The rule of the octave (RO), or regola dell’ottava, is a term used when referring to the harmonisation of the major and minor scale in the manner of the partimento tradition. The regola instructs us how to harmonise each degree of the scale, both ascending and descending, in a unique relation to the preceding or following chord. This gives each scale degree it’s own distinguishable place withing the tonal hierarchy of the key.
Guitarist François Campion (1686-1747) was one of the first to mention a rule of the octave, and after his there has been a number of different variations of the RO, but during the 18th century a standardised version became more prominent than the others. This version was included by Fedele Fenaroli (1730-1818) in his Partimenti ossia basso numerato, and will be used as our first example.
We will begin with looking at the major scale and it’s harmonical structure. The scale degree is indicated with a number within a circle ➀ ➁ ➂ etc. And above the note system there will be one or more numbers, indicating how many notes is to be played and the distance of the tones in regards to the bass. For example, if the bass note G has the numbers 3 and 5 above, one is supposed to play the third and fifth interval above the scale degree, G – B – D.
One important thing to take notice of is the order in which the notes are presented, in other words the chords inversion. Since Fenaroli did not intend that the RO presented in his Partimenti ossia basso numerato to be played on the guitar, but rather the cembalo, we should take into account that some of the instructions does not play well on the guitar.
Nota bene
Figure 1 and 2 has been transcribed from f- to g clef to accomodate for the guitar.
Notes on the major scale degrees
➀ is a perfect consonans.
➁ is an inversion of ➄.
➂ is an inversion of ➀.
➃ is a perfect consonans when ascending. Inversion of ➄ when descending.
➄ is a perfect consonans.
➅ is an inversion of ➃ when ascending. Passing dominant to ➄ when descending.
➆ is an inversion of ➄, with an added 7th when descending.
➇ is a perfect consonans.
Fig. 1
Rule of the octave as instructed by Fedele Fenaroli in Partimenti ossia basso numerato.
Fenaroli gives us two alternatives on the ➃ and ➆, where players may chose the one that suites the context of the music best. For example, when playing diminutions with three note figuration, the option with only three notes ought to suite the diminution pattern best. Or if the player choses a contrapunctual form, the option with four voices might suite better for a richer harmony. When choosing to play in a contrapunctual style on the guitar, a three part voice leading is by far easier to achive. Four voices is easier to achive when playing diminutions, for example in an arpeggiated prelude or caprice.
Nota bene
a) From this point on the circled numbers will be left out in the notated figures.
b) The sharps within parantesis are there to clarify that the chord on that scale degree borrow notes from the major scale. For example, the ascending ➁ has a sharp sixth in the top voice, which serves as the major third of the dominant (➄).
Notes on the minor scale degrees
When playing the minor scale, it is most common to use the melodic minor scale with it’s augmented second between the ➅ and the ➆ when ascending the scale, and the flat ➆ when descending it.
➀ is a perfect consonans.
➁ is an inversion of ➄.
➂ is an inversion of ➀.
➃ is an inversion of ➁ when ascending, inversion of ➄ when descending.
➄ is a perfect major consonans.
➅ major when ascending, passing dominant to ➄ when descending.
➆ is an inversion of ➄ when ascending, and minor (♮) when descending.
➇ is a perfect consonans.
Fig. 2
Rule of the octave as instructed by Fedele Fenaroli in Partimenti ossia basso numerato.
This harmonic structure is the basis of which we can find alot of guitar music from the late 18th and early 19th century is built upon. The RO is a good starting point when learning to improvise preludes and cadenzas, as it gives the player a great tool for navigating the tonal landscape.
In the guitar litterature of the 19th century many authors didn’t refer to the harmonisation of the scale as the RO, but used other terminoligy such as Gammes Harmoniques (harmonic scales), accompaniment of the scale, or the Allgemeinen Regel für die Begleitung (the common rule for accompaniment), can instead be found. Even though the term “rule of the octave” is absent it is more or less the same way of harmonising the scale.
In the following pages we shall take a closer look at, and compare three composers representing three different styles of 19th century music.
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Karl Michelson 