A Summary of Some Seventh Chord Vocabulary

Recently I've been returning to early 20th century piano music. The stuff I like often features elements from tonal harmony (such as triad-based chords) combined in non-functional ways. These are also easy to think about and find when improvising. This post started off being about playing seventh chords separated by a semitone but ended up summarizing the wider context of this in my own music.

Starting with minor sevenths, we can play Cm7 (C-Eb-G-Bb) and Dbm7 (Db-Fb-Ab-Cb). Combining their notes and ordering them we obtain the eight-note scale 1-b2-b3-b4-5-b6-b7-7. This is a perfectly legitimate structure but to make sense of it let's thin out the cluster of semitones around the root by removing either the 7 or the b7.

Removing the 7 leaves 1-b2-b3-b4-5-b6-b7, a mode of the Carnatic scale Sarasangi (it's also a mode of (Dharmavati and Chakravakam). Removing the b7 leaves instead 1-b2-b3-b4-5-b6-7, a mode of Neetimati. I don't think Indian scholars consider these to be closely related because the two scales we've founds are modes of them, not the originals -- the 4 is never flattened in Carnatic scales so the relationship would be hard to see from their perspective.

We can therefore evoke Sarasangi by combining Cm7 with Dbm (without the 7), and Neetimati by doing the opposite: Cm with Dbm7.

It's interesting to see Neetimati here because it connects with another important part of my harmonic language, the Coltrane cycle. I think of that as a very "major-based" bit of vocabulary because I mostly think of it as major 7 chords stacked in major thirds, so it's surprising to see the same thing coming from stacking minor sevenths in minor seconds.

Since I mentioned major sevenths, we should see what happens when we stack those a semitone apart as well. Combining Cmaj7 (C-E-G-B) with DbMaj7 (Db-F-Ab-B) give us the seven-note scale 1-b2-3-4-5-b6-7, which is known as the Double Harmonic scale. In Carnatic terms this is Mayamalavagowla, which is also a mode of Simhendramadhyamam and Rasikapriya.

The way I think of this area of my harmonic vocabulary is as follows. There are two "qualities" -- still major and minor, but expanded. They fall into what I'll call "keys" for now, although there are no note-functions, cadences or suchlike. Also, these are being used as pitch collections without any notion of root note, so I'll freely refer to things by names of modes.

The major quality comes from the Coltrane Cycle: major seventh chords moving in major thirds so that their root notes outline an augmented triad. The total collection of notes produced is just six: the Augmented Hexatonic, which can be thought of as two augmented triads separated by a semitone. There are four "keys" in this system, corresponding to the four augmented triads: [C, E, G#], [Db, F, A], [D, F#, A#] and [Eb, G, B].

Related to this is the Double Harmonic scale, which consists of two Maj7 chords a semitone apart. This can act as a major-type tonality in itself or as a way to transition from one "key" to another. For example, in the "key" of C major, we have Cmaj7, EMaj7 and G#Maj7. Moving to the Couble Harmonic pair CMaj7-DbMaj7 provides a pivot to the "key" of Db major. Or it can just work as an ornamentation. Or of course we can go the other way, using the Augmented Hexatonic to move around the Double Harmonic major "keys".

The minor quality comes from the diminished cycle: minor seventh chords moving in minor thirds, which outlines the half-whole (octatonic) diminished scale. There are three of these corresponding to the three diminished chords: [C, Eb, Gb, A], [Db, E, G, Bb] and [D, F, Ab, B].

Again, we have a semitone version, the Neetimati / Sarasangi structure described above, which comes from combining minor triads a semitone apart. This can perform all the same functions in minor keys as Double Harmonic can in major keys.

It would be nice to also have a sonority that combines major and minor. There are various ways to combine one Maj 7 chord with one min 7. Some of these are diatonic and some produce quite large sets of notes.

The ones I like best are those that make non-diatonic seven-note combinations and by far the easiest of these to find is a Maj 7 and min 7 a tritone apart, which gives the notes of Ratnangi or its mode that I call Superaugmented. There's something a bit jazzy about this. If you think of the Maj 7 being the "base chord" we get 1-3-5-b7-(7)-b9-#11-13. This seems to have a kind of "altered Lydian dominant" vibe that you might get from whole tone harmony for example.

I can play for hours with this material. It's easy to hear that something consistent and deliberate is going on but it's also very flexible and can go almost anywhere in a few quick movements. Still, it's firmly rooted in that early 20th century world where tonal harmony is beginning to get repurposed into something new. In consolidating this part of my language I'm also trying to package it up and contain it so I can move into fresh territory without losing it entirely.