Heptachord

What it means

A heptachord, Greek for “seven-stringed,” is a seven-step diatonic series of notes as represented by today's major scale: seven different notes within an octave, without the repeated eighth note. The term means both the series itself and, historically, a seven-string instrument.

Musical use

In ancient Greek music the lyre often had seven strings, which formed a heptachord. Later, medieval theorists arranged the notes into hexachords, that is, six-note series that could be combined into a larger system. The heptachord, by contrast, describes the seven-note series from which major, minor, and the church modes can be derived: each forms a different section of the seven-step order.

The heptachord should be distinguished from the hexachord with six notes, the pentachord with five, and the octachord, which comprises eight notes and includes the octave. It differs from the pentatonic scale with five degrees through its greater number of degrees and the semitone steps.

Performance practice

Sing or play the seven degrees of a major scale and name them with note names or solmization syllables to hear the series as a whole. Watch the semitones between the third and fourth and between the seventh and eighth degrees, which determine the character of the series.