Several recent theories of linguistic representation treat the lexicon as a highly structured object, incorporating fairly detailed semantic information, and allowing multiple aspects of meaning to be represented in a single entry (e. g. Pustejovsky 1991; Copestake 1992; Copestake and Briscoe 1995). One consequence of these approaches is that word senses cannot be thought of as discrete units which are in one-to-one correspondence with lexical entries. This has many advantages in allowing an account of systematic polysemy, but leaves the problem of accounting for effects such as zeugma and the absence of crossed readings, which have traditionally been explained in terms of multiple lexial entries, but which can also arise in examples where other criteria demand that a single entry be involved. Copestake and Briscoe (1995) claimed that these cases could be explained by discourse coherence, but did not describe how this might work. We remedy this here by formalizing a general pragmatic principle which encapsulates discourse effects on word meaning. We demonstrate how it contributes to the creation of zeugma and the non-availability of crossed readings.