Diatonic Scale

In music theory, a diatonic scale (from the Greek διατονικός, meaning " through tones", also known as the heptatonic prima) is commonly defined as a seven-note, octave-repeating musical scale comprising five whole steps and two half steps for each octave, in which the two half steps are separated from each other by either two or three whole steps. This pattern ensures that, in a diatonic scale spanning more than one octave, all the half steps are maximally separated from each other (i.e. separated by at least two whole steps). Alternative definitions are sometimes used in the literature, which may either include seven-note scales (such as the harmonic minor and the melodic minor ones) which do not meet the definition given above, or exclude some of the scales which meet it. These alternative definitions are discussed elsewhere.

The definition given above implies that the seven pitches of any diatonic scale can be obtained using a chain of six perfect fifths. For instance, the seven natural pitches which form the C-major scale can be obtained from a stack of perfect fifths starting from F:

F—C—G—D—A—E—B

This property of the diatonic scales was historically relevant and possibly contributed to their world-wide diffusion because for centuries it allowed musicians to tune musical instruments easily by ear (see Pythagorean tuning).

Any sequence of seven successive natural notes, such as C-D-E-F-G-A-B, and any transposition thereof, is a diatonic scale. Piano keyboards are designed to play natural notes, and hence diatonic scales, with their white keys. A diatonic scale can be also described as two tetrachords separated by a whole tone.

The term diatonic originally referred to the diatonic genus, one of the three genera of the ancient Greeks. In musical set theory, Allen Forte classifies diatonic scales as set form 7-35.