This paper aims at analyzing the semantics and pragmatics of Persian modal verbs based on Papafragou's (1998, 2000) relevance-theoretic model. Persian modals are defined in terms of logical relations and propositional domains. According to the findings of the research, two of the three modals, namely, 'sodan' and 'tavan' express the logical relation of compatibility with respect to different propositional domains: the three forms 'misavad, misod' and 'misode' are unspecified with respect to their propositional domains and take them directly from the context, whereas 'betavan' and 'besavad' accept the desirability domain. 'Mitavan' also expresses compatibility in relation to the propositions in the factual domain. However, 'b'yad' is the only modal that encodes the logical relation of entailment and is unspecified with respect to the type of propositional domain it accepts.