i7 → ii7

This is the secondary Dorian vamp. It’s unique to Dorian - these two chords span all 7 notes of Dorian. It’s wistful, thoughtful, bittersweet. It’s also spacious and colorful. It can be a little sad, melancholy - that is, it easily fits those roles if you want it to be, but you don’t have to point this vamp in that direction.

It’s got an unusual amount of stability. Often you’ll hear the bass, or some other sort of drone, stay on the root between these two chords. The scale’s root is the root of the i7 (obviously) and the 7th of the ii7. This is a very cool and useful aspect of this vamp - that it can also be interpreted as staying on the i7 chord and replacing the 3rd/5th/7th with all 3 diatonic extensions, i.e. i7 - i7(9, 11, 13). Similarly, the melody can go ♭7 -> 1 over these two chords, which makes the ii7 chord have some resolution energy.

You’ll often see these sorts of dualities in harmony, where the way a band plays a chord can be interpreted in two ways at once. One way of interpreting this effect is that roman numeral analysis is a leaky broken system which has things it can’t describe. I think that’s wrong. Instead, I want you to entertain the idea that chords in this situation genuinely ARE both things at once, and you’re actually hearing both things at once. They’re like the rabbit duck illusion, or standing in a doorway and being in two rooms at once.

Dualities are interesting because you can often subtly bias your usage toward one side or the other, and this gives you some fine-grained harmonic variation choices.

In Aeolian (natural minor), the ii chord is half-diminished (ii7♭5), which gives it a really strong subdominant pull (to V7, usually). But in Dorian, because the 6th is raised, we get a minor 7th chord on ii - much more stable and usable for vamping.

B-side: i7 - ♭VIImaj7

This is the brighter variant of ii7. It’s more relaxing, ethereal, soft, and lush. It’s also trickier to find it in the wild. I think there’s a few aspects to that.

First, this vamp shows up in rock music, but with triads: i - ♭VII. Without the maj7 of the ♭VIImaj7, this vamp is ambiguous between Dorian and Aeolian. As a songwriter that gives you a lot of freedom with respect to how aggressively Dorian you want your sound to be - you might hear the ♮6 in the melody, or a guitar riff, or a scale run. It’s idiomatic to play with the subtlety here. As a result, examples with a fully-voiced ♭VIImaj7 are harder to find.

Second, when fully-voiced, this vamp sounds a lot like the ii7 - Imaj7 vamp in Ionian (a.k.a. major). My ear will often get confused between the Dorian interpretation and the Ionian interpretation.