From Syntax to Natural Logic – Lauri Karttunen (PARC)
Computational Linguistics is again becoming an exciting field for linguists because it is moving from information retrieval to understanding and reasoning. This requires the integration of syntax and semantics. Natural Logic is a cover term for a family of formal approaches to semantics and textual inferencing as currently practiced by computational linguists. They have in common a proof theoretical rather than a model-theoretic focus and an overriding concern with feasibility.In this context, the old insights on lexical classes such as implicatives and factives are being resurrected, implemented and extended. Like the term “natural logic” itself, the original work dates back to the 1970s. I will discuss specific problems of textual inference that involve veridicity, issue of whether the proposition expressed by a complement clause is entailed by the sentence that contains it. I will demonstrate how this issue is handled in the Bridge system built at the Palo Alto Research Center, one of the early promoters of the RTE (Recognizing Textual Entailment) challenge.
Lauri Karttunen is known for his seminal contributions to the semantics of discourse referents, implicatives, presuppositions, and questions in the seventies and eighties. In the area of computational linguistics, Karttunen was one of the first pioneers to realize and exploit the potential of finite-state transducers for linguistic applications such as morphological analysis. His early work on the logic of complementation has turned out to be fundamental for computing local textual inferences of complex sentences, the topic of his current interest. In 2007 Karttunen received the Lifetime Achievement Award from the ACL (Association for Computational Linguistics).