Voice-leading in Bach chorales: Parallel fifths and octaves
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What's the problem with parallels?
The reasons why Bach (along with virtually all tonal composers) avoids parallel fifths and octaves are not straightforward. In the end, avoiding the sound of parallels is part of the aesthetic of tonal music - they are considered ugly in the same way as, for example, unprepared dissonances. There is not necessarily a wholly logical reason why this might be, it is just a feature that has to be accepted and absorbed.
The following factors have probably contributed to the emergence of this 'rule' of tonal composition:
- The intervals of a fifth and an octave create a distinctive 'bare' sound. If they are written in parallel attention is drawn to this bareness, even if there are other voices in the texture.
- Early sacred vocal music involved a lot of parallel motion between voices, particularly in fifths and octaves. As music developed, there was an increasing emphasis on writing independent parts - the avoidance of parallel motion (especially fifths and octaves) formed a part of this development.
- Theorists as early as 1300 advised against the use of parallel fifths - although composers continued to write them occasionally, by the end of the Renaissance, they were avoided in virtually all types of Western classical music
- Since at least the 1500s, a large number of composers began their training by learning 'species counterpoint', a method for learning how to write Renaissance polyphony. In species counterpoint compositional exercises, the shape of the lines and the way they interact are very carefully controlled - parallel fifths and octaves are strictly forbidden.
- Parallel fifths imply an ungainly progression of root position triads with all the voices moving together. Avoiding parallel fifths helps to eliminate this type of voice-leading.
The 'ban' on parallel fifths and octaves is therefore bound up with other less easily defined aspects of music - learning how to avoid them also guides your writing in the right direction in terms of both harmonic progressions and part-writing in general.
What exactly is not allowed?
Consecutive parallel consecutive fifths and octaves
You must not write fifths or octaves that are both:
consecutive (i.e. in two chords that are next to each other)
and parallel (i.e. moving in the same direction)
In the example below, A is not allowed, but in B the fifths are not consecutive, and in C they are not moving in parallel (this is the end of one phrase and the beginning of the next):
Hidden or exposed fifths and octaves
The sensitivity to parallels in the simple texture of Bach's chorale style means that even similar motion to a fifth or octave can give the impression of parallels. The example below explains these 'hidden' or 'exposed' octaves - the same can happen with fifths.
The rule is that you should also avoid similar motion to an octave or a fifth between the outer parts (soprano and bass) when (and only when) the soprano is also leaping. This is because the the leap to a perfect interval with the bass stand out and sound a bit like parallels. You may well not hear this yourself, but you just have to accept that it is part of the convention of writing in this style. In the example below, the second progression is OK because the soprano moves by step and the third progression is OK because the outer voices are in contrary motion.
Where do they crop up and how can they be avoided?
The only way to avoid parallels is to check religiously at all stages as outlined in my Bach chorale method. If you write a bass line first that avoids parallels, you are much less likely to end up with them in the inner parts. To can save time checking by following these steps:
For each chord progression, make the following checks
- are any parts moving in the same direction? - if not, stop checking, there cannot be parallels
- if any parts are moving in the same direction, are they moving by the same interval? - again, if not, stop checking
- finally, check what the interval is between the parts (thirds, fourths and sixths are fine)
There are a few specific circumstances in which fifths and/or octaves are particularly likely to crop up:
- two chords in which both the harmony and melody are moving in the same direction by step (as in example A below)
- two chords in which all the parts are moving in the same direction
- adding a passing note in the progression Ib-V (as in example B below)
- adding a passing seventh at the same time as an anticipation (as in example C below)