This thesis examines the dispute over the word casament (marriage) in the contemporary debate on the civil rights of homosexual couples in Brazil. It assumes a discursive-pragmatic perspective that focuses on some of the main propositions of Michel Foucault, who, in his work The Discourse on Language, recognized that words translate not only systems of domination, but also, and above all, that by which and for which we fight: instruments of power. This thesis analyzes speeches for and against the institutional use of the word casamento when referring to homosexual couples, in a representative set of recently published texts in print and digital media. A mapping of the main types of arguments used by either side is carried out. The research shows in particular (a) the prevalence of the exclusive religious argument, especially in arguments against the use of the term, (b) the incidence of similar arguments to support opposing viewpoints, (c) the partial convergence between the Brazilian case and the Argentine, Spanish and Portuguese cases (covered in a recent study by Bruno Bimbi) and (d) the ways in which the discussion examined instantiates the internal and external procedures of rarefaction within discourse that Foucault elaborates in the work cited above.