The conception of sonata form as expounded by Charles Rosen has provedenormously useful for understanding music of the later eighteenth andnineteenth centuries. In this view, a sonata movement is a dramatization offundamental tonal and motivic processes; to analyze sonata form is touncover the expressive aspirations of a composer, even of an age. Neither asingle formal structure nor a simple principle or device, Classical sonataform is central to the personal styles of Haydn, Mozart, and Beethoven.Hence it is almost a contradiction in terms to speak of the same form inmusic of other composers, particularly an earlier one such as Bach, whosepreludes and fugues are in some ways the antithesis of a Classical sonatamovement.

Still, many commentators have found elements of sonata form in Bach’smusic. Ten preludes in Book 2 of The Well-Tempered Clavier(WTC2) contain a central double bar; in some of thesepreludes the second half incorporates a distinct recapitulation section. Bythe time Bach completed WTC2 around 1740, sonata form wasbeing employed routinely by younger composers, including his son CarlPhilipp Emanuel. But Sebastian’s preludes differ from mostcontemporary sonata movements in their contrapuntal texture and theiravoidance of verbatim recapitulation; his fugues bear even fewer outwardresemblances to Classical sonata form, not least in their through-composeddesigns and elided phrasing. Yet even Bach’s fugues may dramatize atonal design—modulation away from and back to the tonic, articulatedby thematic entries—in ways that anticipate Classical sonatamovements. How substantial are those features shared with Classical sonataform, and what expressive aspirations might they embody?

Among the features not shared is a consistent division intoexposition, development, and recapitulation sections, and the subdivision ofthe exposition and recapitulation into first and second thematic or tonalareas. Even the D-Major Prelude of WTC2 , the mostsonatalike movement in the WTC , lacks a distinctlyarticulated second theme.” The passage after the double bar, althoughmodulating more remotely than the outer divisions, is not so different fromthe latter that it could be called a development.