[Now then, there being three species into which all
harmony is divided, equal in the magnitude of systems or
intervals and force of notes and tetrachords, we find that
the ancients never disputed about any more than one; for
they never troubled themselves with the chromatic or diatonic, but differed only about the enharmonic; and there
no farther than about the great interval called the diapason.
The further subdivision indeed caused some little variance,
but they nearly all agreed that harmony itself is but one.1
Therefore he must never think to be a true artist in the understanding and practice of music, who advances no farther
than the single knowledge of this or that particular: but
it behooves him to trace through all the particular members
of it, and so to be master of the whole body, by understanding how to mix and join all the divided members.
For he that understands only harmony is confined to a
single manner. Wherefore, in short, it is requisite that
the sense and understanding concur in judging the parts of
music; and that they should neither be too hasty, like
those senses which are rash and forward, nor too slow, like
those which are dull and heavy; though it may happen
sometimes, through the inequality of Nature, that the same
senses may be too slow and too quick at the same time.
Which things are to be avoided by a sense and judgment
that would run an equal course.