Géraud de Cordemoy's (1626–84) contribution to linguistics is found in the Discours physique de la parole. This work aims at analyzing the respective roles of body and soul in the use of language, in an attempt to bring new proofs of Cartesian dualism. Cordemoy first distinguishes between natural signs and conventional (‘d’institution') signs. He then researches the mechanical laws at play in the production of sounds in language and gives detailed descriptions in articulatory and acoustical phonetics. These examinations are based on the study of language acquisition in children and nonnative speakers.