ABSTRACT
Conceptual change during scientific revolutions is a major issue in general philosophy of science and central to the work of Kuhn and all those who followed him, right up to the current work of Friedman and others, yet the significance of scientific revolutions has remained controversial. The dynamic theory of the a priori understands conceptual change in science as change in fundamental presuppositions that are required for the practice of science, a rather neglected idea until Friedman's work brought it back to life and under discussion. A pragmatic understanding of the constitutive elements in science should be seen as a deflationary strategy that leaves a core of beliefs about constitutive elements in place, but refuses to see them as supernatural or otherwise outside of the realm of science. Constitutive elements can function as what used to be called a priori knowledge even if they are no longer a priori in the traditional sense.
