The paper reviews the historical origins of the current split between different forms of reflection on science, in particular between normative philosophical positions and descriptive historical positions that consider science as embedded in society and culture. It analyzes the historical and intellectual contexts in which this split emerged in the early part of the twentieth century, taking the philosopher Moritz Schlick and the scientist and historian Ludwik Fleck as main reference points. The history of Einstein’s general theory of relativity and its new understanding of space and time is analyzed in relation to these positions. The paper follows the split between the different forms of reflection through further developments in the philosophy and history of science, discussing the views of Otto Neurath, Rudolf Carnap, Martin Heidegger, and Thomas Kuhn, among others. It suggests that current debates on historical epistemology could benefit from taking the split of rationality—inherited from the catastrophic twentieth century—as a challenge to be addressed by an integrative historical theory of knowledge development.