My kingdom for a horse

Promising and warning are speech acts that have to be credible to be persuasive. The question is: When does a promise become incredible and a warning unpersuasive? Whereas credibility has been researched from a social persuasion perspective, this article answers that question empirically, from an adaptive heuristics perspective. First, we present a satisficing algorithm that discriminates conditional promises, threats, advices, and warnings by pragmatic cues. Then, we discuss an alternative model of this algorithm that further accounts for the credibility of these conditionals by formal principles, and also adds two hypotheses: (1) Threats but not promises are more credible with proportionate than disproportionate consequences, and (2) Both advices and warnings are more persuasive with bilateral than unilateral consequences. Finally, we present two experiments and their follow-ups that, consistent with the pragmatic algorithm, provide evidence against both hypotheses.