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. In contemporary formal semantics, situation-based approaches include both the original Barwise–Perry programme and a more widely adopted family of theories (associated especially with Angelika Kratzer) that treat situations as parts of possible worlds and use situation variables in otherwise orthodox possible-worlds semantics.
History
Origins in Barwise and Perry Situations entered formal semantics through Barwise's paper "Scenes and Other Situations" (1981), which analysed naked infinitive perception reports such as Beryl saw Meryl feed the animals in terms of an actually perceived situation that supports the embedded clause, rather than in terms of propositions alone. Related papers by Barwise and Perry developed a broadly similar approach to belief reports and other problematic constructions. The book Situations and Attitudes (1983) provided the first systematic statement of situation semantics. It proposed that linguistic meaning should be understood in terms of relations between three kinds of situations: a discourse situation (in which an utterance is produced), a resource or connective situation (representing background information, constraints and shared context), and a described situation (the situation talked about). The framework was designed to capture how speakers use information available in limited parts of the world to talk about other parts, and to account for so-called "semantic universals" such as the external, information-conveying role of language.
From situation semantics to situation theory Early formulations of situation semantics faced foundational problems when cast in standard well-founded set theory, especially when modelling information flow and self-referential structures. Building on Peter Aczel's work in non-well-founded set theory, Barwise and colleagues developed situation theory as a general theory of information with a rich ontology of situations, infons, types and constraints, and used it to reformulate the semantic programme. Keith Devlin's work in the late 1980s and early 1990s further systematised situation theory, introducing infons as formal items of information and emphasising the distinction between information, its content and its various representations. Situation theory subsequently developed into a general interdisciplinary framework for modelling information in logic, linguistics, philosophy of information and computer science.
Criticism and later developments Barwise and Perry's original proposals for perception reports were challenged by, among others, James Higginbotham, who argued for an extensional alternative based on Davidsonian event semantics. More generally, critics observed that many of the empirical motivations for situations could be addressed in frameworks that kept standard possible-worlds machinery while enriching it with events or additional parameters. Although the specific Barwise–Perry framework lost much of its momentum in the early 1990s, a situation-based perspective remained influential. Kratzer and others developed a strand of situation semantics that treats situations as parts of possible worlds and uses them to model topic situations, domain restrictions and fine-grained content. According to Barbara Partee, such "possible-worlds-based" situation semantics has had more impact on mainstream formal semantics than the original information-theoretic programme of Barwise and Perry.
Basic ideas
Situations In situation semantics, situations are limited, concrete parts or aspects of the world that an agent can in principle perceive, keep track of and reason about. They are often described as "small worlds" containing individuals standing in relations and having properties at particular times and locations. Situations can include, for example, a particular episode of feeding animals, a traffic intersection at a given time, or a specific conversational exchange. Unlike complete possible worlds, situations are incomplete: for many propositions p, neither p nor ¬p need be settled by a given situation. This partiality is central to the programme: language users typically have access only to limited parts of reality, yet they use information available in those parts to draw conclusions about other parts.
Infons and information content Later formulations of situation theory and situation semantics introduce infons as abstract items of information. Intuitively, an infon corresponds to a simple state of affairs, such as an object having a property or a tuple of objects standing in a relation. A common notation represents infons as tuples of the form ⟨R, a1, ..., an, p⟩, where R is an n-place relation, the ai are objects, and p is a polarity indicating whether the information is positive or negative. Given a suitable ontology of situations and infons, situation theory distinguishes several key relations:
A situation s supports an infon σ when σ is part of the information that actually obtains in s (roughly, when the corresponding state of affairs holds in s). A situation carries an infon σ when, by general constraints, support for some infons in s guarantees σ, possibly about another situation. On this view, information flow is governed by constraints—some nomic (laws of nature), some conventional (linguistic or social conventions), some logical or mathematical. These constraints explain how limited local information can yield knowledge about more remote or abstract aspects of the world.
Meaning as relations between situations In the original Barwise–Perry framework, the meaning of an utterance is analysed as a relation between:
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