☞ The same general structure prevails in symphonies, instrumental trios, quartets, etc., and even in classical concertos. The sonata form, distinctively, characterizes the quick opening movement, which may have a short, slow introduction; the second, or slow, movement is either in the song or variation form; third comes the playful minuet or the more modern scherzo; then the quick finale in the rondo form. But both form and order are sometimes exceptional.