In the last chapter, Rein and Schon drew on theories of discourse and constructivism to enlighten policy issues. I want to turn to a seemingly more unlikely place to look for ideas about public policy – the philosophy of science. If it is true that scientific knowledge is common-sense knowledge ‘writ large’ (as Karl Popper constantly stresses), it is at least possible that students of public policy will find something worth learning in recent methodological debates among historians and philosophers of science. At any rate, this is the intriguing possibility that I explore in this chapter. More precisely, I argue that the conceptual models developed by Popper and Imre Lakatos to explain and appraise the growth of scientific knowledge are applicable (at least heuristically) to the study of policy development and to the practice of policy evaluation.

In recent years an increasing number of scholars have become convinced that public policy cannot be understood solely in terms of concepts like power, influence, interest, pressure, and decision. Ideas and arguments, far from being mere rationalizations or rhetorical embellishments, are integral parts of policy making (see also Weiss, chapter 14 in this volume); and policy development is always accompanied by a parallel process of conceptual innovation, debate, and persuasion. Thus, any adequate account of the evolution of public policy must take knowledge and ideas, as well as politics and economics, into consideration.