The second division of the sonata-allegro form is devoted to a more or less extensive and elaborate manipulation and combination of such figures, motives, phrases or Parts of the Exposition as prove inviting and convenient for the purpose, or challenge the imaginative faculty of the composer.

In this division, opportunity is provided for the exhibition of technical skill, imagination and emotional passion; for the creation of ingenious contrasts and climaxes, and, in a word, for the development of unexpected resources not strikingly manifest in the more sober presentation of the thematic factors during the Exposition.

The intermingling of _new material_ is naturally also involved in the process of development; sometimes to such an extent that the new predominates over the old,--in which case the middle Division is more properly called an EPISODE.
This second Division of the sonata-allegro form (the Development or Episode) corresponds precisely, as will be recognized, to the second Part of the Three-Part Song-form; consequently, it represents the "departure" (see page 90), and entails, in rational form, the significant "return" to the beginning.

Further, it matches to some degree the "digression" in the rondo-forms.

At all events, its important structural function is to establish contrast; and the necessity for corroboration of the leading thematic ideas--in consequence of this contrast--is satisfied in the Division which succeeds.
It is sometimes possible to mark the exact point where the Development ends and the process of re-transition commences; but usually the return to the beginning is accomplished so gradually that no sensible interruption occurs.
THE RECAPITULATION .-- This, the third Division, is, as usual, a review of the original presentation of the thematic material,--the recurrence of the Exposition.