Categorising dominant chords
When it comes to dominant chords we can categorise them in 2 ways:
- Resolving (or functional) dominant 7th chords move to a chord whose root note is a 4th above (or a 5th below). Typically this means we end up on a tonic chord (the I). This is what happens in the ii-V-I progression; the V7 resolves to the I chord.
- Non-resolving (or non-functional) dominant chords have two properties:
- they don’t resolve to a chord up a 4th (or down a 5th), and
- they aren’t preceded by a ii chord.
So, if a dominant chord is followed by a chord with a root a 4th above or 5th below it is a resolving functional dominant. If it doesn’t do that and it’s not preceded by a ii chord then it’s a non-resolving non-functional dominant. However, if a dominant chord does not move to a chord with a root a 4th above or a 5th below but it is preceded by a ii chord we don’t treat it as non-resolving.
So, how can we use this categorisation?
Firstly, when we see resolving (functional) dominant chords we can treat them as having a mixolydian sound and use the mixolydian mode to improvise over them. Simple.
Secondly, if we see a non-resolving (non-functional) dominant chord it is a candidate for being substituted by an altered dominant chord. Possible alterations would be b5, #5, #11, or b13. A very common alteration in this context is the #11. When we improvise over a dominant #11 chord the standard mixolydian mode – which we use over resolving dominants – doesn’t work. What does work is the Lydian Dominant mode.
Just a quick reminder here: in a #4, b5 or #11 are really the same note.
What is the Lydian Dominant mode?
Simply put, the Lydian Dominant mode is the 4th mode of the melodic minor scale. You can think of it in two different ways. The first is to think of it like the mixolydian mode with a #4. The second – and the way I prefer – is to think of it as the major scale with a #4 (#11) and a b7.
R - 2 - 3 - #4 - 5 - 6 - b7
Actually, the term lydian suggests a #4 (or #11) – that’s what you get in the standard lydian mode – and dominant suggests a b7 like in a dominant 7th chord.
Lydian dominant shapes
Here are some scale shapes for the lydian dominant scale that have been working for me. Remember, the #4 and b7 are what give this scale its flavour.