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 thefuneral march op. 26, and the thre 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 longpresented pianists with great interpretive chall