an introduction to chord scales

This is an idea that can be applied to absolutely any non-diatonic chord. Understanding this is crucial if you want to play over changes that aren't just I vi VI (ii) V all day long. What do you do when you encounter a modal interchange chord or a secondary dominant or something else??

The most common thing guitar players do is to play a pentatonic scale that's based on that chord. Sometimes it works, sometimes it doesn't. The reason for that is that our ears want to hear notes from the key that we're in. When a non-diatonic chord shows up, we're thrown for a loop. (That's what those chords are supposed to do.) Something is "out," but we still want to hear something that has relevance to the key.

Here's an example of where a pentatonic scale doesn't really work, why, and how to deal with it. A7 shows up in a tune that's in C.

A7 introduces a new note which is C#. If we play an A7 pentatonic scale over it, we also introduce F#, which is another note that isn't in the key of C. Sure, it's comfortable to play, but it's a note that doesn't fit in. There are many good reasons to play notes that don't fit in, but those notes should be chosen for musical and emotional impact, NOT simply because the pentatonic scale is easy to play on guitar.

So how do you "know" what to play?? The equation is simple. The notes of the chord are most important. The notes from the key that you're in should be used to fill in the scale. In other words, the chord will give you the root, 3rd, and 5th, (and 7th in many cases) of your scale. The key you're in should be used to inform what other notes you use.

Here, we find a scale that conflicts with the pentatonic scale. The pentatonic scale has a natural 6. The scale that we "want" to hear over V/ii has a b6. The pentatonic scale will clearly pull us further away from our key than the chord really intended.

There are countless ways in which this approach to generating scales can be applied. Some of those will create surprising results. Play around with it in your own writing and improvising. Listen to how the new scale behaves once you're comfortable using it.

Brant Grieshaber - guitarist
Guitar Teacher