diatonos

Diatonos, or diatonic systems, denote a set of scales and tonal practices that use seven distinct pitch classes within an octave and rely on a key signature to organize accidentals. The term derives from the Greek diatonos, meaning through tones.

In practice, the diatonic scale comprises five whole steps and two half steps in a fixed order. The most common examples are the major scale and the natural minor scale, each of which shares the same diatonic pitch collection within a given key. There are seven diatonic modes—Ionian, Dorian, Phrygian, Lydian, Mixolydian, Aeolian, and Locrian—that start on different degrees of the scale, producing distinct melodic and harmonic flavors while retaining the diatonic pitch set.

Diatonic harmony builds triads and seventh chords from the diatonic notes. In a major key, triads on I, IV, and V tend to be major; on II, III, and VI tend to be minor; and the seventh degree yields a diminished chord. This framework underpins much Western tonal music from the Baroque through the common-practice period and beyond, supporting functional relationships among chords, bass movement, and cadence.

Diatonos are distinguished from chromatic or atonal music, which use notes outside the diatonic set. While diatonic systems remain central in many genres, composers frequently borrow or alter tones, creating chromatic harmony, modulation, or non-diatonic scales that extend beyond strict diatonic practice.