Beethoven gave this sonata the unusual title 'Sonata quasi una Fantasia', which it shares, along with its opus number, with the considerably more famous 'Moonlight' Sonata. Both sonatas – along with the preceding sonata with the funeral march op. 26, and the three sonatas op. 31 soon to follow – usher in Beethoven's conquest of new musical territory in this genre.

With a complex structure that oscillates between fantasia and sonata, op. 27 no. 1 has long presented pianists with great interpre...