Can philosophical concepts do real work in improving our world? Should we, when evaluating competing understandings of concepts like 'justice' and 'solidarity,' take into account whether these different understandings can actually help us to fight injustice and promote solidarity between people? The Fruitfulness of Normative Concepts is the first book-length attempt to argue that the answer to both of these questions is an emphatic “yes.” In doing so, it provides a bold new defense of a tight relationship between theory and practice. Drawing on cutting-edge scientific research, the book also demonstrates that we now have the tools to evaluate the practical value of normative concepts.Moral and political philosophers should be and have often been, explicitly or implicitly, interested in a number of dimensions of fruitfulness that Matthew Lindauer delineates, and it is an empirical question whether a given concept is fruitful in these ways. These dimensions of fruitfulness include the extent to which moral and political concepts (i) motivate the right kinds of behavior when internalized (Motivational Fruitfulness), (ii) prevent the wrong kinds of behavior (Prevention Fruitfulness), (iii) help us fight back against problematic social phenomena such as bias and discrimination (Resilience Fruitfulness), (iv) are capable of achieving consensus to a sufficient extent among people committed to cooperation and peaceful coexistence (Consensus Fruitfulness), and (v) can serve as useful guides in solving practical problems that we need to solve (Guidance Fruitfulness). Lindauer's research establishes that, rather than merely clearing the way for philosophical work to be done, empirical research is an important part of the philosophical enterprise, is continuous with traditional a priori research methods, and will be required to resolve at least some important debates in moral and political philosophy.