And yet, with this coherence, there
must always be stimulating and refreshing variety; for a too constant
insistence on the main material produces intolerable monotony, such as
the "damnable iteration" of a mediocre prose work or the harping away
on one theme by the hack composer. In no art more than music is this
dual standard of greater importance, and in no art more difficult to
attain. For the raw material of music, fleeting rhythms and waves of
sound, is in its very nature most incoherent. Here we are not dealing
with the concrete, tangible and definite material which is available
for all the other arts, but with something intangible and elusive. We
know from the historical record[9] of musical development, that, only
after centuries of experimentation conducted by some of the best
intellects in Europe, was sufficient coherence gained so that there
could be composed music which would compare with the simplest modern
hymn-tune or part-song. And this was long after each of the other
arts--architecture, sculpture, painting and literature--had reached
points of attainment which, in many respects, have never since been
equalled.

[Footnote 9: Compare Parry's _Evolution of the Art of Music_, passim
and D.G. Mason's _Beethoven and his Forerunners_, Chapter I.]

Before carrying our inquiries further, something must be said about
the two main lines of musical development which led up to music as we
know it to-day. These tendencies are designated by the terms
_Homophonic_ and _Polyphonic_. By homophonic,[10] from Greek words
signifying a "single voice," is meant music consisting of a _single_
melodic line, as in the whole field of folk-songs (which originally
were always unaccompanied) or in the unison chants of the Greeks and
the Gregorian tones of the early church, in which there is _one
melody_ though many voices may unite in singing it. Later we shall see
what important principles for the growth of instrumental music were
borrowed from the instinctive practise associated with the folk-song
and folk-dance. But history makes clear that the fundamental
principles of musical coherence were worked out in the field of music
known as the _Polyphonic_. By this term, as the derivation implies, is
meant music the fabric of which is made by the interweaving of
_several_ independent melodies. For many centuries the most reliable
instrument was the human voice and the only art-music, _i.e._, music
which was the result of conscious