a foregoing one answers the
purposes of confirmation and of balance, and is supposed to be so
effectuated as to institute and maintain unity of style, and some
degree of progressive development. But the second Part, in this
bipartite design, does little or nothing more, after all, than thus to
project the musical thought on outward in a straight line (or along
parallel lines) to a conclusion more or less distant from the
starting-point,--from the melodic members which constitute the actual
germ, or the "text" of the entire musical discourse. A very desirable,
not to say vital, condition is therefore {90} lacking, in the Two-Part
forms; namely, the corroboration of this melodic germ by an emphatic
return to the beginning and an unmistakable re-announcement of the
first (leading) phrase or phrases of the composition.

Nothing could be more natural than such corroboration. Any line of
conduct, if pursued without deviation, simply carries its object
farther and farther away from its origin. If, as in the circle, this
line is led back to the starting-point, it describes the most
satisfying and perfect figure; it perfects, by enclosing space.
Whereas, if it goes straight onward, it ultimately loses itself, or
loses, at least, its connection with its beginning and source.

Nowhere is this principle of _Return_ more significant and imperative
than in music, which, because of its intangibility, has need of every
means that may serve to define and illuminate its design; and hence the
superior frequency and perfection of the Three-Part form, _which, in
its Third Part, provides for and executes this Return to the
beginning_. Its superiority and greater adaptability is fully
confirmed in the practice of composition; the number of Three-Part
forms exceeds the Two-Part, in musical literature, to an almost
surprising degree; and it may therefore be regarded as the design
peculiarly adapted to the purposes of ordinary music writing within
average limits.

The three successive divisions of the Three-Part Song-form may then be
characterized as follows:--

PART I.--The statement of the principal idea; the presentation of the
melodic and rhythmic contents of the leading thought, out of which the
whole composition is to be developed. It is generally a period-form,
at least, closing with a firm perfect cadence in the principal key, or
one of its related keys.

PART II.--The departure (more or less emphatic) from this leading