Composed in 1804. Two movements.
It's hard not to feel a bit of pity for the Op.54 – it’s a little thing jammed right between the massive Waldstein and Appassionata, and even though it’s every bit as radical as those behemoths it’s practically unknown and rarely performed. This is probably because its radical nature is expressed in a way that makes it hard to pin down; the Waldstein is bright, and Appassionata is dark, and the Op.54 is – well, what, exactly? Happy? Delicate? Tipsy? I suppose the way to put it is this: it’s structurally very odd, but in a rather gently misleading sort of way.
Take the first movement, which is in ABABA form. The A section is formed from a theme that’s designed to have no hint of tension or progression in it; all of its 8 phrases end in the tonic. The B section has a theme that (a) basically isn’t a theme, being formed of just brusque octaves, (b) modulates without preparation, (c) suddenly decides to shift midway to 2/4 time, and (d) has suddenly become a *lot* shorter the second time it appears. The only real development you get is the decoration of the A theme each time it appears, and the whole movement is built almost entirely around the contrast between the two themes. this is also a feature of some of the very latest sonatas, in particular the Opus 109 in E Major.
The second movement is even weirder. It's in sonata form, but either the exposition doesn't give you the full theme (and yes, it's basically monothematic, with what could be a new idea in development), or the recap itself continues to aggressively develop the theme. And the whole texture of the movement is surprisingly Chopinesque: it is a very pianistic perpetuum mobile in harmony of two parts on a single theme, with a strange accent. The only texture this movement seems to know is counterpoint, the only counterpoint it seems to know is 2-part counterpoint, and the only type of 2-part counterpoint it knows about is basically, well, arpeggios. Tonally, it moves between melodious farce and direct drama and is modulated with abandon in distant tones, in contrast to the more typical dominant tonic scheme of the first movement.