Heptatonic scale

A heptatonic scale is a musical scale that has seven pitches, or tones, per octave. Examples include:

• the diatonic scale; including the major scale and its modes (notably the natural minor scale, or Aeolian mode)
• the melodic minor scale, like the Aeolian mode but with raised 6th and 7th ascending
• the harmonic minor scale, like the Aeolian mode but with raised 7th
• the harmonic major scale, like the major scale but with lowered 6th

Indian classical theory postulates seventy-two seven-tone scale types, collectively called melakarta or thaat, whereas others postulate twelve or ten (depending on the theorist) seven-tone scale types.

Several heptatonic scales in Western, Roman, Spanish, Hungarian, and Greek music can be analyzed as juxtapositions of tetrachords. All heptatonic scales have all intervals present in their interval vector analysis, and thus all heptatonic scales are both hemitonic and tritonic. There is a special affinity for heptatonic scales in the Western key signature system.