He published Syntactic Structures a theory of...

The correct answer is generative grammar. This is because "Syntactic Structures" is a book written by Noam Chomsky, in which he introduces the concept of generative grammar. Generative grammar is a linguistic theory that aims to explain how sentences are generated in the human mind and how they can be transformed into different structures. Chomsky's theory of generative grammar revolutionized the field of linguistics and had a significant impact on our understanding of language acquisition and processing.