binary form

two part form; AB

The form of a piece which falls into two sections: the first begins in the tonic and finishes with a cadence either in the tonic (closed binary), or in the dominant (open binary); the second section starts in the new key (usually dominant), modulates and works back to the tonic. Each section is repeated. The main principle is the contrast of key. If the opening material is repeated (often with modifications) towards the end of the second section, it is called rounded binary form. Unsuitable for long pieces and the usual form for Baroque dance movements (allemande, sarabande, courante, gigue, gavotte, bourre, minuets etc).