Sociologists, economists, historians, anthropologists, political theorists, and literary critics have all turned their attention to the study of capitalism. But philosophers remain much less engaged. Why is this? And what could philosophy bring to the study of capitalism? Could it help in the development of a general theory? My main argument here is that philosophy does have an important role to play in the study of capitalism, particularly if we want to develop a general theory. Philosophers must describe something that is peculiar to capitalism, in philosophical terms, which has not been explained by sociological, economic, or psychological means. This subject matter does exist: it is the nature of rationality within capitalism. I suggest that this can best be explained by using the theory of the space of reasons, which helps to show how rational human practices shape social and economic institutions, and how our form of rationality is in turn shaped by those practices and institutions.