The early piano trio, the two piano concertos, the three piano sonatas and the late cello sonata op. 65 comprise Chopin's few contributions to sonata form, the principal form of the Classical era. Especially the two Piano Sonatas opp. 35 and 58 fully deserve their reputation as two of Chopin's most distinctive creations.
The b flat minor Sonata was written in 1839, but the funeral march that made it famous had seen the light of day two years earlier. Its combination of free and structured form, of passion and clarity, gave birth to a work of incomparable mastery crowned with a highly original final movement: 75 measures of surging, unison eighth-note triplets.