It's not just sounds that can cause dismay: how about quarter notes? This morning the uncomfortable quarter note appeared in the early E-flat Sonata of Mozart: An innocent tonic chord in root position perched almost intolerably on the second beat of the bar, dying to move.

We don't usually think of rhythm as dissonant, especially in music of the Classical period. But there it is, impudent as all get-out, the teenage Wolfgang writing something his father surely did not approve of--as my student put it: "Like rock and roll."