A work from 1802, widely beloved among Beethoven's piano sonatas for its popular melody. Beethoven himself titled it 'Sonata quasi una Fantasia' (Sonata in the manner of a Fantasy), while the popular name 'Moonlight' derives from a comment by the poet Ludwig Rellstab ('like a boat rocking in the moonlight on Lake Lucerne'). Rellstab is known, among other things, for having written the lyrics for Schubert's Lieder.

The solemnity and spirituality of the first movement, combined with its romanticism, might evoke the image of a nocturne; however, it is also imbued with a tone that can only be described as resignation, which transcends such a simple explanation. When this is unleashed with intense fervor in the third movement, it suggests that this emotional outburst may stem from something deeply personal. One can almost envision Beethoven standing firm amidst the irresistible forces of a storm, of lightning.

The circumstances under which composers create their works are diverse. They include dedications, longing, nostalgia, anti-establishment sentiments, and, of course, human relationships. Beethoven was no exception; his feelings for Giulietta Guicciardi, to whom he dedicated this work, characterize the piece. Her presence, which he sometimes confided to acquaintances in letters as that of a 'lovely, enchanting girl,' marked a very bright turning point in his life. However, in the aforementioned letters, he also confessed that this love would likely not be fulfilled due to differences in social standing. Furthermore, among his numerous collected letters, no letters addressed by Beethoven to Guicciardi have been found. This sonata, as if Beethoven were confiding his innermost feelings through sound, evokes less the gentle impression of moonlight and more the image of Beethoven the composer resolutely confronting life, a rare glimpse of his back.

At that time, Beethoven was undergoing a transitional period, in a sense, as he assimilated and studied traditional genres such as piano sonatas and string quartets while striving to tackle new compositional challenges. Regarding this work, as its title 'Fantasia' suggests, one can observe various innovative ideas, such as the incorporation of improvisatory elements and the first conscious and detailed notation of pedal (then operated by a knee lever) usage in the first movement. The numerous works from this period would blossom into the 'forest of masterpieces' that he would enter after composing his Heiligenstadt Testament in the same year.