Contextual expectations and norms of evidential disclosure in assertion

What evidential basis is expected when a speaker makes an assertion, and under which circumstances does an audience require its disclosure? Truth commitment accounts of assertion grounding hold that the speaker is accountable for the veracity of the propositional content, but they do not specify the type of evidence – in particular, direct or indirect – which has to ground it. In this experimental study we investigated the sensitivity of listener expectations regarding speaker evidence and the conversational norms that regulate when speaker evidence should be disclosed. We found that (i) contextually shaped expectations about sources of evidence, which can be direct as well as indirect, ground assertions, and that (ii) these expectations set a reliability threshold such that speakers are expected to use a reportative evidential when their actual evidence is less direct than expected, but not when it is more direct.