I7 - IVmaj7

This vamp you can find examples of, but it’s not crazy common.

The reason is that it has stability issues. Fully-voiced, I7 - IVmaj7 is also V7 - Imaj7 in the relative major, which pulls you out of the key. For example, a G Mixolydian G7 - Cmaj7 vamp is identical to a V7 - Imaj7 vamp in C major, and a V-I is such a powerful sound that it pulls your ear into thinking C is the root.

So you basically only ever see this vamp played as triads (I - IV), to keep it stable — but as triads, both chords are shared with Ionian, so they outline a generic major-ish space without any distinctive Mixolydian color. In fact, occasionally you’ll see songs that take advantage of this to live in the ambiguous modal space between Ionian and Mixolydian. Oftentimes the mode only becomes clear when the melody hits a ♭7, or when a ♭VII chord shows up nearby. In Ionian, the same vamp (Imaj7-IVmaj7) is much more common: two maj7 chords make for a lush, colorful sound. Mixolydian, unfortunately, doesn't get that luxury.

Between the instability when voiced with sevenths, and the blandness when voiced as triads, this vamp rarely lasts long on its own — you almost always see some other kind of harmonic motion, like a ♭VII thrown in, or a turnaround, before too long. You’re almost never going to see a whole song that’s just a Mixolydian I-IV vamp.

However: where this works well is as a vamp in a bluesy section of a tune.

The I - IV vamp is a stripped down of the core vamp of a 12-bar blues (I7 - IV7). But a IV7 chord is not diatonic to Mixolydian. If you do this you’re actually borrowing it from Dorian. (The Beatles do this a lot).

Why doesn’t the 12-bar-blues I7-IV7 have the same stability issues as the Mixolydian I7-IVmaj7? Nobody hears the IV chord in a 12-bar blues as a resolution, instead it just feels like a shift in color, a change in harmonic weight.

Basically it’s because the IV7’s ♭7 (i.e. scale’s ♭3) doesn’t feel like the Ionian root chord. That’s it.

These dominant chords are used as texture, not as function, they’re not pulling you anywhere.

Like a blues, you’ll often see this vamp mixed up with a V or V7 somewhere, which is borrowed from Ionian.

A useful guide to playing a Mixolydian blues

You’ll hear more about modal interchange in Mixolydian later. In this lesson, I want to talk about how, if you’re playing a I - IV in a bluesy way, you have a lot of ways to make the blues sound more or less Mixolydian with your melodic choices.

Note on the exercise below: If you’re not super familiar with how chord extensions work: when I say “It’s a ♯11 over the IVmaj7”, the main thing I’m saying is that this note has a specific, stable, consonant relationship with the chord underneath it and it’s considered fundamentally musically pleasant to do so.

In contrast, “it’s an avoid note over the IVmaj7” means that the note is particularly dissonant, so much so that it changes the feel of the chord underneath. It’s generally considered a bit of spice you want to use in sparse ways, i.e. as passing tones, grace notes, etc.

An exercise:

• Start in blues territory, with a I7 - IV7 vamp
• Start playing the blues scale in the melody.
• This already gives you two borrowed notes:
  • The ♭3
  • The ♯4/♭5

Before we go any further, a quick primer on the ♭3 and the ♯4/♭5:

• The ♭3 is a Dorian borrow. It adds some darkness and some bite, but it sounds great, and it’s really common.
  • Over the I7 chord it’s is a ♯9.
  • Over the IV7 chord it’s a chord tone — the 7th. (Typically the 3rd and the 7th are the “strong” chord tones to use).
• The ♯4/♭5 is also borrowed
  • Over the I7 chord it’s a ♯11
  • Over the IV7 chord it’s a ♭9
    • A ♭9 is a chord extension for a dominant chord. It’s a more tense one though!
  • ♯4 and ♭5 actually do sound different — it’ll sound like a ♯4 (a bright borrow) if it moves up to a 5, and more like a ♭5 (a dark borrow) if it moves down to a 4. It’s idiomatic to play it both ways in a blues, but this difference is another creative dial.
  • (If you want to get technical about it, there are 4 scales being borrowed from here: Lydian Dominant, Mixolydian ♭5, Dorian ♯4, and Dorian ♭5).

Now that you’re playing a blues scale, here are your options for sliding from a bluesy feel to a brighter Mixolydian modal feel:

• ♮2: it steps you out of the blues scale and back into Mixolydian. It’s a subtle brightness that opens things up. It works well over both chords: it’s a 9th over I7, and a 13th over the IV7 and IVmaj7.
• ♮6: this also brings you into Mixolydian. And it also works well over both chords: it’s the 13th over I7, and the 3rd of IV7 and IVmaj7.
  • The ♮6 is a great note to land on for the IV chord, the chord is already pointing there.
• ♮3 (this is the big one): it’s part of the I7 already, but if you play it over a IV chord, you get a Mixolydian IVmaj7 sound. So you get a few interesting options:
  • 1) Play a IV triad in your chordal voicing, and use a ♮3 in the melody. It’s a great note, it’s the chord’s seventh. You probably don’t want to do this for every IV chord — you’ll fall into the stability trap — but as a temporary color change it’s great.
  • 2) Play IVmaj7 in your chordal voicing, and a ♭3 in the melody. If you insist on that ♭3 enough, it causes dissonance, because the ♭3 is an avoid note over a IVmaj7, giving you some bite that’s good in small doses.
  • 3) Alternate between ♭3 and maj3 strategically, whenever you need a small brightness vibe shift. The maj3 is the 7th of the IVmaj7 so it’s a great note for both harmony and melody.
    • Pro-tip: if you let the ♭3 lead you up into the maj3 (for example as a grace note), it actually sounds like a ♯2 and sounds bright rather than dark.
• [Bonus] ♮7: you can also use this, borrowed from Ionian, so it’s extra bright
  • It’s an avoid note over the I7, but you can play it as a quick grace note and it works great
  • It’s a ♯11 over the IV7 and the IVmaj7

I7- vi7

I’m including this vamp here because the vi7 is in a sense the upper extensions of the IVmaj7 chord. This one is an especially rare vamp.

In seventh-chord form, it’s the same as I7-I6 if you take inversions into account — and if voiced like that, I think it would fall under “Camping on I7”. By changing one note you’re not really changing much about the harmony.

In triad form (I - vi), it’s shared with Ionian, and it’s much more common to find this vamp in Ionian. In Ionian, vi7 has a 9 and an 11, and that gives it room to breathe as its own chord with its own character. In Mixolydian, it only has the 11 — the diatonic 9th is the scale’s ♭7, which is a ♭9 over the vi7, an avoid note. This makes the vi7 feel cramped (especially playing melodies over it), and it’s more like a fragment of a larger chord than a chord in its own right. (Having a diatonic ♭9 also, in my opinion, makes the Mixolydian vi7 sound just a bit darker than the Ionain vi7).