Voice leading refers to the way you move from one chord to another in four-part writing.
My outline will basically cover two lists from the textbook – on pp. 142 – 145, and p. 147.
The textbook refers to the first list as the “nine basic rules of voice leading,” but the first is really a guideline. However, it is a really important guideline, so I’m going to say it more than once:
Keep common tones in the same voice, and move other voices to the nearest chord tones.
Part writing will go so much more smoothly if you follow this basic principle than if you ignore it.
The Nine Eight Basic Rules of Voice Leading
- General Principle: keep common tones in the same voice, and move other voices to the nearest chord tones, as long as this does not create other voice leading errors. For example, moving from a C major triad (C – E – G) to an F major triad (F – A – C) involves one common tone between the two triads — C. If the C major triad is in root position, then there will be two C’s in the first triad (one in the bass, and one in some other voice). The bass will probably move to the root of the F major triad, but the other C can remain in its voice and repeat itself in the F major triad. The most common errors that could result are objectionable perfect parallel intervals, but you could also end up with doubling issues or missing chord tones. Remember that this is a guideline, not a rule, but that it is a great way to start the process.
- Leaps: stepwise motion is preferred. Avoid large leaps (greater than a P4 or P5) in upper voices, which is like our counterpoint rules. The bass can leap often by 4/5 or even 8, as it has to move more to support the changing harmonies.
- Augmented and diminished intervals: avoid augmented intervals. Diminished intervals usually descend, and usually occur in the bass.
- Contrapuntal motion: motion types are the same as two voice counterpoint. Avoid having all the voices move in similar motion.
- Forbidden parallels (P5/8): forbidden in the same way as in species counterpoint. Consecutive perfect intervals by contrary motion are also not allowed. Consecutive perfect intervals can only happen if they are unequal (one diminished) and not in outer voices.
- Direct/Hidden 5ths/8ves: occur when voices move in similar motion, with a leap in the soprano. This is also similar to species counterpoint.
- Leading Tone: resolve the LT up by step to tonic, especially in outer voices. Sometimes the leading tone can be frustrated if voice above LT moves to tonic. A frustrated LT drops to the dominant scale degree.
- Voice overlap and crossing: forbidden the same ways as in species counterpoint.
- The unison rule is really a subset of overlapping and crossing. You can have a unison between two voices as long as it is approached and left by contrary motion. Otherwise, you’ll have voice crossings or overlaps.
Changes of Voicing or Position
A repeated chord can its voicing change between chords. If the bass remains the same you can move either two or three of the upper voices.
If a chord changes position (from root to first inversion, for example), then one of the upper voices must remain static.
Some How-To Guidelines for Basic Types of Progression
Root movement by fifth: The smoothest voice leading occurs when the common tone remains in the same voice, and the other two upper voices move by step to the closest chord tones.(I – IV, I – V, V – I, vi – ii, ii – V, etc.)
Root movement by third: Triads with roots a third apart will have two common tones between them. Keep both common tones in the same voice, with the remaining voice moving by step. (I – vi, vi – IV, etc.)
Root movement by second: Chords a second apart will not have any common tones. These types of progression are the most susceptible to illegal parallel intervals, since the nearest chord tones are all the same distance away in the same direction. The safest voice leading involves moving all the upper voices in contrary motion to the bass.