An Intensive Journey to Demystifying the Fretboard - Part 5

If you haven’t read yet, make sure to check the previous segment of the series:
Part 4 - Learning the Open Triads

Voice leading is the linear movement of individual melodic lines or parts, their interaction leads to expressed harmonies. In other words, voice leading allows us to understand where voices want to go, by considering where they come from and what everybody else around is concurrently doing.

Smoothness and Indepenence

The primary interest in voice leading is to maximise smoothness and promote the independence of voices. These virtues of part-writing are satisfied when the voices move as little as possible and in different directions.

Considering these goals, we derive the following straight forward rules:

Common Note Principle; If two chords have a note in common, try to keep it in the same voice.
Contrary Motion; If not or for some reason you don’t want to keep it there, make sure that some of the voices move in different directions.
Make sure that you don’t cross voices - avoiding large jumps helps.

Agustin Barrios' Preludio Saudade from La Catedral is a perfect example of voice leading, by studying just a couple of measures, it completely demonstrates the application of these rules.

La Catedral - Preludio Saudade; Measures 10-11 and 19-20.

Diatonic Progressions

Let's examine the possible diatonic root progressions and their voice-leading options:

Chords that their roots are a fourth or a fifth apart have one common tone. Try to keep it in the same voice but if you don’t want, make sure that some of the voices move in different directions.
Chords that their roots are a third or a sixth apart have two tones in common. You can keep one or both at the same voices, or make voices move in opposite directions.
Chords with roots a second or seventh apart don’t have any notes in common, so your only option is to move all voices in different directions.

These rules are mere guidelines and should never obstruct musical expression. Most great composers historically operate on the frontier of what is considered acceptable at any given time. It is the responsibility of the thoughtful composer though to understand, internalise and analyse the voice leading principles in part-writing in addition to important musical works.

Play and listen carefuly the following voice leading example, analyse the linear movement of the voices. Finaly, apply these simple rules to other progressions.

Voice Leading Example in a Diatonic Progression

Parallel Movement in Instrumental Writing

Parallel movement is generally avoided as it takes away the individuality of the voices, but in instrumental writing, it can be an effective device for underlining a melody with a greater sense of cohesiveness and density. Claude Debussy and Maurice Ravel, architects of the contemporary music, used parallel melodic harmonies extensively; but there are examples of parallel movement even in Bach.

In a contrapuntal context, parallel harmonies may provide contrast but should be only used sparingly.