The idea that policy should be based on best research evidence might appear to be self-evident. But a closer analysis reveals a number of problems and paradoxes inherent in the concept of "evidence-based policymaking." The current conflict over evidence-based policymaking parallels a long-standing "paradigm war" in social research between positivist, interpretivist, and critical approaches. This article draws from this debate in order to inform the discussions over the appropriateness of evidence- based policymaking and the related question of what is the nature of policymaking. The positivist, empiricist worldview that underpins the theory and practice of evidence-based medicine (EBM) fails to address key elements of the policymaking process. In particular, a narrowly "evidence-based" framing of policymaking is inherently unable to explore the complex, context-dependent, and value-laden way in which competing options are negotiated by individuals and interest groups. Sociolinguistic tools such as argumentation theory offer opportunities for developing richer theories about how policymaking happens. Such tools also have potential practical application in the policymaking process: by enhancing participants' awareness of their own values and those of others, the quality of the collective deliberation that lies at the heart of policymaking may itself improve.