Of Moonlight and Bridges, Part 3

In this final installment we look at some chords and harmonic ideas from the Moonlight and Bridge chords, focusing on the most exotic sounds we found last time.

(If none of this makes sense it might be because you haven't read part 1 or part 2.)

Some Hidden Dominants

The four applications we identified last time were Moonlight at the 5 and 7, Bridge at the 4 and 7. These all have a family resemblance in terms of sound and they're pretty far removed from tonal logic (e.g. conventional jazz harmony), which makes them interesting. But it can be hard to keep straight which scales to play at which positions relative to a given root.

Moonlight and Bridge are both based on minor triads, so the easiest sounds to find are Moonlight at the 7 and Bridge at the 7, which basically just reduce to playing a B minor triad over a C root. We can then add the major triads onto the B minors: F major for Moonlight, Db major for Bridge. This could be thought of as a variation on playing B minor pentatonic over C, which is a typical Lydian sound, but since there's no (major or minor) third the sound is much more ambiguous.

The Bridge at 7 seems much more dissonant than the Moonlight there to my ears. One familiar sound within it comes from the major triad; if you're in C and play 7 Bridge, you have B minor and Db major, and you can extend that to a Db7. This is the tritone substitution of the V7, so Db7->Cm provides a little anchor-point of tonal movement there.

The other pair is Moonlight at 5 and Bridge at 4. The way to remember this might be that their relationship is the opposite of the coscale relationship. That is, if you play Moonlight at the 5 and want the coscale, you play Bridge up a tone at the 6. If you want this other arrangement, you go down a tone instead. "Bridge under Moonlight at 5" isn't much of a mnemonic but it'll probably do the trick.

These two are a lot more consonant than the pair at the 7. Obviously Cm-Fm-Gm is all diatonic, so it's really just the two major triads that add a little spice. In this case the Fm is paired with an G major (to make F Bridge), which again can be expanded to G7, giving a traditional V7-i movement (G7-Cm). On the other hand, the Gm is paired with Db major again, and although it doesn't strictly extend to a dominant chord this time (the 7 of Db is B, which isn't in G Moonlight) we still get an echo of the same sound since Db7 would just be the tritone substitute of G7.

There's a lot to get used to here but I think you could consider all this a way to do "dominant-tonic harmony without the third" or "dominant-tonic suspended harmony". In C you have the G7 and the Db7 squirrelled away in structures that don't really sound like that at all.

Deconstructed Triad Pairs

We've seen what happens what we split these hexatonics into triad pairs "along the grain" -- that is, splitting each (hyper)mode into a pair of triads that make it up. What happens when we cut "across the grain" instead, taking two triads from different (hyper)modes? Recall that C Moonlight = C minor + Gb major and C Bridge = C minor + D major. Let's assume the root is C to keep things nice and concrete:

• Moonlight at 5 = G min + C# maj
• Moonlight at 7 = B min + F maj
• Bridge at 4 = F min + G maj
• Bridge at 7 = B min + C# maj

The idea of cutting across the grain is to play just the major triads or just the minor triads from this list, effectively cutting each of the scales in half and recombining those halves to make something new.

One way to think about it is that the roots notes follow the pattern of Forte 3-8, which is a note plus the notes either side of its fifth, e.g. C-F#-G#. This, transposed to B, spells out the notes of the minor triads: B-F-G. The major triads follow the same pattern but a semitone above the root (C) instead of below it.

This approach "deconstructs" the Moonlight and Bridge chords into their triad pairs, then recombines them by triad type. Since it involves several steps, let's do an example with the root A:

• To find the minor triads:
  • Drop down a semitone from A to G#
  • Build 3-8 from there, giving G#-D-E
  • Play the minor triads on each of these: G#m, Dm, Em
• To find the major triads:
  • Slide up a semitone from A to Bb
  • Build 3-8 from there, giving Bb-E-F#
  • Play the major triads on each of these: Bb major, E major, F# major

Since the triads are such simple sounds, these make quite intriguing quasi-tonal chord progressions; on piano they can also be stacked in many different ways.

Some "Across the Strings" Chords

The idea of all this was to get away from triadic harmonies but the ideas we've looked at so far are all triad-based. Let's end with some ways to play the kind of non-triadic chords I tend to gravitate towards these days in each of the four applications.

I hesitate to call them quartal chords because there are plenty of intervals here that can only very tentatively be called fourths, but the idea is to find fingerings that go more or less "vertically" across the strings, making for convenient shapes without containing obvious triadic chords. Most of these are certainly quartal or quartal-adjacent, depending on how strict you want to be:

I've done a lot of this particular kind of harmonization recently and they do all tend to sound a bit same-y so you probably want to use them in combination with other ways to approach these sounds rather than just playing them up and down, but that's probably always true anyway.