Mickey Baker's lesson roman numeral markings

[brwnhornet59]

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The Bbdim chord does sound like a passing chord; it smoothly connects to Amin. So the Gdim and the Bbdim is the same chord with different spelling. I've never thought about passing chords this way. My understanding of passing chords would be Gmaj to G#dim to Amin. Interesting.

I agree that this is a passing chord. Normally you would see Bbdim as a p/c ascending to, or descending from, B-7, but it works effectively descending as if it were.