The beautiful opening phrase conceals an unexpected fact: Beethoven starts the sonata off-key, on the dominant (E major). This start in medias res contributes to the openness and questioning character of many of the phrases, and later in the movement Beethoven develops this idea, systematically avoiding a resolution into the home key of A major. This turns out to be part of the sonata's design - Beethoven masterfully builds up a subconscious need for a resolution throughout the movements and manages to delay the appearance of a strong A major until much later in the sonata - the opening of the finale. This also fits with the development of the sonata form in Beethoven's late period, with the last movement increasingly becoming the main weight-bearer and focal aim of the entire work.
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