The Structure of Scientific Revolutions represented a milestone in the attempt to understand scientific development based on empirical observations. However, in the next decades after the publication of his book, history, psychology, and sociology became increasingly marginal in Kuhn’s discussions. In his last articles, Kuhn even suggested that philosophers should pay less attention to empirical data and focus more on “first principles.” The purpose of this article is, first, to describe this radical transformation in Kuhn’s methodological approach, from his initial (...) naturalism to his later and more strict philosophical stance. Next, I present some of the alleged justifications for explaining this transition, such as his interest in problems more firmly attached to the philosophical tradition and a desire for greater acceptance within this community. Although these factors certainly played a role in explaining Kuhn’s change, I also believe that an important theoretical component exerts a fundamental function in this transition: the idea that scientific development is a kind of evolutionary process, which is better understood through the use of abstract theoretical models, instead of sparse observations of scientific activity. (shrink)