Genus (music) the other hand, also has twelve pitches to the octave, but the semitones are all of the same size. In contrast, the ancient Greek chromatic scale had seven tones to the octave (assuming alternating conjunct and disjunct tetrachords), and had incomposite minor thirds as well as semitones and whole tones. The (Dorian) scale generated from the chromatic genus is composed of two chromatic tetrachords: whereas in modern music theory, a chromatic scale is: The number and nature of the shades of the chromatic genus vary amongst the Greek theorists. The major division is between the Aristoxenians and the Pythagoreans. Aristoxenus
Rule of the octave Rule of the octave The rule of the octave is a way of harmonizing each note of the diatonic scale, reflecting common practice, and has its origin in the practice of thorough bass, or basso continuo. The rule of the octave also formed the cornerstone of the "regole" (rules) of partimento collections. The rule of the octave was first mentioned in the 17th century in treatises for thorough bass written for lute-like instruments. There is normally a different harmonization for ascending and descending bass lines, and, although called a rule, there are several variants with different chords. Different versions for