Ellipsis is subject to both syntactic conditions and discourse conditions. Here we explore the discourse condition that favors antecedents that are part of the main assertion of an utterance. We argue that the main assertion tendency is best captured in the processor, not the grammar. Two experiments test verb phrase ellipsis examples with antecedents in a conditional. One suggests that, because of the main assertion tendency, a reader considers full conditional antecedents and not just verb phrase antecedents. However, when the antecedent of the conditional expresses already given information and essentially becomes redundant, fewer full conditional antecedents are chosen for the verb phrase ellipsis, as if the consequent clause has become the assertion of the conditional sentence with the if-clause essentially cancelling out. The second experiment explores examples where a modal is added inside the if-clause, rendering the conditional counterfactual. As in other examples of flawed or imperfect ellipsis, the non-actuality entailment/implicature improves the acceptability of such examples.

VP-ellipsis and sluicing are forms of ellipsis that can cross a sentence boundary. We present a series of comprehension studies on these forms of ellipsis to elucidate their processing and the relation of syntactic and discourse processing. One set of studies examines the hypothesis that the representation of elided material is syntactically structured. We present evidence supporting the hypothesis and tentatively attribute the effects to sharing of the structure of the antecedent constituent, with structure building or substitution of a variable for a constituent permitted if it is licensed by the syntactic principles of the language. Another set of studies tests the hypothesis that a new utterance is preferentially related to the main assertion of the preceding utterance, which is typically a constituent high in the syntactic tree. The results suggest that discourse processing differs from syntactic processing, where the most accessible material is recent material found low in the syntactic tree. A final set of studies examines the interplay of the syntactic processor, which may not violate "islands," and the discourse processor, which may, in the processing of ellipsis sentences involving islands. A novel explanation is offered for the observation (Ross 1967) that sluicing out of relative-clause islands is grammatical except when sprouting is required.