His first book was on Bertrand Russell (Routledge, 1979). His most recent book, Fiction and Fictionalism (Routledge, 2009) concerns the semantic and ontological status of fictions. Reference Without Referents (Oxford, 2005), is on the semantics of referring expressions. His book Departing From Frege (2002) is on the philosophy of Gottlob Frege. He has also written about paradoxes (Paradoxes Cambridge, 1988, 1995, and Tolerating Vagueness, published in the Proceedings of the Aristotelian Society, 1989-9).