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:--.