(Ph.D., University of Washington). He has published many articles in his principal areas of interest: philosophy of mathematics and philosophy of logic. He has also published widely in the philosophy of science and confirmation theory, as well as on the philosophies of Wittgenstein, Russell, Quine, Goodman and Davidson. He is the author of Ontology and the Vicious Circle Principle (1973), Constructibility and Mathematical Existence (1990), The Worlds of Possibility: Model Realism and the Semantics of Modal Logic (1998), and A Structural Account of Mathematics (2004). He is now working on various problems in the philosophy of mathematics.