The object of the transition is, as usual, _to lead into the new key_ (of the Subordinate theme).

It is sometimes, though very rarely, omitted.
The Subordinate theme contrasts notably with its fellow, but asserts equal importance, as a rule, and may be of equal, or nearly equal, length.

The addition of a codetta is almost indispensable, and frequently two or more appear, growing successively shorter, and generally repeated.

In the sonata-allegro _the Exposition closes, as a rule, with a very decisive perfect cadence_, followed by a double-bar, and--especially in older sonatas--repetition-marks; the repetition of the Exposition being justly considered important, as a means of emphasizing the "statement," and enforcing the hearer's attention to the thematic contents before preceding to their development in the second division of the form.

In the sonatine-form, on the contrary, this positive termination of the Exposition (and consequently the double-bar and repetition) will very rarely be found.
THE DEVELOPMENT, OR MIDDLE DIVISION.