Yesterday I wrote about the modern modes and explained how to work out the pitches for any given mode by finding the parent major scale. For example, a D dorian is the same thing as a C major scale beginning on D, but it’s also like a D major scale with a lowered 3rd and 7th. If this stuff is new to you you’ll want to go back and read through that article before you read this one.
Today I’m going to show the relationship between the modes and certain chords. For this post I’ll use the modes in the key of B flat major.
If you take the root, 3rd, 5th, and 7th of each of the modes you will get a chord. For example, if you look at those pitches on the B flat major scale you will get a Bbmaj7 chord.
As it also turns out, this scale sounds pretty good over that chord. Here are similar examples using modes in the key of B flat major.
If you go through each of the modes like this you’ll end up with four basic chord qualities.
Major 7th chords – ionian, lydian
Minor 7th chords – dorian, phrygian, aeolian
Dominant 7th chord – mixolydian
Half-diminished 7th chord – locrian
An improviser looking for notes to play over a given chord can select a mode that corresponds to those chord qualities. Some modes fit a little better than others, depending on the context. For example, the dorian mode sounds particularly consonant over a minor 7th chord, where the phrygian and aeolian modes have certain notes that clash against the chord. This can be exploited, if you want to add a little tension to your line, but there is a certain harmonic logic to which mode to choose. In order to fully grasp this, consider the most common chord progression in jazz, the ii-V-I.
Selecting a scale for the F7 chord is easiest, because there’s only one choice for this chord using this method, the mixolydian mode. We’ve got a couple of different choices for the Bbmaj7 chord, but since we’re in the key of B flat, the ionian mode (same as the major scale) is going to relate closest to our key center. We’ve got three different choices for the Cmin7, but let’s consider our key center again. Since C is the ii chord of our key center (Bb), C dorian will keep the mode diatonic to our key of B flat. Notice also that F mixolyidian is also diatonic to B flat. An improviser can “blanket” that entire chord progression playing a B flat major scale.
Here is a common extension of the ii-V-I progression, moving to the IV chord.
Rather than selecting the major scale sound over the Ebmaj7, many jazz improvisers prefer to use the lydian mode instead. It’s still diatonic to the key of B flat, it contains all the chord tones, and also has a really interesting color tone, the raised 4th above the chord’s root (A natural, in the case of Ebmaj7).
Once you get the grasp of how this works, you will notice that many common chord progression (in both jazz and classical) have a diatonic relationship of this sort. For example, we could add an Emin7 to Amin7 before the above chord progression (iii-vi-ii-V-I-IV in B flat). We could use the dorian modes for Emin7 and Amin7 like we did for the Cmin7, but E phrygian and A aeolian (natural minor) make for logical choices if you want to your melody to relate directly to the key center.
If all chord progressions were diatonic like this and if all improvisers simply played the parent major scale over them the music would get boring pretty quickly. Still, they make for a good first step towards understanding how to achieve a particular sound. Remember, music theory isn’t a rule to follow or a system to practice, they are symbolic representations for particular sonic colors. Practice with ear training in mind. Record yourself and listen back with your attention on the sounds of these modes. The point isn’t to force yourself to improvise using “correct” notes, but to memorize the aural qualities they have so that when you imagine a line in your head you can instantly play it.