IISER MOHALI

Abstract: This lecture offers a critical exploration of possible world semantics and its application to deontic modal logic, the formal study of normative expressions involving the categories of obligation, permission, and prohibition. Beginning with a conceptual overview of possible worlds—those hypothetical scenarios used to interpret modal claims—the session will trace how this semantic framework has been extended to deontic contexts. While standard approaches attempt to model normative reasoning by treating obligations as truths across ideal worlds or alternative moral worlds, this lecture problematizes such applications. It argues that the use of possible world semantics in deontic logic often yields results that are either trivial or counterintuitive, failing to capture the nuanced structure of normative expressions. To address this, the lecture offers the D-Model, a quasi-formal device, to capture the formal structures underlying deontic expressions—a project akin to Russell’s analysis of definite descriptions. Though the D-Model employs the notion of possible worlds to analyze the logical form of deontic expressions, it does not offer a semantic model in the traditional sense. It is hoped that the discussion will result in a deeper appreciation of both the power and the limitations of modal semantics in normative domains—and a fresh perspective on how formal inquiries at the foundational levels can illuminate the structure of ethical and legal reasoning.