He has traditionally been referred to as the “bridge to romanticism,” and his output is simplistically divided into three roughly equal periods. Today most scholars view him as the last great representative of the Viennese classical style, a composer who at two important junctures in his life turned away from the aesthetic of the emerging romantic period in favor of renewed exploration of the legacy of Haydn and Mozart. After arriving in Vienna Beethoven alternated between compositions based openly on classical models, such as the String Quartet in A Major op. 18 no. 5 (1800; patterned on Mozart's String Quartet K. 464) and those based on looser Italianate structures, such as the song “Adelaide” (1795).
The “new manner” that Beethoven referred to in 1802 marks his first return to the Viennese classical tradition. Although his works of the decade 1802-12 project a heroic aura, musically they represent an expansion of the tighter forms of Haydn and Mozart. This is apparent both in works of unprecedented scope, such as the Eroica Symphony and the Piano Concerto no. 5 (Emperor, 1809), and in stylistically compressed works such as the Symphony no. 5 (1808) and the Piano Sonata op. 57 (Appassionata, 1805). In these works he proved that a style founded on unprecedented thematic integration and on the harmonic polarization achieved by manipulating opposing keys could produce works of remarkable expressive power.
The completion of the Symphony no. 8 and the fading of hopes for a successful relationship with the “Immortal Beloved” left Beethoven in a sea of compositional uncertainty. The prodigious output of the previous decade ceased. The few works of the years after 1812—such as the op. 98 song cycle An die ferne Geliebte (To the Distant Beloved, 1816) and the Piano Sonata in A Major op. 101 (1817)—took on an experimental hue, reviving and expanding on the more relaxed musical structures Beethoven had employed in the 1790s. This handful of open-ended, cyclic works of this period exercised the most direct musical influence on the succeeding generation of romantic composers (apparent, for example, in the song cycles of the German composer Robert Schumann).
In 1818 Beethoven inaugurated a second return to the tightly structured “heroic” style. The move was marked by the Piano Sonata in B-flat Major op.