Ferdinand de Saussure

Swiss linguist whose ideas on structure in language laid the foundation for the structuralist school in linguistics and social theory. The whole line from Jakobson to Lévi-Strauss to Althusser to Foucault and Derrida trace their ideas back to Saussure’s simple idea that the meaning of a word is to be understood through its relation to other words, as opposed to the positivist line of research dominant in his day, which sought to understand language through analysis of sounds and their imapct on the nervous system.
While still a student, Saussure established his reputation with a brilliant contribution to comparative linguistics, Memoir on the Original System of Vowels in the Indo-European Languages. In it, he explained how vowel alternations in Indo-European languages take place. Though he wrote no other book, he was enormously influential as a teacher, lecturing at the ةcole des Hautes ةtudes in Paris from 1881 to 1891 and as professor of Indo-European linguistics and Sanskrit (1901-13) and of general linguistics (1907-13) at the University of Geneva. His name is best known, however, for theCourse in General Linguistics, a reconstruction of his lecture notes and other materials by two of his students.
Saussure contended that language must be considered a social phenomenon, a structured system that can be viewed synchronically and diachronically (in the course of time) but he insisted that the methodology of each approach is distinct and mutually exclusive. He also introduced two terms that have become common currency in linguistics - “parole,” the speech of the individual person, and “langue,” the systematic, structured language (such as English) existing at a given time within a given society. These are ideas are usually regarded as starting point of Structuralism in Linguistics.

For more information:
http://en.wikipedia.org/wiki/Ferdinand_de_Saussure
http://www.anotherscene.com/sempsych/spsaussure.html
http://www.press.jhu.edu/books/hopkins_guide_to_literary_theory/ferdinand_de_saussure.html