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(1) The "words" of any vocal composition. (2) The theme or subject.
Tetrachord [from Gr., tetra, chordon]. Four strings; hence, a succession of four sounds.
The tetrachord always consists of two whole tones and one half-tone. These intervals may be arranged in three ways. The oldest arrangement, called the Pythagorean tetrachord, began with the half-tone, thus : - 9:0 It is generally supposed that the original four-string lyre (called the tetrachordon) was tuned to these sounds. The addition of another tetrachord, beginning with the highest note of this one, gives the scale of the heptachord, or seven-string lyre, thus :- 9: bo This is called the scale of conjunct tetrachords, the A being the note common to both. The addition of a note below this scale, thus :- 9: gives the original octave scale of the lyre.
This scale is the normal Greek scale, called the Dorian. It is doubtless the origin of the modern minor scale. The tetrachord known as Hucbald's had the half-tone in the middle, thus: DEFG.
The Hexachord scales (q. v.) were formed from this tetrachord by adding one letter above and one below, thus :- CDEFGA.
In the modern major scale the half-tone lies between the third and fourth letters of the tetrachord, thus: CDEF, and the scale consists of two of these tetrachords separated by a whole one. Terschak, Ad. Composer, flutist; Germany.
B. 1832; d. 1907.
TETRACHORDAL SYSTEM