Oughtmust

Oughtmust is a coinage used in discussions of deontic and modal logic to denote a compound normative modality that blends the senses of ought and must. It is not a standard operator in formal logics, but appears in philosophical and linguistics literature as a way to model statements that are both reasonably supported by reasons and categorically obligatory.

The term is often introduced to illuminate differences between ought and must. Ought generally expresses a normative obligation grounded in reasons and can be defeasible or prima facie, whereas must conveys a stricter, necessity-like obligation. Oughtmust aims to capture situations in which an agent is required to act because there are sufficient reasons and, simultaneously, the duty is not easily overridden by convenient exceptions. One common formal reading treats oughtmust(p) as the conjunction of ought(p) and must(p), while another treats it as a graded or context-sensitive operator whose strength varies with circumstances such as feasibility or control.

Usage examples are primarily theoretical. A driver oughtmust stop at a red light when feasible and safe, representing a strong, reason-based obligation that resists easy avoidance. In theoretical work, oughtmust serves as a tool for comparing deontic logics that separate reasons-based obligations from necessity claims and for probing how conflicts between duties are resolved.

Critics argue that combining ought and must risks conflating distinct modal notions and can complicate analyses of feasibility, control, and exception handling. Yet as a conceptual device, oughtmust provides a framework for examining the intersection of practical reasons and categorical duties within normative theories.

See also deontic logic, ought, must, should, normative ethics, modal logic.