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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?
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.
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.
