David Lewis
David Kellogg Lewis (September 28, 1941 – October 14, 2001) was an American philosopher who is best known for his metaphysical work in which he advocated a controversial modal realism - that is, he stated that the possible worlds that philosophers suppose in order to explain the nature of necessity and possibility exist in a concrete form. Lewis taught for most of his life at Princeton University, but also had a short stint teaching at the University of California at Los Angeles.
Lewis published five books: Convention: A Philosophical Study (1969), Counterfactuals (1973), Semantic Analysis: Essays Dedicated to Stig Kanger on His Fiftieth Birthday (1974) and On the Plurality of Worlds (1986) - which expounds Lewis' modal realism - and Parts of Classes (1991). He also published five essay collections - Philosophical Papers Volumes 1 and 2 (1983 and 1986 respectively), Papers in Philosophical Logic (1988), Papers in Metaphysics and Epistemology (1999) and Papers in Ethics and Social Philosophy.