Modal interchange from Phrygian Dominant

Modal interchange, in short, is what you call it when:

• A song is “in a mode” (a 7-note scale, usually), AND
• An instrument plays a note that’s not in those 7 notes - this note is called a “borrowed note”
  • Either in the melody, or in a chord (in which case that chord is called a “borrowed chord”)
  • Conceptually this note comes from another mode with the same root - either you’re raising or lowering a scale degree.

By far, the most common mode that Phrygian Dominant borrows from is Phrygian, with a ♭3. It’s so common and so useful that you’ll hear the interchange more often than not. In fact you've already heard it in some of the examples so far.

When this happens we’d call that ♭3 a borrowed note. Phrygian has all the same notes as Phrygian Dominant, except for that ♭3 replacing the ♮3.

There's a couple common ways this tends to happen:

• Sometimes you borrow a ♭3 in the melody.
• Sometimes you use this vamp: I7 - ♭IImaj7 - ♭III [- ♭IImaj7].
  • Notice that I’m writing ♭III as a triad - why? As a seventh chord, it’s a dominant 7th chord - a ♭III7, with the scale’s ♭2 serving as the seventh. When you voice this seventh, it means there’s a tritone in the chord, and inherently more crunch. To my ears, ♭III and ♭III7 sound fairly similar in context, but distinct enough that I think of them as distinct things. There’s probably songs where you can substitute your ♭III for a ♭III7 with only a small color change, and probably some song where doing that will add too much tension.
  • A common alternate move is to use a ♭III6 chord, which is an inverted i7 chord - adding a sixth adds color without running into the same complication.
• Playing between Phrygian and Phrygian Dominant is also common. The way you do this is just by avoiding playing a ♭3 or a ♮3 - keep this ambiguous.

Why does borrowing from Phrygian work so well?

1. Over the I7, the ♭3 is a ♯9 interval - an interesting chord extension
   • This is written as I7♯9 - this kind of chord, a dominant 7♯9 (pronounced “dominant 7 sharp 9”), is also known as a Hendrix chord
2. Over the ♭vii7, the ♭3 is an 11th, and over the ♭IImaj7 it’s a 9th - these are both great, consonant extensions
   • The diatonic ♮3 (diatonic means “no borrowed notes”, or “only consisting of the 7 notes in the scale”) is what’s called an avoid note (a jazz term) over both ♭vii7 and ♭IImaj7 - which means it’ll make the chord sound extra tense. It’s an interesting flavor, but it changes the chord quality (the technical term for “type of chord that it is”) and the nice inherent consonance of these two chords.
   • So by using a ♭3 instead of a ♮3 you’re softening this bite a lot.
3. You can use a i7 in addition to the I7
   • (♭III6 is an inverted i7)
4. The “ambiguous space”, so to speak, between the two modes is a very fruitful place to hang out
   • It’s kind of like a neutral intensity. Not the threatening darkness of Phrygian, nor the power-brightness of Phrygian Dominant.
   • It’s super easy to do: just play the normal vamps, and don’t play the third of the root chord
     • Often this looks like “the bass is playing the roots of the chords and little else is happening on top of it”
     • A I7sus chord works here too
   • Melodically, you can use the minor pentatonic scale, the ♭2, and the ♭6 to play between the two scales - and only dip into a ♭3 or a ♮3 when you want to polarize the energy a little more.

Other modes

• ♮2: Mixolydian ♭6
• ♯4: Phrygian Dominant ♯4
• ♭5: Locrian Dominant
• ♮6: Mixolydian ♭2
  • There's an example of this below
• ♮7: Flamenco

Since Phrygian Dominant tends to be played very modally (limited harmonic options, unlike say Ionian or Aeolian), you don't see some of these particulaly often. I'll list examples in the encyclopedia.

An honorable mention: if you play a V7 chord, you borrow both a ♮2 and a ♮7, and the mode you're borrowing from is Harmonic Major. You'll notice that this has a different sort of bite than the much more common move of being in Aeolian and borrowing a V7 from Harmonic Minor.