GENUS, in Music, by the ancients called genus melodie, is a certain manner of dividing and subdividing the principles of melody; that is, the consonant and dissonant intervals, into their concinnous parts.
The moderns considering the octave as the most perfect of intervals, and that whereon all the concords depend, in the present theory of music, the division of that interval is considered as containing the true division of the whole scale.
But the ancients went to work somewhat differently: the diatessaron, or fourth, was the least interval which they admitted as concord; and therefore they sought first how that might be most conveniently divided; from whence they constituted the diapente and diapason.
The diatessaron being thus, as it were, the root and foundation of the scale, what they called the genera, or kinds, arose from its various divisions; and hence they defined the genus modulandi to be the manner of dividing the tetrachord and disposing its four sounds as to succession.
The genera of music were three, the enharmonic, chromatic, and diatonic. The two first were variously subdivided;
Geocentric subdivided; and even the last, though that is commonly reckoned to be without any species, yet different authors have proposed different divisions under that name, without giving any particular names to the species as was done to the other two.
For the characters, &c. of these several genera, see ENHARMONIC, CHROMATIC, and DIATONIC.