
Originally Posted by
pauln
We need more words to describe pairs of chords.
"Identical" has to mean "the same pitches", so the identical relationship is trivial.
"Equivalent" has to mean the pitches are not identical, but some attribute of sameness is present... but is that equivalence a relationship between the chords (formal similarity) or between the chords and the harmony of the progression (interchangeable)? If the former, what of two chords that qualify as equivalent with regard to each other, but within the context of a tune only one of them sounds right and the other is clearly wrong? If the latter, what of two chords that are nicely interchangeable within a song, but they are clearly not equivalent with respect to each other? In other words, can a chord be a sub of another chord generally, or only specifically with regard to a harmonic context?
Try playing some chords of a tune in reverse, or a song where they attempt to reverse. For example:
I69 | bIIaug | iim7 | bIIIaug | iiim7 | then reverse iiim7 | bIIIaug | iim7 | bIIaug | I69
Notice the problem with the penultimate chord bIIaug? It does not work descending, needs to be bII9b5, right? Likewise, bII9b5 does not works as the second chord ascending, needs to be bIIaug, right? What, and how much, can be said of these two chords before and after they have been placed in context?
Pitfalls of Patterns
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