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Each diminished chord can have 4 names so what is the rule/convention for determining what to call it - or is there none? It would make sense to me if it were named as the VII chord of the scale/key in which the tune is being played, but that clearly wouldn't work if it doesn't include the 7th note of that scale. Does it depend on the chord inversion, i.e. which note is at the top or which note is at the bottom of the chord?

How about Augmented chords, each of which have 3 potential names?

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  • Sometimes more than 4! E.g. C/B#, D#/Eb, F#/Gb, A/Bbb could be names, depending on keys and functions, of the same sounding dim. chord. Confusing or what? – Tim Oct 2 '16 at 15:42
  • Although fully-diminished chords on Ef, Gf, and Bff would be really rare; the diminished seventh above each would be Dff, Fff, and Afff (!). – Richard Oct 3 '16 at 15:11
  • @Richard - can't think of another reason why bbb would be used! – Tim Oct 4 '16 at 11:34
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For diminished chords, the way the chord is spelled will tell you the root. If the chord is spelled B D F Af, B is the root because it's the bottom of the chord when you stack it in thirds. But if the Af is spelled as a Gs, B is no longer the bottom when you stack it in thirds, but Gs is, so now Gs is the root.

Later in the 19th century, this changes a bit, and composers spell things differently sometimes. If that's the case, run with how the chords functions (=resolves), and provide a label that explains its function best.

As for augmented chords, the process is the same: determine the bottom pitch when you stack it in thirds. If the collection is E C Af, Af is the bottom when you stack it in thirds, so Af is the root. If Af is Gs, suddenly C is the root.

The reason this is difficult is because both of these chords are symmetrical, constructed of consecutive minor and major thirds, respectively. But if you think in terms of thirds, the root should always be clear.

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  • 'When you stack it in thirds' - is there another way to play dim. chords? I'm sure I'm missing something, but it's eluding me! I've seen dims (the same chord, ) in different places in the same song, written as a different name, e.g. Co, then later Ao, and never figured why. These are lead sheets, so maybe that's the clue as to which bass/root note gets played? – Tim Oct 2 '16 at 15:35
  • @Tim: As given in the example, E-C-Ab is clearly an augmented triad, but it's not stacked in thirds. Just like you can play a major triad in an open voicing, e.g. G-E-C for C major; same for diminished chords – Matt L. Oct 2 '16 at 15:38
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    "'When you stack in thirds' - is there another way" Yes @Tim there is another way. Consider these notes from bottom to top - Ab-B-D-F. That's a diminished 7th chord. What's the interval between A-flat and B natural? – MarkM Oct 3 '16 at 19:02
  • @MarkM - If Ab was the bottom, the others would be called Cb, Ebb, Gbb. making 'min3rds' between. Actually, it'll be m3, b5, dim7. Ab and B would be #2. Were the bottom G#, it'll be G#, B, D, F. – Tim Oct 4 '16 at 7:27
  • @Tim That's the point. Af to B would be an augmented second, therefore it wouldn't be stacked in thirds, therefore Af wouldn't be the root. But "stacking" starting on B would result in consecutive thirds, so B would be the root. – Richard Oct 4 '16 at 11:09
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If the 'diminished chord, has a 'minor 3rd, minor 5th, & minor 7th, the chord would be symmetrical in shape / not needing to alter finger position, However: The notes are now, stacked, in 'minor 3rd's.

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    Minor 5th doesn't exist. Can't make a perfect interval minor. – Tim Oct 4 '16 at 7:29
  • Major Triad 1-3-5. / Minor Triad 1-b3-5. Major 7th 1-3-5-7. Minor 7th 1-b3-5-b7th. Half Dim,1- b3- b5 - b7th. Full Dim 7th, 1, b3, -b5, bb7th – Donn Goodside Oct 4 '16 at 22:34

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