In almost all of his writings on ontology, Quine celebrated the discovery of contextual definition as a milestone of the history of philosophy. The philosophical appeal of this tool resides in the hope that it allows us to reduce the ontological commitments of theories in substantial ways. The goal of this paper is to show that contextual definition does not really come up to this hope. It is argued that the material adequacy of such definitions presupposes a very strong context-principle, (...) one implying that theories do not have any ontological commitments at all. (shrink)