Etymologiae, Book III, chapters 16-19: De inventoribus eius to De triformi musicae divisione
Chapter XVI. On its inventors Moses says that the discoverer of the art of music was Tubal, who was of the stock of Cain before the flood. The Greeks say that Pythagoras found the first beginnings of this art from the sound of hammers and the stretching of struck strings. Others say that Linus of Thebes and Zetus and Amphion were first renowned in the art of music. After them this discipline was gradually directed especially and increased in many ways, and it was as shameful not to know Music as letters. It was interposed not only in sacred rites but in all solemn occasions, and in all matters glad or sadder. For as in divine worship hymns, so at weddings Hymenaeals, and at funerals threnodies, and lamentations were sung to pipes. At banquets a lyre or cithara was carried round, and for each reclining guest a banquet kind of songs was arranged.
Chapter XVII. What music can do Therefore without Music no discipline can be perfect, for there is nothing without it. For the world itself is said to be composed by a certain harmony of sounds, and the heaven itself to be turned about under the modulation of harmony. Music moves the affections and provokes the senses to a different state. In battles also the concord of the trumpet kindles the fighters, and the more vehement the blare, the braver becomes the spirit for the contest. Song also exhorts the rowers; music soothes the mind to bear labours, and the modulation of the voice consoles the weariness of single works. Music also calms excited minds, as it is read of David, who by the art of modulation delivered Saul from the unclean spirit. Music even draws beasts, and serpents also, birds and dolphins, to hear its modulation. But whatever we speak, or are moved inwardly by the pulses of the veins, is proved to be joined by musical rhythms to the powers of harmony.
Chapter XVIII. On the three parts of music The parts of music are three: harmonic, rhythmic, metric. The harmonic is that which distinguishes in sounds the high and the low.
The rhythmic is that which inquires into the running of the words, whether the sound coheres well or ill. The metric is that which knows by probable reason the measure of the different metres, as for example the heroic, the iambic, the elegiac, and the rest.
Chapter XIX. On the threefold division of music For every sound, which is the material of songs, it is agreed that the nature is threefold. The first is harmonic, which consists of songs of voices. The second organic, which consists of breath. The third rhythmic, which receives numbers by the beat of the fingers. For sound is produced either by the voice, as through the throat; or by breath, as through a trumpet or pipe; or by a beat, as through a cithara, or through anything else that is melodious by striking.