Key of C Key Signature has no symbol, so say I was notating music in G Major then wanted to change to the Key of C, how would I show this?

4 Answers 4


Removing accidentals in the key signature is done with the natural symbol. Put a natural symbol on the position of each accidental you want to cancel, and reiterate the ones that are left.

enter image description here

In the above:

  • Cmaj cancels all 3 sharps of Amaj.
  • Gmaj cancels 2 sharps of Amaj and reiterates the one left.
  • Fmaj cancels the sharp of Gmaj and notes the new flat.

As Tim notes in his answer,

  1. adding double bar line before the key change is correct notation;
  2. with many accidentals, the change can get pretty long: enter image description here
  • I can't imagine any composer wanting to modulate from seven sharps to seven flats (or vice versa), but my classical favorite Gustav Mahler did 6♯ → 6♭ in his unfinished 10th Symphony.
    – pr1268
    Commented Feb 21, 2017 at 10:07
  • @pr1268 7 flats is C♭ major, which is the enharmonic equivalent of B major, which is 5 sharps. So from 7 sharps you can modulate to 5, and then modulate enharmonically. It's not far fetched. Ditto for the opposite direction. Commented Feb 21, 2017 at 10:26

You create a new signature containing just of one natural sign on the same line, where the sharp was before, so nothing remains in effect.

See als my answer to closely related question for more details.

enter image description here


It's normal to cancel the previous key signature, so a natural sign (♮) on the F line(s) will be sufficient.

Going the other way (i.e. from C to G) will require merely a ♯ sign on the 'F' line. With more ♯s or ♭s, the new key signature will have naturals cancelling the previous unwanted ♯ or ♭ — a weird key signature with more info than usual!

I tend to put a double barline (both thin) at that point, as it's often the start of a new part anyway, but also to point out the key change clearly … especially in C to something else, or something else to C. Obviously going from lots of ♯s/♭s to C will show up as lots of naturals, though.

  • Not really "weird" with "more info that usual". Historically, naturals were always written to cancel existing sharps or flats in a new key signature (even when going from say 4 sharps to 2 sharps). However the modern convention is that this is only done when the new signature has no sharps or flats - i.e. C major or A minor.
    – user19146
    Commented Feb 20, 2017 at 7:52
  • @alephzero - by weird I meant we're used to seeing only #s or bs in any given key sig. Not a mixture (except for a key change...).
    – Tim
    Commented Feb 20, 2017 at 8:13

Current practice is to insert enough naturals to cancel the previous key signature when moving into the open key. Otherwise just put the new key signature.

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