26, last movement.
In musical composition this process is known as thematic development, and it generally extends over the whole, or a greater part, of the piece.
Its operation on a smaller scale, with more limited reference to one phrase alone, effects the development of the phrase _by extension_.
The process of extension or expansion, by means of which the phrase usually assumes a somewhat irregular length, consists mainly in the varied repetition of the figures or motives that it contains; and the continuity of the whole, as extension of the _one phrase_, is maintained by suppressing the cadence--suspending all cadential interruption--during the lengthening process.

For example: [Illustration: Example 39.

Fragment of Mendelssohn.] These six measures result from a repetition (variated) of the third and fourth measures of the original--regular--four-measure phrase.

A cadence is due in the fourth measure, but it is not permitted to assert itself; and if it did, its cadential force would be neutralized by the entirely obvious return to (repetition of) the motive just heard.

Further:-- [Illustration: Example 40.