Trichord

In music theory, a trichord () is a group of three different pitch classes found within a larger group. A trichord is a contiguous three-note set from a musical scale or a twelve-tone row.

In musical set theory there are twelve trichords given inversional equivalency, and, without inversional equivalency, nineteen trichords. These are numbered 1–12, with symmetrical trichords being unlettered and with uninverted and inverted nonsymmetrical trichords lettered A or B, respectively. They are often listed in prime form, but may exist in different voicings; different inversions at different transpositions. For example, the major chord, 3-11B (prime form: [0,4,7]), is an inversion of the minor chord, 3-11A (prime form: [0,3,7]). 3-5A and B are the Viennese trichord (prime forms: [0,1,6] and [0,5,6]).

Historical Russian definition

In late-19th to early 20th-century Russian musicology, the term trichord (трихорд (/trixоrd/)) meant something more specific: a set of three pitches, each at least a tone apart but all within the range of a fourth or fifth.

The possible trichords on C would then be:

Several of these pitch sets interlocking could form a larger set such as a pentatonic scale (such as C–D–F–G–B♭–C'). It was first coined by theorist Pyotr Sokalsky in his 1888 book Русская народная музыка ("Russian Folk Music") to explain the observed traits of the rural Russian folk music (especially from southern regions) that was just beginning to be recorded and published at this time.