Sonata Theory is an approach to the description of sonata form in terms of individual works' treatment of generic expectations. For example, it is normative for the secondary theme of a minor-mode sonata to be in either the key of III or v. If a composer chooses to break this norm in a given piece, that is a deviation that requires analytical and interpretive explanation. The essentials of the theory are presented by its developers, James Hepokoski and Warren Darcy, in the book ''Elements of Sonata Theory'', which won the Society for Music Theory's Wallace Berry Award in 2008. Although the theory is particularly designed to treat late-eighteenth-century works such as those by Mozart, Haydn, and Beethoven, many of its principles are applicable to works in sonata form from later centuries.
Provided by Wikipedia