Occasionalism and the Problem of Impenetrability

In the European tradition, occasionalism is strongly associated with Cartesianism. One potent challenge to Cartesian occasionalism, raised in the 17th century by Bernard de Fontenelle, goes like this: Cartesian corporeal ontology is inconsistent with occasionalism in the corporeal domain because impenetrability is conceptually derived from the material essence and a causal power. This paper, therefore, poses the question: Did Fontenelle show that Cartesians cannot be occasionalist? It also answers this question in the negative by arguing that Descartes's writings on impenetrability show that he does not understand impenetrability to be a causal power.