An important principle of musical construction. The use of repetition achieves tonal stability and thematic unity. In contrapuntal music, four devices of repetition are used: Ostinato: repetition in the same part at the same pitch; Sequence: repetition in the same part at a different pitch; Stimmtausch: repetition in a different part at the same pitch; Imitation: repetition in a different part at a different pitch.