Guitarists tend to treat harmony as a keyboard subject. And there’s a good reason for that: harmony is easier to see on the keyboard than on the fretboard. The fretboard is for shapes and patterns; the keyboard is where the real harmonic thinking happens.
History tells a different story.
The Rule of the Octave
The Rule of the Octave is one of the most important practical tools in the history of tonal music. It assigns a standard chord to each degree of the scale, ascending and descending, though the details vary a little from one treatise to the next. It’s usually learned over a bass line that moves by step, but the chords belong to the scale degrees, not to the steps. Once you know what goes on each degree, you can harmonize the bass wherever it goes, even when it leaps. (That’s the subject of the next post in this series.) It was part of the grammar that trained generations of composers in Paris and Naples, and a foundation of the partimento tradition that produced some of the most fluent improvisers and composers in Western music.
And the person who first published it under that name? François Campion, theorbist and guitarist at the Académie Royale de Musique in Paris from 1703 to 1719. His 1716 Traité d’accompagnement called it the règle des octaves.
What’s a theorbo?
If you’ve never seen one, picture a lute with a neck that just keeps going. It showed up in Italy in the late 1500s, when early opera and accompanying from a bass line needed more low end than a regular lute could give.
That neck is there for a reason. With gut strings, the practical way to get a clear low note was a longer string, so a second pegbox sits way up the neck to hold the extra bass strings. They aren’t fretted, so each one plays a single note.
The top one or two strings are dropped an octave, so the first string isn’t the highest one. (If you’ve played a ukulele with a high G string, it’s the same idea in reverse. It’s called re-entrant tuning.)
A secret before it was a book
Campion didn’t invent the Rule from nothing. He credits his predecessor at the Académie, Maltot, with a particular way of making these octaves on the theorbo and the guitar, passed on as “the greatest token of his friendship.” And Maltot wasn’t the only one who knew. Patrice Nicolas points out that a small circle of French musicians, Couperin among them, already knew the “secret” rule before Campion made it public. Even earlier, Nicolas Fleury’s 1660 theorbo method had scale-harmonization models of its own, and so did keyboard treatises like Guillaume-Gabriel Nivers’s (1689).
So the Rule of the Octave wasn’t just a keyboard concept that trickled down to guitar. In France, at least, plucked-string players were part of it as far back as the sources go, and its first publication under that name came from a theorbo and guitar player.
This helps, because I learned about it first from music written for keyboard. Some of it was easy enough to transfer. Some of it was hard or impossible to play without an extra string or two on my guitar.
Why this matters for guitarists
The Rule of the Octave tells you which chord belongs to each scale degree based on where the bass note sits in the key and whether it’s ascending or descending. It’s not a chord progression. Michel Corrette, an 18th-century organist who wrote methods for many instruments, guitar included, called it “the compass of the accompanist, who must always know in what key and on which scale degree of the key he is on, and the chord proper to it…” (Nicolas’s translation).
This is the kind of harmonic thinking guitarists rarely encounter. We learn chord shapes and progressions. The Rule of the Octave offers something different: a way to understand why a particular chord belongs in a particular place, and a default chord for whatever bass note is in front of you, on the spot.
Campion was a theorbo and guitar player. Three hundred years later, the tool he published is still waiting for most of us to pick it up.
I had many of my classical students at least learn a little of this, and it helped. You can see the motion pop up all over the place.
I also liked to annoy my theory-professor friends by telling them to put this in the syllabus. I still wish I’d learned it when I was first learning voice leading and part writing. It would have made things so much easier.
Acknowledgment
François Campion’s 1716 and 1730 treatises are discussed in detail in the scholarship of Patrice Nicolas and Thomas Christensen, and in the Early Music Sources project. Guitarist Nicola Pignatiello has recorded partimento realizations and discussed the Rule of the Octave on guitar (Learn Partimento podcast, 2021). The broader partimento tradition is comprehensively treated in Giorgio Sanguinetti’s The Art of Partimento (2012) and Robert Gjerdingen’s Music in the Galant Style (2007).
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