In this paper, we show how the problem of accounting for the semantics of t
emporal preposition phrases (tPPs) leads us to some surprising insights int
o the semantics of temporal expressions in general. Specifically, we argue
that a systematic treatment of English tPPs is greatly facilitated if we en
dow our meaning assignments with context variables, a device which allows a
tPP to restrict domains of quantification arising elsewhere in a sentence.
We observe that the use of context variables implies that tPPs can modify
expressions in two ways, and we use this observation to predict the behavio
ur of tPPs whose complements are themselves modified by other tPPs.