In relation to How common is the complete circle of fifths progression? which describes some examples of the complete circle of fifths progression (a consecutive I-IV-VII-III-VI-II-V-I progression), apparently this full progression is more commonly found in minor keys rather than a major keys. Is there any reason for this? Explanations are greatly appreciated.
The reason why the circle of fifths progression works better in minor than in major is the higher flexibility of minor, in the sense that more notes are available than in major, without the need for alteration. In minor, all notes from natural, melodic, and harmonic minor are available without leaving the key. This is not the case in major. The consequence is that for some of the chords of the circle of fifths there are several options, depending on whether the notes are taken from natural, melodic or harmonic minor. For the circle of fifths progression in minor, the chords are chosen such that they result in the most pleasing progression, which cannot be done in major.
The problematic VII chord in major (half-diminished), which is the II chord in the relative minor key, becomes naturally embedded in a II-V-I progression at the end of the circle in minor, but not in major. Have a look at the progression in A minor:
|| Dm | G | C | F | Bm7(b5) | E7 | Am ||
The tritone interval from the root of the F chord to the root of the Bm7(b5) chord is not perceived as too weird because the II-V-I at the end is such a pleasing cadence. Furthermore, the Bm7(b5) leads logically to the E7 which resolves to Am. Now look at the corresponding progression in C major:
|| F | Bm7(b5) | Em | Am | Dm | G7 | C ||
First of all, the tritone interval in the bass occurs immediately but it is not 'justified' by any nice resolution, because diatonically the E7 chord is not available anymore. Second, the Bm7(b5) doesn't function anymore as a II in a II-V-I progression in minor, yet this is (almost) the only thing that it is good at.
In sum, in minor the Bm7(b5) chord is embedded in a natural II-V-I progression, and that's almost its only right of existence. In major, there is no such option (at least diatonically), and therefore this slightly strange chord keeps dangling somewhere in the progression because on its own (outside a II-V-I) it can't properly resolve. This is why the circle-of-fifths progression sounds much more pleasing and logical in minor than in major.
One big chord in question is the 7. In minor, if unaltered, this chord is a subtonic chord, as opposed to its altered version where it is the leading-tone chord. So in C minor, diatonically, the 7 chord (subtonic) is Bb D F, while the leading-tone chord would be B D F.
You can hear right away that in the minor mode, the subtonic leads just fine to the mediant chord (i.e., VII - III, or Bb major to Eb major in the key of C minor). On the other hand, the leading-tone chord really doesn't do so well leading to III (B dim to Eb major is tricky).
Now in major mode, you don't have these two choices (at least diatonically). The leading-tone chord in major does not lead to iii very well (B dim to E minor), nor does the subtonic (Bb to E minor, Bb being altered in major mode).
And so, in minor mode, there is a more natural transition from VII to III, compared to vii dim - iii or VII - iii in major.
Probably because that elusive dim chord moves towards the V then to i in minor better.Or it sounds better as a m7b5 as a 4 note chord, giving the same effect.In major, it sounds quite weak without the root (a 5 note) which would make it a V7.
The issue is entirely the diminished chord (or half diminished seventh chord). Unlike the rest of the chords, the root leaps a tritone instead of a perfect fifth. This makes it the weak link in the chain.
In a minor key, it is the 2 chord, which comes fairly late in the progression, after the direction that the progression is going has been well established. In a major key, it is the 7 chord, which is the second chord in the progression, which means it comes before any progression has been established at all. There is no built up momentum behind it.
Furthermore, coming out of a diminished chord is also quite weak. The diminished chord wants to resolve by going up one scale degree (
vii°-I), rather than follow the circle of fifths. This reduces any momentum even further. The minor progression, however, makes up for this by following the diminished chord by the strongest chord progression available: the
V-i. The major progression,
iii-vi, is much weaker.