English summary: Louis Hjemslev (1899-1965), the second most important figure, after Saussure, in structural linguistics, founded the Copenhagen Circle, a group that played an eminent role on the international scene in the early 1930s, particularly because of the controversy that opposed itto the Prague Circle, led by Jakobson and Troubetzkoy. But the "glossematics" that Hjemselv created did not gain widespread acceptance, and if his work is still being studied, it is because of those of his theoretical proposals whose scope extended beyond the strict framework of linguistics. In fact, in his work, Prolegomenes a unetheorie du langage, Hjemslev presents a theory of knowledge that still interests today's semioticians andphilosophers, as well as everyone in the field of human sciences who wishes to pursue epistemological queries. This theory supports a relativistic conception of knowledge based on two original concepts: "metasemiotics" and "connotative semiotics" - concepts amply covered in this book.Semir Badir is a Researcher at the Fonds National Belge de la Recherche Scientifique and teaches at Universite de Liege. He is the author of Metalinguistique saussurienne. French description: Figure majeure, apres Saussure, de la linguistique structurale, Louis Hjemslev (1899-1965) fut a l'origine du Cercle de Copenhague qui, au debut des annees trente, tint un role eminent sur la scene internationale, en particulier par les controverses qui l'opposerent au Cercle de Prague, mene par Jakobson et Troubetzkoy.Pourtant, la glossematique creee par Hjemslev ne fit guere ecole, et si son oeuvre continue d'etre etudiee, c'est surtout en vertu des propositions theoriques qui debordent du strict cadre de la linguistique. De fait, dans ses Prolegomenes a une theorie du langage, Hjemslev presente une theorie de la connaissance qui continue d'interesser semioticiens et philosophes, ainsi que tous ceux qui, dans les sciences humaines, veulent poursuivre des interrogations epistemologiques. Cette theorie defend une conception relativiste du savoir en s'appuyant sur deux concepts originaux: la metasemiotique et la semiotique connotative, concepts dont ce livre propose une ample presentation.