I like a lot Pink Floyd's "Fat Old Sun" song from Atom Hearth Mother album. Its end is constructed around a quite usual cadence of major chords: "G, D, F, C". I wonder if this cadence is on the key of G (G is at the beginning), or in the key of C (C is at the end). If it is in the key of G, the F note of the F chord would be outside the G major scale, and if it is in the key of C, the note F# from the D chord would be outside the major scale of C. There is neither secondary dominants, so the situation is quite symmetrical.
¿Is there some general rule to resolve similar cases?

  • I was thinking of a similar song with the same chords (Key of G with an F chord used) when I posted this question and got some great answers for the theory behind use of an F chord in the key of G. (music.stackexchange.com/q/29817/16897) Commented Jun 9, 2017 at 4:49

2 Answers 2


If you listen to the whole song, it's clearly based in the key of G. Note that the C chord that ends the final 'repeat to fade' loop always leads back to a G chord. Also note the D chord in my example is a pickup, the chorus progression actually starts with the G chord on 'fat'.

The bVII chord is so common in pop and rock as to hardly need a modulation or 'borrowing' to justify it.

No need to analyse the Am, Dm, Gm on 'The silver sound from a time so strange' earlier in the song as anything more than an attempt to be weird. This IS Pink Floyd after all! Weirdness was their thing.

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I would say that the simple answer is that the song is based in G major but the F chord is 'borrowed' from G mixolydian.

I would expect to see the song written out in two sharps with naturals where the F chord is played.

  • I believe that G mixolydian would include D minor instead of D major Commented Jun 8, 2017 at 22:03
  • Correct. The F major chord is borrowed from G mixolydian, nothing else - it's modal substitution. Commented Jun 8, 2017 at 22:26

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