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A Piano Beginner: I am playing A Bach Prelude in A Minor:

Bar 1 A C E, Bar 2 A D F, Bar 3 B D G# Bar 4 C E A.

The G# chord has been described as a VII dim (G# dim) and a ii dim 7 (B dim7) giving progressions of 1 4 7 1 or 1 4 2 1. Does anyone have any suggestions as to the "correct" description for Music theory? Perhaps one is Classical and the other Jazz!

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The vii dim is a somewhat-frequently-used chord in the Baroque, especially in first inversion, as here (G#dim/B). This chord is typically used as a substitute for the dominant seventh (e.g. E7 in this case), as it shares the V7's leading tone (the G♯) and it's melodic tendency to resolve upwards towards tonic (A). Indeed, a vii dim chord is essentially a V7 chord without the root.

Technically speaking, a B dim7 chord would have the notes B D F A♭. While G♯ and A♭ are enharmonically equivalent, they imply different voice leading. The A♭ would want to resolve downwards. This difference would have been especially important in the Baroque, to a contrapunctally-minded composer such as Bach.

  • A G# diminished will have the notes G# B D F with the G# resolving to A, the B to C and the F down to E. The ii dim will be half-diminished meaning it'll have the notes B D F A with the B resolving to C and the F down to E the very same way as will a fully diminished G# dim, both resulting in the tonic A minor. – András Hummer Mar 31 '15 at 5:13
  • In this case, there's no mention of an F in the G# dim chord, so it's just a regular diminished chord (G# B D), not a diminished 7th (G# B D F). Nor is there a mention of an A in the chord, so it isn't half diminished. – Caleb Hines Mar 31 '15 at 5:43
  • Sorry @CalebHines, your mention of Ab as a seventh note got me confused. – András Hummer Mar 31 '15 at 8:10
  • Historical note: Bach didn't have the modern theoretical concepts of 7th chords, inversions, chords with missing notes, etc. Following his son CPE's textbook, it would just be described as a 6-3 chord (counting intervals for the bottom note, with the accidentals following the A minor scale). That is the same basic idea as a modern first inversion of the triad on the leading-note, which just happens to be a diminished triad in both major and minor keys. (Note, I said a diminished triad, not a four-note diminished 7th chord in the modern terminology). – user19146 Apr 1 '15 at 19:15
  • True, in line with basso continuo terminology, first inversion chords were referred to as 6-3 chords. But the idea of chord inversions, though not popularized until Rameau (1722), was still a useful working concept that at least some musicians were familiar with. Explicit reference to moving the bass note to a higher voice to create an inversion can be found as early as Otto Siegfried Harnisch (1608) and Johannes Lippius (1610). – Caleb Hines Apr 1 '15 at 20:59
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In A minor, the V harmony, from the E dominant 7th notes, is E-G#-B-D.I see the chord as a V7 with no root. Often the root can be found elsewhere in the bar. So I'd call it an inversion of V7 .

  • It certainly functions as a V7, but assuming the notes listed in the OP are correct, there is no indication of a root elsewhere in the bar, and a rootless V7 is essentially identical to a vii dim. Furthermore, if this were an inversion of V7, it would be a second inversion, which is rarely used in Baroque music, outside of a handful of special cases (e.g. cadential I 6\4), due to it's containing a dissonance (the 4th between the bass and the root). Of course, that goes back to the chord being rootless, and why we name the chord after a missing note, when it already has a perfectly good name. – Caleb Hines Mar 31 '15 at 6:07
  • @CalebHines - You're correct, and your answer is the better one. I wondered about calling it a second inversion, but with a note (E) missing from the sequence, thought maybe not. – Tim Mar 31 '15 at 7:53
  • Thank you all for the responses. The AMEB goes for the vii dim however I find that the ii dim 7 with a missing dominant is common in jazz. Clarification the bar has a left hand pedal point of A3 then right hand B D G# D B so no easy solution. It is probably simplified from the original as it is an Australian Music Education Board beginner piece. – ArgoPete Apr 1 '15 at 4:27

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