Competence by default: do listeners assume that speakers are knowledgeable when computing conversational inferences?

Abstract When engaged in conversation, do listeners make default assumptions about the epistemic states of speakers? According to some accounts, when listeners hear a sentence like “Sarah solved some of the math problems,” they infer by default that speakers believe that the stronger statement involving “all” is false (i.e. that Sarah did not solve all of the problems). However, drawing on tests of reading time, eye tracking, and manipulations of cognitive load, multiple studies have argued that this form of inference (i.e. strong scalar implicature) is not computed by default. In this study, while acknowledging this claim, we explore whether important subprocesses of implicature might nevertheless involve default inferences. In particular, we tested whether listeners assume by default that speakers are knowledgeable about alternative utterances that are left unsaid—a critical precondition for computing strong scalar implicatures. To do this, we tested 60 English-speaking participants who heard utterances made by either knowledgeable speakers or ignorant speakers. In addition, half of these participants were placed under cognitive load using a dot-array memory task. We found that participants placed under load over-computed implicatures when speakers were ignorant, as though assuming that they were knowledgeable by default.