3.4 The concept of prolongation
These three basic ways in which dissonant notes occur in music all share one notable feature. They make a note or a harmony extend over a longer period of time than just its bare statement. Two notes of a chord may be stretched out by having a passing note placed between them; a single note may move to a neighbour note, and then return; a harmony may be extended by a suspension, such as a before a cadence. In all these cases, we say that the note or chord involved is being ‘prolonged’ by the use of dissonance. The concept of prolongation is absolutely central to voice-leading analysis, especially when we come to consider deeper levels of structure than the foreground.