Rosen's book, now in a revised edition, is a follow-up to his classic "Classical Style," and it helps to be acquainted with the earlier work, or at least to be somewhat accustomed to the author's elaborate and occasionally repetitive prose and his habit of illustrating the discussion with copious, lengthy musical examples. The early chapters explain the author's choice of the plural for the title and distinguish his view of the sonata structure as opposed to the single form dictated by nineteenth-century authorities such as Czerny. Particularly interesting, if not altogether coherent, is the attempt to relate the rise of use of sonata principles by composers to the rise in prestige of instrumental music. A couple of chapters on sonata-form predecessors (aria, concerto, other works by early Italians such as Scarlatti and Sammartini) are succeeded by generally lucid discussions on motivic development and the component parts of fully developed sonata form: exposition, development, recapitulation, and coda. The last part of the book examines how sonata structure has continued to influence and at times frustrate post-Classical composers.
If one looks for it, there are brilliant analyses to be found throughout this book, often in unexpected places: a full-scale and fascinating dissection of the first movement of Mozart's great "Prague" Symphony in D major is hidden away in the middle of the "Motif and Function" chapter. Therein lies the major problem of this book for me, in that Rosen, ironically enough in a work about form, seems to have trouble ordering and presenting his ideas in a logical fashion. The chapter on concertos seems intended to illustrate pre-sonata principles, but contradicts its purpose with illustrations mainly from Mozart and his contemporaries. Elsewhere, Rosen first cites minuet form as a sonata-form predecessor but then clouds the issue by discussing classical minuets in a later chapter--the casual reader may miss the distinction, which he never states explicitly. In fact, some important overall points--that the turn toward the subdominant in many recapitulations is intended to balance the basic tonic-dominant polarity of the exposition, for example--are never stated by Rosen but left to be gleaned by the reader. He also fails to spend enough time, in my opinion, discussing the ways in which minor-key sonata movements differ from the prevalent major-key models. Still, with careful reading, following some of the examples with recordings, and perhaps a bit of reordering, a comprehensive picture does emerge of one of the most important currents in Western tonal music. I still have to recommend this book as the best available on this knotty subject.