- Alexander Sanchez-Behar
A nine-note scale or collection comprised of the recurring pattern of two semitones and a whole tone: C–C♯–D–E–F–F♯–G♯–A–B♭–C (enharmonic spellings are common). The scale is widely known as enneatonic or nonatonic, yet other labels exist: ‘mode 3’ of limited transposition from Messiaen (1944), the ‘nine-step scale’ from Tcherepnin (1962), and set class 9–12 [01245689T] from Forte (1973).
The enneatonic scale has symmetrical properties, reducing its number of distinct transpositions to four. Analogous to other symmetrical scales such as the octatonic, the intervallic arrangement of this scale can be rotated to begin with a semitone or whole tone. It is possible to generate the enneatonic scale by superimposing other symmetrical collections, using either three augmented triads, two hexatonic scales a semitone apart, or a whole-tone scale combined with a hexatonic scale (ex.1). Conversely, it can be thought of as the complement of an augmented triad. One of the inherent properties of collections based on symmetrical octave partitioning such as enneatonic is the saturation of major or minor thirds. The enneatonic scale contains nine major thirds, the maximum number for all conceivable nine-note scales....