a choice of key.) Commented Jun 27, 2022 at 19:16
  • 1
    Everything in 'other questions' should ideally be edited out of here, and asked in a new question. There's a valuable QA to be had there...
    – AakashM
    Commented Jun 28, 2022 at 9:12
  • @AndyBonner: Yes thank you to point out this other post, it is really related to my question. I can see that this topic raised many debates and answers
    – matt
    Commented Jul 4, 2022 at 9:48


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