Diatonic scale

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Diatonic scale on C. The half steps are E–F (the third to the fourth note) and B–C (the seventh to the recurring first note, often called the eighth note).

In music theory a diatonic scale is a heptatonic (seven-note) scale that includes five whole steps (whole tones) and two half steps (semitones) in each octave, in which the two half steps are separated from each other by either two or three whole steps. In other words, the half steps are maximally separated from each other.

The seven pitches of any diatonic scale can also be obtained by using a chain of six perfect fifths. For instance, the seven natural pitch classes that form the C-major scale can be obtained from a stack of perfect fifths starting from F:

F–C–G–D–A–E–B.

Any sequence of seven successive natural notes, such as C–D–E–F–G–A–B, and any transposition thereof, is a diatonic scale. Modern musical keyboards are designed so that the white-key notes form a diatonic scale, though transpositions of this diatonic scale require one or more black keys. A diatonic scale can be also described as two tetrachords separated by a whole tone. In musical set theory, Allen Forte classifies diatonic scales as set form 7–35.

The term diatonic originally referred to the diatonic genus, one of the three genera of the ancient Greeks, and comes from Ancient Greek: διατονικός, romanized: diatonikós, of uncertain etymology. Most likely, it refers to the intervals being "stretched out" in that tuning, in contrast to the other two genera (chromatic and enharmonic).

This article does not concern alternative seven-note scales such as the harmonic minor or the melodic minor which, although sometimes called "diatonic", do not fulfill the condition of maximal separation of the semitones indicated above.