A motive is a very short musical idea (melodic, rhythmic, or both), on which an entire movement or section is based. The motive usually recurs throughout the piece in a rich variety of forms, and unifies the piece. A musical theme consists of a series of motives.
Every composer has a characteristic way of dividing his themes into the motives which he develops. In the Classical period, most "Development" sections were based on motives which the composer derived from the various themes he introduced in the "Exposition" section.
