Voice leading (or part writing) is the linear progression of individual melodic lines (voices or parts) and their interaction with one another to create harmonies, typically in accordance with the principles of common-practice harmony and counterpoint. Rigorous concern for voice leading is of greatest importance in common-practice music, although jazz and pop music also demonstrate attention to voice leading to varying degrees. In Jazz Theory, Gabriel Sakuma writes that "[a]t the surface level, jazz voice-leading conventions seem more relaxed than they are in common-practice music." Marc Schonbrun also states that while it is untrue that "popular music has no voice leading in it, [...] the largest amount of popular music is simply conceived with chords as blocks of information, and melodies are layered on top of the chords." Example The score below shows the first four measures of the C-major prelude from J.S. Bach's The Well-Tempered Clavier, Book 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 four block chords (with two inverted): I – II – V – I. In (c), the four measures are presented as five horizontal voices identified by the direction of the stems (which are added even though the notes are actually whole notes). Notice that each voice consists of just 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 the voices do not move at the same time. History Voice leading developed as an independent concept when Heinrich Schenker stressed its importance in "free counterpoint", as opposed to strict counterpoint. He wrote: 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.) Common-practice conventions and pedagogy Chord connection Western musicians have tended to teach voice leading by focusing on connecting adjacent harmonies because that skill is foundational to meeting larger, structural objectives. Common-practice conventions dictate that melodic lines should be smooth and independent. To be smooth, they should be primarily conjunct (stepwise), avoid leaps that are difficult