Since the early days of economics, the rationality principle has been a core element of economic theorizing. It is part of almost any theoretical framework that economists use to generate knowledge. Despite its central role, the principle’s epistemic status and function continue to be debated between empiricists and rationalists, and a clear winner is yet to emerge. One point of contention is that we cannot explain the principle’s special status in light of clear evidence against its empirical validity and the continuous conceptual changes it undergoes. In this paper, I argue that we should think of the rationality principle as a functional a priori principle along the lines of a pragmatic theory of constitutive elements recently put forward by David Stump. Such an approach would explain the principle’s persistence and changing status. More generally, the pragmatic theory of constitutive elements in science offers a viable alternative to rationalism and empiricism that allows for approaching the debate about the status and function of the rationality principle in economics. It provides a new framework and starting point to think about the usefulness of a central first principle in economics in a constructive way.