Playing Over Dominant Chords

Q: Like your style.  I need some review of scales to play with regards to how the Dominant Seventh Chord is resolving...functioning as a V chord or just a secondary Dominant (which I would play Mixo or Lydian b7).  If it is resolving to minor I'd play harmonic minor of the letter name of the chord it's going too.

A: here is the basic overview of the dominant scales. Let's take it by how the dominant chord is functioning. When I say functioning, I mean resolving to a I or i chord as in V-I or V-i or G7 - C or G7 - C-7. Non-Functioning means resolving somewhere else or possibly not resolving, as in G7 - F#maj7 or just a static G7 jam. Keep in mind, secondary dominants are for the most part functioning.
1. non-functioning (unaltered) - If the chord is a 7sus4 or 9sus4 chord, the only real choice you have is mixolydian.

2. non-functioning (unaltered) - A plain dominant chord or 7#11 type chord calls for lydian dominant. This is especially true for a dominant chord that  resolves down a half step (b5 sub >>>), as in: G7 - F#maj7.

3. Functioning (unaltered) - A plain jane dominant chord resolving to a I chord. This really depends a lot on your improv skills because theoretically, as the chord has no altered extentions (b9,#9,b5,#9), you really don't have a lot of choices, mixolydian or perhaps the 5th mode of harmonic minor (if it is easy for you to think of the letter name of the chord it is resolving to, that is fine, in other words, G7-C = C harmonic minor. Just make sure not to play harmonic minor over the C chord, just over the G7 chord). You mention that the 5th mode of the harmonic minor scale works when the V chord goes to a minor chord. I personally have never worried about what the tonic chord is (minor, major or dominant for that matter). I don't really think it matters as the tonic chord has a different scale that matches anyways. Regarding the 5th mode of harmonic minor, remember that when the chord is harmonized to its full extent, we get a 7b9 chord.

But, going back to my original point, if you are good at improvising, you can easily use one of the scales designed for altered chords. I'll sometimes use the altered or diminished scale over an unaltered chord because I don't mind the tension it creates before resolving.

4. Functioning (altered) - Altered chords are chords harmonized from the melodic minor scale's altered mode. Chords from this scale have altered 5ths and 9ths in any combination. You could use the altered scale over something as simple as a 7b9 chord or as grandiose as a 7(b5,#9) chord.

5. Functioning (dominant 13 with a b9 or #9 or maybe a #11) - In the case of a 13b9 or 13#9 chord that resolves to a tonic chord, you would want to use the half/whole diminished scale. The chord doesn't even have to be a 13 chord, it could just as well be a 7b9 or 7#9 chord.

Looking at some individual chord might give you some insight:

7 - almost anything goes: major, minor pentatonic scales, mixolydian, lydian dominant, if you have good improv sense, you can use altered or half/whole diminished.

7sus4, 9sus4, 13sus4 - mixolydian only, obviously major pentatonic will work.

9, 13 - same as the dominant 7 chord but you'll have to be a little more weary when using altered or half/whole diminished because of the natural 9 and/or 13.

b5 - whole tone.

b9 - 5th mode of harmonic minor, altered, half/whole diminished.

7(b5,#5, b9,#9) in any combinantion - altered scale, you can play a minor pentatonic scale on the #9 interval as well (for example, a Bb minor pentatonic scale over a G(alt) chord.

13b9, 13#9 - half/whole diminished.

Whether the chord is a secondary dominant doesn't really make any difference. Secondary dominants are generally functioning so can be treated as such. 

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Soloing Over Dominant Chords >>>