Deriving a scale from chords
Question: What is this scale? D minor, Eminor flat the 5th, F major, G minor, A7, B flat major7, C# minor flat 5th flat with a dominant 7th. Thank you! - C.


What you're asking is do those chords all derive from a single scale - what key would you be in if you were using these chords. And the answer is: D minor. With one exception all the notes of the listed chords come from the D minor scale. The clincher is the A7, which is the dominant chord of D minor. You might think that the C# found in the A7 chord doesn't belong in D minor, but it is normal in minor keys to raise the 7th degree of the scale to form a major chord on the dominant. If more evidence is needed for conviction there's the C# minor flat 5 (better known as C# dim): those are the notes of the A7 chord if you drop the root (making it a vii dim and also normal for the key). The only bug in the ointment is what you're referring to as a "dominant 7th" in that C# dim chord. If by "dominant 7" you mean a minor seventh, that would be B natural, foreign to the key. Bb would be in the key and would form a C# dim 7, so in the illustration below I show it as Bb:

Yet harmony sometimes borrows from other scales, so if that B in the C# dim chord is natural that still wouldn't take this out of D minor. After all, the normal V7 chord in minor is borrowing from the major scale when it raises its third to become a more convincing dominant, and there are a number of "altered chords" whose nature derives from borrowing notes from outside the key. Music is free to borrow. But this example is relatively clean: but for that possibly-mistaken B natural it's just plain-vanilla-garden-variety-down-home-tried-and-true D minor.

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