Both Op. 27 sonatas outline a gradual progression from ‘static’ circular structures to dynamic linear processes; from ‘content-based’ ambiguous forms to finales that can be understood against normative models like sonata form and rondo. While all but one of their movements are structurally self-sufficient and can be perceived as discrete segments, Beethoven asks for them to be run together in performance to give the impression of a continuous whole. Structurally this integration is supported by the large tonal patterns governing each work: C♯ is the tonic for all three movements in the second sonata; and the first sonata's movements, though encompassing a wider tonal range, are enmeshed together by an interlocking series of tonics (bracketed in Figure 5.1).

An impression of continuity is reinforced at a more detailed level by the cohesive actions of motivic integration and gestural recall: ideas from the opening movements return transformed in the dynamic context of the finales. Yet from moment to moment the musical continuity is often threatened by Beethoven's allusions to musical spontaneity. The threat comes to the fore most obviously in cadenza-like passages and in disjunctions of tonality, tempo, idea, register, and texture. In this respect some critics have detected a stronger element of the fantastic in the E♭ sonata than in the ‘Moonlight’: while the element of Willkür is perhaps less prominent in the second sonata, Czerny regarded the first as a paragon among strictly composed fantasies.