The Rule of the Octave

At our monthly Singing Group meetings (pot-luck dinners with ill-tuned guitars, folk songs, and old hippies), I've always been awed at the ease with which a good guitarist can cast aside the "Rise Up Singing" song book, and accompany a song using nothing but some magical formula that told him what to play when. The magical formula is actually music theory, and the guitarists at the Singing Group are just music theory magicians.

The Rule of the Octave is a somewhat older spell, but a standard one in lute continuo music. It was quite commonly use in the accompaniment of songs. It is based on the I-IV-V relationship within a scale, but then it expands from there, providing a framework for improvisation which takes into account the prevailing musical expectations of the 17th century (and possibly before).

There are eight parts to the Rule of the Octave, labelled I-VIII, and each part stipulates the manner in which the performer should play a chord required by the scale of the piece. For example, the scale of a piece in G major would progress like this: G, A, B, C, D, E, F#, G. But just playing all normal, major chords would make for a pretty bland accompaniment. Here, the Rule of the Octave comes to the rescue! It says the in the scale, the first chord should be major (the home note chord); the second minor; the third a 6 chord; the fourth major; the fifth also major; the sixth minor; the seventh a 6 again; and the last major. In our G scale, it would look like this (an uppercase letter denotes major, lowercase, minor): G, a, B6, C, D, e, F#6, G.

I imagine that the Rule of the Octave bears great similarity to many a modern-day blues or folk progressions, especially because the Rule sounds good!

Another Renaissance continuo rule is to avoid parallel octaves and parallel fifths like the plague. They sounded very odd to Renaissance sensibilities. Parallel thirds on the other hard, were OK by them!

There are many more rules in Renaissance lute music, probably as rules as there were lute players, and the rules helped create and mold the beautiful intricate and filigreed sound of lute music. However, there is this thing about rules: "The Greatest Excellency in This kind of Performance lies beyond whatever Directions can be given by Rule."
                                                        ----- Thomas Mace, Musick's Monument, London, 1676. p. 217.