Our metric is the ease or difficulty a listener has in understanding the two lines as separate entities, in keeping track of them as they proceed, in following their courses and comprehending those courses as distinct. Certainly it is a valid goal to write counterpoint that is deliberately thick and tangled, immersing the listener in a jungle of melodic ideas where independence is less important a value than denseness or maximality of texture however, for the purpose of this essay I want to consider only two-voice counterpoint where clarity and perceptual independence of the lines is treated as the fundamental aesthetic goal. Specifically which elements of the past should be preserved, and is the parallel octave restriction among them? There’s room for questioning too if the composer says, “I want to write the best counterpoint I can, no matter what style it happens to fall in, and I’ll adopt any rule, or break any rule, to make the counterpoint as good as possible.” Of course this raises the question of what goodness means as applied to counterpoint. There is cause for deeper questioning in a third scenario, when the composer aims to look forward and back at the same time, writing in a style that combines elements of the past with new ideas. First, the composer can say, “I aim to look back and write counterpoint that is idiomatic to some stretch of the Renaissance or the common practice period, and since the composers of those times avoided parallel octaves, I must do so too.” Second, the composer can say “I am a 21 st century person, writing in a fully contemporary style, and there’s no need for me to adopt the rules of the past, particularly given that composers before me have already broken those rules to such great effect.” In each case, any detailed inquiry into whether the parallel octave restriction serves a valuable musical purpose can be cut short, and the composer may simply embrace the attitude of whatever style he or she wishes to work in. Stepping outside of an academic context, there are two broad scenarios where a composer need not think too deeply about parallel octaves but can simply adopt an appropriate blanket policy. The teacher may say “First you need to learn the rules before you can break them” but the question of when and how the rules should be broken is prone to deferment. It is a rite of passage for every beginning student of harmony and counterpoint to submit an exercise and receive it back with the parallels circled in red (and points deducted accordingly), to perhaps question the sensibility or fairness of this demerit, but to eventually realize that if he or she wants to pass the class it will be necessary to get good – very good – at identifying and avoiding parallel perfect consonances. The detection of parallel octaves could be called an industry within the larger field of music theory instruction.

The problem occurs when contrapuntal independence is the composer’s goal, which is to say that the parts are not supposed to be heard as doubling each other, and yet they seem to be doing just that, crossing the chasm from polyphony to monophony and leaving the number of voices – even if for just a moment – indeterminate. Of course, parallel octaves occur when instruments or voices explicitly double each other, but in that context the listener is not meant to hear separate melodies: the composer has assigned the same line to multiple players to achieve a certain sonority, not to suggest polyphony. They create the impression that two simultaneous melodic lines – entities which should be perceived as separate at all times – have become indistinguishable, temporarily fusing into one. Parallel octaves are forbidden in traditional counterpoint because – so the textbook explanation goes – they destroy the independence of voices.

Octave parallel