 A more influential attempt to expand on this component of intention-based semantics has been given by Stephen Schiffer.Grice's most influential contribution to philosophy and linguistics is his theory of implicature, which started in his 1961 article, 'The Causal Theory of Perception', and was most fully developed in his 1967 "Logic and Conversation", at Harvard's 'William James Lectures'.According to Grice, what a speaker means by an utterance can be divided into what the speaker "says" and what the speaker thereby "implicates".