Problems about the relations between Leibniz's philosophy and his logic have exercised scholars ever since Bertrand Russell's book on the philosophy of Leibniz, first published in 1900. The thesis of that book, as Russell expressed it later, was that “Leibniz's philosophy was almost entirely derived from his logic.” Russell's argument was that Leibniz derived from his logic his distinctive views about the nature of substance - that each substance is a genuine unity, a “monad”; that each created substance expresses the entire universe, and, strictly speaking, does not act on any other substance; that each substance is a soul, or at any rate soul-like; and that no substance resembles any other substance entirely. Russell also discussed Leibniz's views about contingency, about possible worlds, and about freedom. In this volume, Leibniz's views about logic and substance are discussed by Professor Sleigh in a separate chapter; I shall restrict myself to the topics of contingency, possible worlds, and freedom. This is not a haphazard group; there are close connections between Leibniz's discussions of these topics. Nor are the issues raised merely marginal; on the contrary, they take us to the very heart of Leibniz's philosophy.