My early research was in information theory and communication theory. Since 1958, I have been working almost continuously on problems that overlap computer science and linguistics. Much of this research is now classified under formal linguistics, natural language processing, artificial intelligence, or cognitive science, depending on the topic. These categories are not necessarily exclusive.
More specifically, I have been working on syntactic and semantic representations for language structure, relationship of language structure to logic, mathematical linguistics, theory of computation as it relates to natural language processing, parsing algorithms, design and implementation of various systems for natural language processing, especially question-answer systems as interfaces to databases, theories of representation and inferencing in natural language, computational aspects of discourse, psychological implications of processing models, problems in processing certain kinds of bilingual utterances, some aspects of language learning, and other related problems.