chords or harmonies are derived from it more than from the natural minor scale or the melodic minor scale. The augmented second between its sixth degree and its raised seventh degree (the "leading tone"), traditionally considered undesirable in melodic progression, is avoided by placing these pitches in different voices in adjacent chords, as in this progression: F A D, F G B, F A C (ii°b–V7d–iv in C minor). The A in the middle voice does not ascend to B, and the B in the upper voice does not descend to A. Heptatonia prima and secunda The names heptatonia prima and heptatonia secunda apply to seven-note scales that can be formed using five tones (t) and two semi-tones (s), (also called whole-steps and half-steps), but without two semi-tones in succession. Throughout history and to the present day, some have occurred much more commonly than others, namely Ionian (also called the major scale), Aeolian (also called the natural minor scale), melodic ascending minor, Dorian, Mixolydian, Lydian, Lydian dominant, the major-minor, and altered scales. Heptatonia prima In these scales the semi-tones are maximally separated. They are known most commonly as the diatonic modes. Beginning on keynote C and working up the notes of the 'natural minor' scale (A, B, C, D, E, F, G, A), the seven modes are: Aeolian mode (natural minor) t-s-t-t-s-t-t Locrian mode s-t-t-s-t-t-t Ionian mode (major) t-t-s-t-t-t-s Dorian mode t-s-t-t-t-s-t Phrygian mode s-t-t-t-s-t-t Lydian mode t-t-t-s-t-t-s Mixolydian mode t-t-s-t-t-s-t Heptatonia secunda While the diatonic modes have two and three tones on either side of each semitone, the heptatonia secunda modes have one and four. These are sometimes called modes of the melodic ascending minor since that is the most commonly used scale of this type, but other modes can be produced by starting on the different scale notes in turn. Thus starting on keynote A as above and following the notes of the ascending melodic minor (A, B, C, D, E, F, G) yields these seven modes: 'Melodic ascending minor' t-s-t-t-t-t-s 'Phrygian raised sixth' s-t-t-t-t-s-t combines the Phrygian flat second and Dorian raised sixth 'Lydian raised fifth' t-t-t-t-s-t-s combines the Lydian fourth with a raised fifth 'Acoustic' or 'Lydian Dominant' Scale t-t-t-s-t-s-t So-called because it is close to the scale built on natural overtones and combines Lydian raised fourth with Mixolydian (Dominant) flat seventh 'Major minor' scale t-t-s-t-s-t-t Like natural minor (aeolian) but with a major third 'Half