Didascalicon, Book II: the sciences, their parts and their discipline
Chapter XIII. On the threefold music
There are three kinds of music: mundane, human and instrumental. Of the mundane, one is in the elements, another in the planets, another in the seasons. Of that in the elements, one is in number, one in weight, one in measure. Of that in the planets, one is in position, one in motion, one in nature. Of that in the seasons, one is in days, in the alternation of light and night; another in months, in the waxings and wanings of the moon; another in years, in the change of spring, summer, autumn and winter. Of human music, one is in the body, one in the soul, one in the union of both. Of that in the body, one is in growth, according to which it increases, which is common to all things that are born. Another is in the humors, from whose complexion the human body subsists. Which is common to sensible creatures; another in operations, which specially suits the rational, over which the mechanical presides; these, if they do not exceed measure, are good, so that desire is not nourished from them, and weakness ought to be sustained by them, as Lucan relates in praise of Cato.
To him it was a feast to have conquered hunger, to have kept off the bitter winter with a roof, and to have drawn over his limbs a precious garment, the toga after the Roman citizen’s fashion, etc. (Lucan, book II, v. and following.)
Music in the soul: one kind is in the virtues, as justice, piety and temperance; another in the powers, as reason, anger and concupiscence. Music between body and soul is that natural friendship by which the soul is bound to the body not by corporeal bonds but by certain affections, to move and give sense to the body itself; according to this friendship no man ever hated his own flesh. This is music: that the flesh be loved; but more, that the body be cherished while virtue is not destroyed.
Instrumental music: one kind is in striking, as in drums and strings; another in blowing, as in pipes and organs; another in the voice, as in poems and songs. There are also three kinds of musicians: one that composes the song, another that performs with instruments, a third that judges the instrument, the work and the song.