I got an email question about Harmonic Minor from a friend; when's a good time to fit it in to general improvisation?

I responded with this. He seemed to find it very helpful. Enjoy.

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Hey Charlie, how's it going, sure here's some info.

You can think of it a lot of ways. Yes, it's a good sub for Aeolian over a minor chord. That's a very straightforward way of thinking about it. 

The deeper thinking for use of a scale, and the sign of a guitar player that really knows his stuff, is to know how a scale is harmonized. Like every scale, Harmonic Minor has modes starting every note of the scale. So yes, there are 7 modes of the harmonic minor scale (just like the major one), and seven chords. For instance, you know the standard Ionian (Major) scale is Maj7, min7, min7, Maj7, Dom7, min7, min7b5. And you probably know by now that the modes over those chords are Ionian, Dorian, Phrygian, Lydian, Mixo, Aeolian, Locrian. So, you know you can play those modes, over those chords (e.g. Dorian over a Min7 chord). 

Harmonic minor, harmonized (so the chords from each note) is (assuming A Harmonic Minor)

- A min/maj 7

- B Min7b5

- C Maj7+

- D Min7 

- E Dom7  

- F Maj7 

- G# Dim7 

You see here, the fifth chord is a Dom7 chord. You might think "mixo for Dom7", and that'd work. But...you're not working with the Major scale, you're working with Harmonic Minor. For spice, why not try the scale that Harmonic Minor suggests over Dom7...which is, Phrygian Dominant. (You can figure out all the modes yourself; just start on the root note of the mode you want, and go up the scale. For instance, if in A Harmonic Minor, the fifth note is E, so you'd go E, F, G#, A, B, C, D, E). 

Note that figuring out the logic of naming of scales, will drive you bezerk, because frequently there isn't any. Don't worry too much about it. Frequently you'll even see the same scale named differently in different books. I try to use the one that makes sense given the structure of the scale, for instance "Dorian #11" (keep reading). 

You also see that, for instance, the fourth chord is a Min7 chord. Again, you might say, "Dorian," which would be D, E, F, G, A, B, C, D. But, do the same thing...in A harmonic minor, you'd go "D, E, F, G#, A, B, C, D". When you play it, this pattern will look like Dorian, but with a #4 (or alternatively, a Lydian scale with a b3). So you could use the fourth mode of Harmonic Minor over Min7 chords, as an alternative to Dorian.

So there's two applications; Dorian #11 (same as #4) over Minor7 chords, Phrygian Dominant over Dom7 chords.

All to be used with taste, resolving properly to the "tone" you're looking for (e.g. The Thrill Is Gone, is actually a Harmonic Minor progression. But if you blew A harm minor all over it, it wouldn't "fit", even though it'd be more or less academically correct. Better to just use the Harmonic Minor as spice, heading for the resolution to the Dorian or Aeolian scale when it comes back to the root). 

Hope that helps, and happy holidays. 

Tim.