RESUMEN
Ideational scholarship, as this volume proves, is alive and well in political science, sociology, and political economy. The proposition that ‘ideas matter’ for explaining outcomes is now well established. What is less established is why, where, and how we know they matter? This essay attempts to answer these questions by giving reasons for why they matter (issues of probability and variance in a given environment) and how they matter (issues of ontology and epistemology). Drawing on work in uncertainty and probability, as well as evolutionary theory, I demonstrate that the way the social world is put together necessitates an engagement with ideas at a fundamental level, because without them, neither stability nor change in social systems can be fully understood. Given this understanding, the conditions under which ideas matter becomes a much more tractable proposition; one that necessitates that all social scientists take ideas very seriously indeed.