Pseudo-Plutarch, De musica
Goodwin, Ed.

This will be apparent, if any one shall examine every one of the parts, and see what is the subject of their several contemplations. For harmony takes cognizance of intervals, systems, classes of harmonious sounds, notes, tones, and systematical transmutations. Farther than this it goes not. And therefore it would be in vain to enquire of harmony, whether the poet have rightly and (so to speak) musically chosen the Dorian for the beginning, the mixed Lydian and Dorian for the end, or the Hypophrygian and Phrygian for the middle. For the industry of harmony reaches not to these, and it is defective in many other things, as not understanding the force and extent of elegant aptness and proper concinnity. Neither did ever the chromatic [p. 127] or enharmonic species arrive to such force of aptitude as to discover the nature and genius of the poem; for that is the work of the poet. It is as plain, that the sound of the system is different from the sound of the descant sung in the same system; which, however, does not belong to the consideration of harmonical studies. There is the same to be said concerning rhythms, for no rhythm can claim to itself the force of perfect aptitude. For we call a thing apt and proper when we consider the nature of it. The reason of this, we say, is either a certain plain and mixed composure, or both; like the enharmonic species of Olympus, by him set in the Phrygian mood and mixed with the paeon epibatos, which rendered the beginning of the key naturally elegant in what is called the nome of Minerva. For having made choice of his key and measure, he only changed the paeon epibatos for the trochee, which produced his enharmonic species. However, the enharmonic species and Phrygian tone remaining together with the whole system, the elegancy of the character was greatly altered. For that which was called harmony in the nome of Minerva was quite another thing from that in the introduction. He then that has both judgment as well as skill is to be accounted the most accurate musician. For he that understands the Dorian mood, not being able withal to discern by his judgment what is proper to it and when it is fit to be made use of, shall never know what he does; nay, he shall quite mistake the nature and custom of the key. Indeed it is much questioned among the Dorians themselves, whether the enharmonic composers be competent judges of the Dorian songs. The same is to be said concerning the knowledge of rhythm. For he that understands a paeon may not understand the proper use of it, though he know the measure of which it consists. Because it is much doubted among those that make use of paeons, whether the bare knowledge make a man capable to determine [p. 128] concerning the proper use of those rhythms; or, as others say, whether it aspire to presume so far. Therefore it behooves that person to have two sorts of knowledge, who will undertake to judge of what is proper and what improper; first, of the custom and manner of elegancy for which such a composition was intended, and next of those things of which the composition consists. And thus, that neither the bare knowledge of harmony, nor of rhythm, nor of any other things that singly by themselves are but a part of the whole body of music, is sufficient to judge and determine either of the one or the other, what has been already said may suffice to prove.