Voice leading

Example

The score in the following example reproduces the first four measures of Johann Sebastian Bach's Preludium in C major (BWV 846a) from the 1722 keyboard work Well Tempered Keyboard, volume 1. Letter (a) presents the original score while (b) and (c) present reductions (simplified versions) intended to clarify the harmony and implied voice leading, respectively.

In (b), the same measures are presented as consisting in four block chords: the first and the fourth ones are the same, a triad of C major (I); the second is a minor 7th chord on D (II), inverted to show C in the bass; the third is a dominant 7th on G (V), inverted to show B in the bass.

In (c), the four measures are presented as formed of five horizontal parts (voices) identified by the direction of the stems, each consisting in only three notes: from top to bottom, (1) E F — E; (2) C D — C; (3) G A G —; (4) E D — E; (5) C — B C. The four chords result from the fact that not every voice moves at the same time. To see this, look at the highest note of each chord - E, F, F, and E - this corresponds to 1), the second highest note of each chord is C, D, D, and C - corresponding to 2) etc.

History

Voice leading developed as an independent concept when Heinrich Schenker stressed its importance in "free counterpoint", as opposed to strict counterpoint. He wrote:

All musical technique is derived from two basic ingredients: voice leading and the progression of scale degrees [i.e. of harmonic roots]. Of the two, voice leading is the earlier and the more original element.The theory of voice leading is to be presented here as a discipline unified in itself; that is, I shall show how […] it everywhere maintains its inner unity.

Schenker indeed did not present the rules of voice leading merely as contrapuntal rules, but showed how they are inseparable from the rules of harmony and how they form one of the most essential aspects of musical composition. (See Schenkerian analysis: voice leading).

Chord Connection

Although pacing a piece's various arrivals is the most important result of voice leading, Western musicians have tended to teach voice leading by focusing on connecting adjacent harmonies because that skill is foundational to meeting larger, structural objectives.

On a chord-to-chord level, common-practice conventions dictate that lines should be smooth (by avoiding leaps and retaining common tones) and independent (by avoiding simultaneous movement of all voices in the same direction and parallel perfect intervals). Contrapuntal conventions likewise consider permitted or forbidden melodic intervals in individual parts, intervals between parts, the direction of the movement of the voices with respect to each other, etc. (See Counterpoint for more details on rules, especially in species counterpoint; see also Contrapuntal motion.) Whether dealing with counterpoint or harmony, these conventions emerge not only from a desire to create easy-to-sing parts but also from the constraints of tonal materials and from the objectives behind writing certain textures. In other words, the practical, technical, and aesthetic considerations surrounding voice leading reinforce one another.

Move each voice the shortest distance possible. One of the main conventions of common-practice part-writing is that, between successive harmonies, voices should avoid leaps and retain common tones as much as possible. This principle was commonly discussed among 17th- and 18th-century musicians as a rule of thumb. For example, Rameau taught "one cannot pass from one note to another but by that which is closest." In the 19th century, as music pedagogy became a more theoretical discipline in some parts of Europe, the 18th-century rule of thumb became codified into a more strict definition. Johann August Dürrneberger coined the term "rule of the shortest way" for it and delineated that:

1. When a chord contains one or more notes that will be reused in the chords immediately following, then these notes should remain, that is retained in the respective parts.
2. The parts which do not remain, follow the law of the shortest way (Gesetze des nächsten Weges), that is that each such part names the note of the following chord closest to itself if no forbidden succession arises from this.
3. If no note at all is present in a chord which can be reused in the chord immediately following, one must apply contrary motion according to the law of the shortest way, that is, if the root progresses upwards, the accompanying parts must move downwards, or inversely, if the root progresses downwards, the other parts move upwards and, in both cases, to the note of the following chord closest to them.

This rule was taught by Bruckner to Schoenberg and Schenker, who both had followed his classes in Vienna. Schenker re-conceived the principle as the "rule of melodic fluency":Schenker attributed the rule to Cherubini, but this is the result of a somewhat inexact German translation. Cherubini only said that conjunct movement should be preferred. Franz Stoepel, the German translator, used the expression Fließender Gesang to translate mouvement conjoint. The concept of Fließender Gesang is a common concept of German counterpoint theory. Modern Schenkerians made the concept of "melodic fluency" an important one in their teaching of voice leading.

Move the soprano and bass in contrary or oblique motion if possible. Common-practice composers preferred contrary and oblique motion as it promoted voice independence.

Voice crossing should be avoided unless to create melodic interest.

Avoid parallel perfect intervals such as parallel unisons, parallel 5ths and parallel octaves between any two voices to promote voice independence.

Harmonic roles

As the Renaissance gave way to the Baroque era in the 1600s, part writing reflected the increasing stratification of harmonic roles. This differentiation between outer and inner voices was an outgrowth of both tonality and homophony. In this new Baroque style, the outer voices took a commanding role in determining the flow of the music and tended to move more often by leaps. Inner voices tended to move stepwise or repeat common tones.

A Schenkerian analysis perspective on these roles shifts the discussion somewhat from "outer and inner voices" to "upper and bass voices." Although the outer voices still play the dominant, form-defining role in this view, the leading soprano voice is often seen as a composite line that draws on the voice leadings in each of the upper voices of the imaginary continuo. Approaching harmony from a non-Schenkerian perspective, Dmitri Tymoczko nonetheless also demonstrates such "3+1" voice leading as a feature of tonal writing.

Conventions in the 19th century and beyond

Much music that doesn't follow common-practice part-writing conventions nonetheless often follows larger voice leading principles. For instance, Debussy's "Nocturnes" from the 19th century and Morton Feldman's "The Viola in My Life" (pieces as different from each other as they are distinct from common-practice era music) both derive their formal connections from soprano voice leading.

In this sense, the idea of "part-writing rules" can be somewhat misleading. Wise pedagogues understand that such rules aren't there to be "broken," but to help students hone their perception and develop judgment about the larger principles.

Neo-Riemannian theory examines another facet of this principle. That theory decomposes movements from one chord to another into one or several "parsimonious movements" between pitch classes instead of actual pitches (i.e., neglecting octave shifts). Such analysis shows the deeper continuity underneath surface disjunctions, as in the Bach example from BWV 941.