Linguistics has had a major impact on twentieth-century literary theory, primarily through the influence of the Swiss linguist, Ferdinand de Saussure (1857–1913). Saussure argued that linguistics should move from a diachronic study of language, that is, how language develops historically, to a synchronic study, that is, treating language as a system within one temporal plane. He divided language into "langue", the underlying system that governs linguistic usage, and "parole", how language is actually used in practice. The basis of "langue" is that words are arbitrary signs in that the relation between a word and what it signifies is arbitrary, that is, almost entirely determined by convention. What determines meaning is not that a word refers to the world or to ideas or concepts that exist outside of language; it is the differences between linguistic signs themselves that create meaning. Saussure's shift of linguistic emphasis to language as a signifying system paralleled developments in formalistic criticism and his work has been most influential on those who favour a formalist approach.