Still the most startling of the late quartets, Beethoven's String Quartet in A minor, Op.132 is the one that fascinates me the most. It is the most extreme and diverse of the quartets, ranging for passionate intensity to near emotional neutrality, from radiant simplicity to deep complexity, from gratitude to what some see as mockery.
Music analysts have always had a bit of a field-day trying to pin down the structure of the opening movement. It doesn't seem to do what conventional sonata form first movements ought to do. For what it's worth I'd describe it as an exposition followed by a developing recapitulation followed by a further varied recapitulation and coda. Hope that helps! The development of the themes is unusual too. The main theme is a symbiosis of two contrasting ideas, The first is a haunting theme in long notes based entirely on permutations of a four-note motif. The allegro counter-subject is more melodic, though various internal repetitions of pitch and rhythm render it ripe for development. From the latter's opening notes Beethoven then grows a very attractive lyrical melody which seems to function less as a second subject than as relief (brief as it is) from the profound sense of emotional involvement conveyed by the conjoined main theme. Please listen out for the awe-inspiring quiet return of the long-note idea in canon at the start of the first 'developing recapitulation' and the swinging, syncopated variant of it that follows - details in a very beautiful and thoughtful musical argument. This is one of Beethoven's best movements.
Another conjoined theme virtually monopolises the Scherzo's emotionally uninvolved main section - two six-note ideas, one rising, one falling, each in a distinct rhythm. They dance coolly, without kissing - so to speak! The trio is a very different kind of dance - a magical musette, evoking bagpipes with a drone and an enchanting tune in lengths. Its own central section is a more earthbound ländler (country dance).
If there's one movement among Beethoven's late quartets that remains difficult, even in our own heard-it-all age it's the Adagio of this quartet - the Heiliger Dankgesang eines Genesenen an die Gottheit, in der lydischen Tonart ('Holy Song of Thanksgiving to the Deity by a Convalescent, in the Lydian mode.') The structure is A,B,A',B',A''. The dramatic contrasts between the slow, otherworldly 'A' sections and the fast, flesh-and-blood 'B' sections is like a microcosm of the quartet as a whole, albeit heightened to unprecedented levels. The 'B' sections convey the feeling of renewed strength after illness (the composer had just survived a particularly serious bout of influenza), the second 'B' section being 'stronger' than the first. These bursts of vitality seem almost ordinary next to the unquestionably extraordinary 'A' sections. These remarkable hymns of gratitude to God stick fixedly to Lydian F, singing their beautiful chorale at heavenly length in long, stretched-out notes. No other music I know conveys timelessness and/or eternity so strongly. The two later 'A' sections are variations of the first and the final one transcends the others, attaining true sublimity. The serene final 'A' section is one of the most beautiful things ever written.
After this encounter with the sublime comes a surprise, a shock even - a short, naive-sounding march in a spirit of such cheerfulness that we (with our ears attuned to Mahler and Shostakovich) might suspect the composer of being ironic. With it comes and idea that can, in some performances, be made to sound sarcastic - a operatic recitative. I don't think it's Beethovenian mockery at all. I would say the movement as a whole is simply a burst of genuine good humour (as the wonderful performance I've linked to makes clear). However you read it this recitative leads straight into...
...the Allegro appassionata finale - a movement worthy to conclude this great quartet. It takes the form of a rondo, having a superb main theme - a great lilting yet tragic melody. The appassionata marking conveys the spirit of the movement's episodes, one of which nears violence and might make you think of the Expressionism of a century later (though that also depends on the interpretation placed on it by the performers). The final Presto is gloriously unexpected - were it not for the fact that the unexpected keeps happening in this piece.
Mahler famously told Sibelius, "The symphony must be like the world. It must embrace everything." Beethoven's A minor String Quartet was there nearly a century earlier, embracing everything, being like the world.