h divisions depends to
some extent also upon the length of the piece, though chiefly upon the
specific structural idea to be embodied.

A composition that contains two such sections is called a Two-Part (or
bipartite, or binary) form; and one that contains three, a Three-part
(tripartite, or ternary) form.

Such rare exceptions to these structural arrangements as may be
encountered in musical literature, are limited to sentences that, on
one hand, are so brief as to require no radical division; and, on the
other, to compositions of very elaborate dimensions, extending beyond
this structural distinction; and, furthermore, to fantastic pieces in
which the intentional absence of classified formal disposition is
characteristic and essential.

The terms employed to denote this species ("Song-form" or "Part-form")
do not signify that the music is necessarily to be a vocal composition
of that variety known as the "Song"; or that it is to consist of
several voices (for which the appellation "parts" is commonly used).
They indicate simply a certain _grade_,--not a specific variety,--of
form; an intermediate grade between the smallest class (like brief
hymn-tunes, for example), and the largest class (like complete
sonata-movements). An excellent {84} type of this grade of Form is
found in the Songs Without Words of Mendelssohn, the Mazurkas of
Chopin, and works of similar extent.

The word Part (written always with a capital in these lessons) denotes,
then, one of these larger sections. The design of the Part-forms was
so characteristic of the early German _lied_, and is so common in the
_song_ of all eras, that the term "Song-form" seems a peculiarly
appropriate designation, irrespective of the vocal or instrumental
character of the composition.

The student will perceive that it is the smallest class of forms--the
Phrase-forms,--embracing the phrase, period and double-period, to which
the preceding chapters have been devoted. These are the designs which,
as a general rule, _contain only one decisive perfect cadence_, and
that at the end; and which, therefore, though interrupted by
semicadences, _are continuous and coherent_, because the semicadence
merely interrupts, and does not sever, the continuity of the sentence.
(This grade of forms might be called One-Part forms).

THE PARTS.--If we inquire into the means employed, in the larger
Part-forms, to effect the division of the whole into its broader Parts,
we find