The Structuralist Criterion of Ontological Commitment in Quine’s Mature Philosophy

Dirk Greimann

In his early philosophy, Quine defended his celebrated quantificational criterion of ontological commitment according to which a theory is committed to acknowledge the domain of its quantifiers. In his mature philosophy, he adopted a more liberal criterion according to which a theory can choose between various isomorphic domains that satisfy the logical structure of that theory. This structuralist criterion is based on a proxy-function argument according to which we can replace the domain of a theory by another domain without disturbing the logical structure or the empirical content of that theory. My aim in this paper is to show that the proxy-function argument does not really support the structuralist criterion. It rather entails that most sentences of our overall theory of the world are either false or neither true nor false. The reason is that the structural role of objects in theories does not provide the definite descriptions with a content that fulfills the uniqueness presupposition of the sentences in which they occur. This becomes evident when the proxy-function argument is compared with the parallel permutation argument in Frege’s system.