Voice-leading in Bach chorales: Doubling
[back to the Double SLAP]
Chorales are written in four parts, but there are only three notes in a triad. In order for every voice to have a note to sing, you need to double up on one of the notes.
Most of the time you should reinforce the harmony by doubling the root of the chord, but it is sometimes better to double other notes to get better voice-leading as outlined below.
What are the rules?
The basic rules for triads are as follows (in seventh chords you should include all four notes, so there are no doublings):
* You should not double the third in chord V because doubling the leading note of a scale creates problems with voice-leading.
Why do you not always double the root in first inversion?
Doubling the third of a first inversion chord is often the best way of avoiding parallels as in the following example:
Why double the fifth in chord Ic?
Ic is really just a decoration of chord V as shown below – it is often called a cadential six-four because it forms a sixth and a fourth above the bass in the chord before the V of the cadence. The fifth is doubled in Ic, then, because it is really the root of the following V chord that it decorates that is being doubled.
Why does Bach sometimes break these rules?
Sometimes it is difficult to harmonise a melody in a certain way without creating either parallels or awkward intervals. Because it is better to have a 'wrong' doubling than a parallels or awkward intervals, Bach tends to be more flexible with his doublings. In the example below, doubling the third avoids an augmented second in the alto part.
You should probably stick to the basic rules in your own work in case the examiner does not agree that more unusual doublings are necessary.