When you want to argue whether Beethoven acted on impulse or not, think
about how he used to improvise the cadenzas in his concerti.  It wasn't
later until composers started to actually write down the cadenza.  Before
that the pianist, who was usually the composer himself, would use the
cadenza almost like a showcase after the orchestra finish playing, almost
like the drummer will do take a solo towards the end of a song in a jazz
band concert.  Impulse...Impulse...SPONTANEITY!!!!!!

Jeremey