2The inflexion of the voice is two-fold; first, when it is monotonous, second, when it proceeds by intervals. The first is not limited by cadences at the close, nor in any other place; no perceptible difference of tone being discoverable between its beginning and its ending, the time between each sound is however distinctly marked, as in speaking, when we pronounce the words, sol, lux, flos, nox. Herein the ear does not perceive any difference of tone between the beginning and the ending, by the voice rising higher or descending lower; neither, that from a high pitch it becomes lower, nor the contrary. But when the voice moves by intervals, it is differently inflected, being sometimes at a high pitch, and sometimes at a low one, and resting at different times on different tones; by doing which with quickness and facility, it appears unfixed. Thus in singing, the variety of inflexion produces an air. In short, by the use of different intervals, the tones are so marked and determined, that we perceive the pitch at which it begins, and that at which it finishes, though the intermediate tones are not heard.
2The voice, in its changes of position when shifting pitch, becomes sometimes high, sometimes low, and its movements are of two kinds, in one of which its progress is continuous, in the other by intervals. The continuous voice does not become stationary at the “boundaries” or at any definite place, and so the extremities of its progress are not apparent, but the fact that there are differences of pitch is apparent, as in our ordinary speech in sol, lux, flos, vox; for in these cases we cannot tell at what pitch the voice begins, nor at what pitch it leaves off, but the fact that it becomes low from high and high from low is apparent to the ear. In its progress by intervals the opposite is the case. For here, when the pitch shifts, the voice, by change of position, stations itself on one pitch, then on another, and, as it frequently repeats this alternating process, it appears to the senses to become stationary, as happens in singing when we produce a variation of the mode by changing the pitch of the voice. And so, since it moves by intervals, the points at which it begins and where it leaves off are obviously apparent in the boundaries of the notes, but the intermediate points escape notice and are obscure, owing to the intervals.