He is noted for interdisciplinary work on the interface of linguistics and philosophy—in particular on the philosophical foundations of Noam Chomsky's theory of generative linguistics and on the foundations of the theory of meaning in linguistic semantics.
Han er især kendt for sit tværfaglige arbejde om forholdet mellem lingvistik og filosofi, især det filosofiske fundament for Noam Chomskys generative lingvistik og grundlaget for teorien om mening i sproglig semantik.