In this paper we propose to focus on so-called speech genres,traditionally understood as a set of tacit instructions broadly constraining the form and content of our discursive productions.More specifically,and according to Peirce’s categorial scheme,we suggest speech genres can be considered as‘thirds’,or purposeful and general‘laws’overdetermining speech and its regularities.As such,the study of their semiotic mechanisms would fall within the sphere of Peirce’s‘speculative rhetoric’,one of the three branches of his semeiotics.Overall,following Lyne,we suggest that any speech genre relates to three kinds of rhetorical‘habits’—habits of representation,habits of objectification,and habits of interpretation—which explain a sense of‘reasonableness’permeating any discursive practice in society.We suggest that the task of discursive rhetorics should be to delineate,for given cultural communities,the productive and interpretive norms and mechanisms which govern the determination of discourse and elicit an intended interpretation on the interpreter’s side.