In recent years, International Relations theorists have turned to philosophy in search of new ontological and epistemological foundations or to clarify their existing commitments. Scientific Realism and International Relations, edited by Jonathan Joseph and Colin Wight, is a good example of the former: editors and contributors make the case for Scientific Realism—a leading philosophy of science—in International Relations. Patrick Thaddeus Jackson, author of The conduct of inquiry in International Relations, is motivated by the latter concern, and devises a typology based on two key fissures among social scientists: the relationships between the knower and the known, and between knowledge and observation. The Joseph and Wight volume, while containing some thoughtful essays, does not convince the reviewer that assumptions that might apply in the physical world are relevant to its social counterpart. The Jackson book is an intellectual tour de force and a compelling plea for pluralism.