parallel-fifth-rule · pachet2001-harmonization-constraints

First, all treatises on harmony do not contain exactly the same rules. In fact, rules have evolved along with music. However, a set of basic rules are considered valid throughout the evolution of tonal music, and therefore always included, such as the parallel fifth rule illustrated below. Second, these rules are not intended to constitute a fully specified algorithm for composing music. They are mainly specifications of forbidden combinations of notes ... This rule states that between two successive chords there should not be a parallel fifth. More precisely, if there is a fifth interval between any two notes of the first chord, then there should not be also a fifth between the two corresponding notes of the next chord. ... Other similar rules apply to parallel octaves or unison intervals.