Let's consider the "black note" between G and A. If this note does not occur in a scale/key, but it nevertheless occurs in a composition based on that scale/key, what are the rules for rendering it G♯ or A♭ if, say, the piece was in C major? I know there are preferences for using the least amount of ink and showing note motion. For example, if the notes which preceded and succeeded it were both G, A♭ would be preferred because it shows the note on a higher line/space and (assuming no A appears later in the measure) a natural is not needed to cancel it. But let's say all things are equal. What rules then govern the spelling of the note?

I chose G♯/A♭ because it occurs as often in flat keys as it does in sharp keys (by contrast, B♭ occurs in every flat key while A♯ doesn't enter the picture until the key signature has 5 sharps) and I chose C major because it has no accidentals in its key signature.

5 Answers 5


The point of choosing A♭ over G♯ is not that it saves ink, but that it expresses properly the function the note fulfills: as a cambiata / melodic movement within a single scale. G - G♯ would imply you're building up tension by leaving the old scale, which would most naturally fit as the raised degree of a dominant, i.e. E₇ as the dominant to Am, with the G♯ leading up to A.

So, that's really the main question to ask: what effect does this note have? Would it sound fitting if you resolved it to A? Then it's a G♯. If it sounds more sensible if you resolve it to G or even G♭, then it's an A♭. (Regardless of whether that actually happens in the piece.)

This, or any other rule, won't work always, but it's IMO the one that gets most to the heart of what those accidentals are really about.

Of course then the next question would be: is it really G♭? If it resolves to F♯, then the preciding note would again more sensibly be G♯.


There's a thing called the Harmonic Chromatic Scale, which works on the principle that you leave the tonic and 5th 'clean', every other note occurs twice. But I really wouldn't worry about it! Write chromatic runs with sharps going up, flats coming down. Where the harmony is clear, try not to obscure it - e.g. if there's an E7 - Am harmony make the E7 LOOK like an E7 with a G#. If it's F, Fm, C, give Fm an Ab.

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In addition to Laurence's answer I would like to add something I always taught my piano students, when I was still teaching. If a black note occurs in a triad or 7 chord, remember that there must be a letter missing between every two notes. So, if there's a G#/Ab between an E and a B, then the black note must be G#, because you have to skip the F and the A. (You can't have no letters missing, and you can't have two between two adjacent notes in the chord.) Likewise, if there's an F below the black note, and a C above it, the black note must be Ab, because you have to skip the G and the B.

The same principle works with 7 chords. There has to be a letter missing between the 5th and the 7th. So an Amaj7 chord has to have G# as the 7th tone, because there has to be a letter missing (and only one) between the E and the 7th note.

This works whenever a note in question is part of the harmonic pattern. If it isn't, use Laurence's solution.

  • I'm not sure this helps the OP. Their note doesn't seem to occur in a simple triad or 7th chord, and if it's not then this system fails. It fails in a lot of interesting situations in fact, for instance add2 chords (which may be sure be problematic on inexact instruments like piano, but can sound awesome when e.g. sung in just intonation) have no “letter between the notes”, nor do inversions of seventh (possible diminished-seventh) chords. And this scheme might give nonsensical results if you e.g. apply it to a sus4 chord as “B♭ D♯ F”, which is just generally bogus. Commented Mar 9, 2017 at 23:06
  • I think I covered that in "Where the harmony is clear, try not to obscure it - e.g. if there's an E7 - Am harmony make the E7 LOOK like an E7 with a G#."
    – Laurence
    Commented Mar 10, 2017 at 13:09

Depends on both the harmony and direction. For example, some hold that the Eb in borrowed V9 of V of c minor, used in C major (that is D-F#-A-C-Eb) is notated as Eb if it goes to D, but as D# if it goes to E. However, some theorists insist that no matter what direction it goes along, the minor-key-borrowed V9 of V is still the same chord, and Eb must always be notated as Eb, as if it is the V of g minor. So the matter is still controversial. Moreover, in a twelve tone composition, the one that is more succinct is used; there, all 12 notes are created equal. So, no, there is no compulsory rule, but convention is what I said.

  • 9th note of D9 is E. b9 note of D is Eb. Should it be 'Vb9 of V'?
    – Tim
    Commented Mar 10, 2017 at 7:03

The 7th is flat. So it seems pretty natural to make the G#/Ab a flat. But if your just trying to make the augment then you'll just make the sharp because that's the agreed way that it's always done.

  • 4
    As it stands, this answer seems confusing. It needs expanding upon to make more sense.
    – Tim
    Commented Mar 10, 2017 at 15:10
  • This comment of Tim is not mocking you, it's a try to help you and give an advice. Your answer is short, but unclear. Yes, b7 is flat, but on what are you referring? OP doesn't ask about the 7th. He asks why do we differ and decide that the black key is Ab or G#... you're not answering this question. Commented Apr 15, 2020 at 20:49

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