This paper discusses the semantics of the progressive aspect and defends
a substantially revised version of Terence Parsons's approach. The
revisions come in response to two main charges. The first is that
Parsons's account does not explain why `John crossed the street' entails
`John was crossing the street' (and in general, why perfective
accomplishments entail their progressive counterparts). The second is
that Parsons's account incorrectly predicts that `John is building a
house' entails `There is a house John is building' (and in general, that
the direct object of progressive accomplishments is available for
existential generalization).