I've been thinking quite a lot recently about what music theorists call harmonic charge – that is, the amount of inherent oomph a chord has. Quite clearly some chords are more surprising, more jangly, have more of a frisson of energy than others. Having some way to diagnose the relative level of harmonic charge is useful for making both arrangement decisions and performance decisions.
My aim in working through this at a theoretical level is not to replace our intuitions. In fact, the primary way of testing the model is testing it against real music and seeing if it feels right. But sometimes (or maybe this only happens to me) we feel a bit lost or indecisive, and having a structure for making musical decisions can help us out of our dither.
So, I think there are three dimensions to harmonic charge. The y axis is the root of the chord’s position relative to the tonic, and is organised around the circle of fifths. The higher up the y axis we go, the more active the chord is. This is like potential energy: the gravitational pull of the tonal system will inherently pull progressions back home, so the further away from the tonic we go, the stronger the internal pull.
The other two axes are binary rather than scalable. The x axis is about the presence of a major or a minor third - the former being brighter, the latter softer. The z axis is about the presence or absence of a tritone in the chord – making the distinction tense/relaxed.
(By the way, I’m aware that my x and z axes may be better articulated at a theoretical level by some kind of formulation about degree of dissonance using set theory. However, I suspect I am not the only musician working primarily in tonal idioms who find a theory developed for the post-tonal avant-garde a bit unwieldy for practical musical decisions.)
I find this model helps in identifying expressive qualities for performance – what the harmony is asking us to feel about a particular moment in the musical narrative. It also helps for making arrangement choices – matching the charge of the chord choices to the emotional climax of the lyrics and/or the focal points of the melody.
This is all about the chords in the abstract, though – the basic sonorities. There are a whole set of arrangement questions about how this relates to voicing and tessitura, but I’ll save them for another post.