1. Gustav Bergmann, “A Note on Ontology”, Philosophical Studies 1 89–92, (1950).
2. Paul Bernays, Uber eine natürliche Erweiterung des Relationenkalküls, in Constructibility in Mathematics, ( A. Heyting, ed.), North-Holland, Publishing Co., 1959, pp. 1–14.
3. Rudolf Carnap, Empiricism, Semantics, and Ontology, Revue Internationale de Philosophie 11, 20–40, (1950). Reprinted in Meaning and Necessity, 2d ed., University of Chicago, 1956.
4. Rudolf Carnap, Replies and Systematic Exposition, in The Philosophy of Rudolf Carnap (P. A. Schilpp, ed.), Open Court, La Salle, 1963, pp. 859–1013, specifically p. 868.
5. Alonzo Church, “Ontological Commitment”, Journal of Philosophy
55, 1008–1014, (1958).