Semantics

Semantics research is about how the meaning of a sentence is determined from its parts and the way the parts are put together. Semantics at Penn focuses on several new approaches to the field, including LTAG semantics and underspecification as well as the application of game theory.

Maribel Romero and Robin Clark lead Penn's research in formal semantics, mathematical linguistics, and computational semantics. Romero's work on the interfaces between semantics, syntax and pragmatics has covered a broad variety of topics, including ellipsis, focus, questions, conditionals, disjunction, reconstruction, presupposition, indefinites, negation, and epistemic bias. She has more recently been pioneering underspecified semantics in the framework of Multi-Component Lexicalized Tree Adjoining Grammar along with TAG's creator, Aravind Joshi. Weekly XTAG meetings serve to bring together the various lines of TAG research happening at Penn.

Clark has been pursuing a line of research that began as an attempt to address the issue of language learnability. About a decade ago his work on Kolmo­gorov complexity led him to an automata-theoretic characterization of quantifiers. He then needed to confront the fact that, while first-order quantifiers can be simulated with finite-state machines, more complex quantifiers require more complex machines and more memory. Since it seems likely that processing different types of quantifiers might involve different parts of the brain, Clark is collaborating with Murray Grossman of the School of Medicine to test that hypothesis experimentally.

His unique perspective on linguistics has led him to pursue a new game-theoretic approach to the semantics of quantifiers and more generally a model of meaning rooted in the cooperative interaction between social agents. He is now collaborating with Prashant Parikh on the analysis of discourse anaphora using classic game theory; they have extended the game-theoretic analysis to other semantic and pragmatic problems. Clark introduces his students to important alternative approaches to semantics, including game theory and Categorial Grammar, which has been advanced by former Penn professor Mark Steedman.