In this paper, we propose a unified account of the semantics of the English present progressive in the form of a semantic network, basing ourselves on the theoretical principles and analytical tools offered by the theory of Cognitive Grammar, as laid out by Langacker (1987, 1991). The core meaning of the English present progressive, we claim, is to indicateepistemic contingencyin the speaker's immediate reality. It thus contrasts with the simple present, which is associated with situations that are construed asstructurallybelonging to reality. On the basis of a study of the Santa Barbara Corpus of spoken American English, an inventory has been made of the more specific uses of the present progressive, temporal as well as modal. It is shown that each of these uses can be derived from this basic meaning of contingency in immediate reality via a set of conceptual branching principles, in interaction with elements in the context.