Accommodation to an Unlikely Episodic State.

Mini-discourses like (ia) seem slightly odd compared to their counterparts containing a conjunction (ib). (i) a. Speaker A: John or Bill left. Speaker B: Sam did too. b. Speaker A: John and Bill left. Speaker B: Sam did too. One possibility is that or in Speaker A's utterance in (ia) raises the potential Question Under Discussion (QUD) whether it was John or Bill who left and Speaker B's reply fails to address this QUD. A different possibility is that the epistemic state of the speaker of (ia) is somewhat unlikely or uneven: the speaker knows that someone left, and that it was John or Bill, but doesn't know which one. The results of four acceptability judgment studies confirmed that (ia) is less good or coherent than (ib) (Experiment 1), but not due to failure to address the QUD implicitly introduced by the disjunction because the penalty for disjunction persisted even in the presence of a different overt QUD (Experiment 2) and even when there was no reply to Speaker A (Experiment 3). The hypothesis that accommodating an unusual epistemic state might underlie the lower acceptability of disjunction was supported by the fact that the disjunction penalty is larger in past tense discourses than in future discourses, where partial knowledge of events is the norm (Experiment 4). The results of an eye tracking study revealed a penalty for disjunction relative to conjunction that was significantly smaller when a lead in (I wonder if it was…) explicitly introduced the disjunction. This interaction (connective X lead in) appeared in early measures on the disjunctive phrase itself, suggesting that the input is related to an inferred epistemic state of the speaker in a rapid and ongoing fashion.