I saw a question regarding F# vs. Gb in a given song. The song began in Gb Major then went to F# minor . . . and then it was question as to why the change. Why not just write the song in one Key?

I believe it has to do with the flattened 3rd in Gb caused a problem in the writing. One would have a doubled flat for the third in Gb minor, which is played as "A" on the keyboard. I believe it becomes cumbersome to interpret the notes in the key of Gb major . . . so there needed to be a change to F# minor to make the reading of the music easier.

I hope I made my point clear.

  • 1
    If that was the case, why not write the first part in F# major? 6# instead of 6b.
    – Tim
    May 1 '16 at 7:00

G-flat minor is, as you note, a terribly awkward key, since its relative major is B-double-flat. That is, the third scale degree is enharmonically equivalent to A, but it's actually B-double-flat. That has nine flats in its key signature (or, actually, five flats and two double flats). F-sharp minor has the rather more normal relative major of A major, with a three-sharp signature.

I don't know why the major part of the piece wasn't in F-sharp major, however, since that key has six sharps in its signature while G-flat major had six flats: these two keys are equally awkward.

Perhaps some consideration was given to transposing instruments. For a b-flat instrument, F-sharp major is notated as G-sharp major, with eight sharps (actually six sharps and one double sharp), but G-flat major is notated as A-flat major, with four flats.

  • 1
    Good point about the reading for transposing instruments. If it's going to be that bad, why not write the piece in a more friendly key anyway...
    – Tim
    May 1 '16 at 7:50
  • Actually, for a b-flat instrument, F-sharp major is also notated in A-flat major (and an e-flat instrument in E-flat major). Without seeing the actual score and/or talking to the composer or arranger, any attempt at giving a reason for choosing F# major over Gb major is just guessing. The answers give good reasons for preferring F# minor to the (theoretical) key of Gb minor.
    – user19146
    May 2 '16 at 6:17
  • @alephzero fair enough, for the players of the B-flat instruments, but for the conductor it is probably harder to read a score with the B-flat instruments in A-flat major and the concert-pitch instruments in F-sharp major. I'd much rather have the concert instruments in G-flat major so the visual relationship between the transposing instruments and the concert instruments is as expected.
    – phoog
    Aug 24 '18 at 19:59

TL;DR: It's just better to write since F♯-minor has a lot less signs to write than G♭-minor.

The original tonality you listed was G♭-major; it has six s.
"Converting" major tonality to same-named minor one requires to flatten it triply:
add three , or remove three s.
(Of course, you should use circle of fifths; this is a sort of shortcut)

This means that G♭-minor will have nine s (every note is except for B, E and A, which are ♭♭).

Same pitch and, of course, interval structure has an anharmonically equal F♯-minor.
Except for it has only three s.

Much simpler to write, isn't it?

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