With expertise ranging from linguistic theory to poetics to Sanskrit grammar, Paul Kiparsky has long been a leader regarding theoretical aspects of language structure and their historical development. His influential 1965 dissertation and major articles in 1960s/1970s set the agenda for studying sound change, and language change more generally, within the Chomskyan Generative Grammar framework. His ongoing theoretical and diachronic contributions go beyond sounds, encompassing word and sentence structure. His Lexical Phonology theory provided a viable alternative to then-prevailing theories of Noam Chomsky and Morris Halle. Relatedly, his 1979 book explicated previously ill-understood aspects of the 2500-year-old Indian grammatical description.