John Perry (philosopher) in the context of University of California, Riverside

Situation semantics is a framework in formal semantics and situation theory in which the meanings of linguistic expressions are evaluated with respect to situations—partial, concrete parts or aspects of the world—rather than complete possible worlds. It was developed in the late 1970s and early 1980s by Jon Barwise and John Perry as an alternative to extensional model theory and possible-worlds semantics, with a particular focus on perception reports, attitude reports and other context-dependent constructions in natural language.

Situation semantics is underpinned by situation theory, a general mathematical theory of information developed by Barwise, Perry, Keith Devlin and others, which introduces formal objects such as infons (units of information), constraints and types to model how information is carried and flows between situations.

Situation theory is a mathematical and logical framework for modelling information, partial states of affairs and their structure. It was introduced in the early 1980s as the formal background for situation semantics developed by Jon Barwise and John Perry, and has since been elaborated by authors such as Keith Devlin, Jeremy Seligman and Lawrence S. Moss into a general theory of information and information flow. In many presentations the mathematical foundations make essential use of non-well-founded set theory, especially Peter Aczel's anti-foundation axiom, in order to model self-referential and other "circular" informational structures.

The relation between situation theory and situation semantics is often compared to that between type theory and Montague semantics: situation theory provides a general mathematical ontology (infons, situations, types, constraints), while situation semantics applies that ontology to natural-language meaning and context dependence.