Genre theory, as it has developed in the last forty years, has made use of what I call a constitutive concept of genre, a concept that has built into it the assumption that genre plays a central epistemic role in the interpretation of verbal discourse. In this paper I argue that there are theoretical problems with such a concept that have not been recognized and that make it unsuitable as a critical instrument in literary history and literary studies. A fruitful concept of literary genre needs to be pragmatic with only a heuristic and not an epistemic function. As an example, the article looks at the criticism produced in connection with the picaresque novel and in particular at the account given of the origin of the genre, an account that could not have been given if one had employed a constitutive concept of genre.