But similarity of style is by no means obligatory, the element of contrast having become more important than Unity, in a design of such extent.

It is also usually complete in itself, though its connection with its principal song may involve a few measures of transitional material.
THE "DA CAPO."-- This association of song-forms is subject to the principle which governs all tripartite forms, namely, the return to the beginning, and confirmation of the first (or principal) statement; not only because of the general desirability of such a return, but because _the necessity for it increases with the growth of the form_.

In a design that comprises a number of entire song-forms, it may be regarded as indispensable.
Therefore, the subordinate song is followed by a recurrence of the principal song,--called the _da capo_ (or "from the beginning"), because of those Italian words of direction given to the player upon reaching the end of the "Trio," or subordinate song.

The reproduction of the principal division is likely to be literal, so that the simple directions "_da capo_" suffice, instead of re-writing the entire division.

But, here again, changes may be made,--generally unimportant variations which do not obscure the form; or an abbreviation, or even slight extension.