The altered scale is the seventh mode of the harmonic minor scale and is our key to making a better connection between chords and scales; it contains the following intervals:
1, b2, b3, b4, b5, b6, b7
Wait… a b4? Intervals aren’t normally written this way but for the sake of having consecutive numbers this is how you could write out the intervals in the altered scale. They’re not actually written, or indeed learned, this way of course; here’s how they’re usually written out:
1, b9, #9, 3, b5, #5, b7
Now, this makes far more sense! If you know even a little theory, you can see that the altered scale would work well over altered 7th chords such as 7b9, 7#9, 7b5, and 7#5 because it contains the essence of a 7th chord (1, 3, b7), plus four alterations you could make to it.
The takeaway here is that if we apply this to the scales we already know, they’ll also make far more sense when it comes to matching them up with more complex chords.
How it works
Take the intervals from scale you know well; let’s use the Mixolydian scale, and replace the 2 with a 9, the 4 with an 11, and the 6 with a 13.
You probably learned the intervals of a Mixolydian scale like this: 1, 2, 3, 4, 5, 6, b7.
Write it out like this to understand it on a deeper level: 1, 9, 3, 11, 5, 13, b7.
Here’s how it looks on the fretboard:
The Dorian Scale
The Dorian scale contains the intervals 1, 2, b3, 4, 5, 6, b7 but if we swap out the intervals for their upper extensions, we get: 1, 9, b3, 11, 5, 13, b7 which should help you relate this scale to m9, m11 and m13 chords among others.
Here’s what it looks like on the fretboard:
Try this with any other scales you know and you should be able to break down the barriers between chords and scales, or at least feel a little more confident when you go to solo over more complex chords.