Tetrachord

In musical theory, a tetrachord is a series of four diatonic tones encompassing the interval of a perfect fourth. Two similar tetrachords, a tone apart, form the diatonic major scale. Originally tetrachord referred to the four strings (tetra - chord) of Greek lyres of which two, the outside or lowest and highest, were fixed (in a just, 3:4, perfect fourth) and two, the inside or middle strings, were movable.

In musical set theory, a tetrachord is a collection of four pitch classes, often one of the three ordered tetrachords in a tone row or set form. Tetrachords may be used to create derived rows and invariance.

See also

• Monad
• Dyad
• Trichord
• Hexachord

• Greek Esoteric Music Theory: The Elemental Tetrachord