Sorry for the pun: It just slipped out.
Thinking about upbeats and downbeats, as I do a great deal of the time, brings to mind the many instances in which a composer combines rhythmically ambiguous material with fermatas (as does Schubert in the B-flat Sonata, so much on my mind of late). Having the same sonority on both sides of a bar line is one way to obscure the down-beat. Ending a phrase with rests and a fermata further obscures matters, especially if you take the fermata to mean that a period of time must elapse such that the listener has no idea whether the next sound is a down- or an up-beat (cf. my definition of fermata in What Might it Mean? An Uncommon Glossary of Musical Terms and Concepts for the Stuck, Bored, and Curious).
There are two schools of thought on the subject one maintaining that the downbeat as notated must be audible at all costs and in all cases, the other, finding this predictability to be conducive to physical and mental torpor, avoiding it like the plague.
