The Split of Rationality

The Split of Rationality

Olaf Engler, Jürgen Renn

Cooperation Partners: 

Center for Logic, History and Philosophy of Science, University of Rostock


Ludwik Fleck (1896-1961), the Vienna Circle’s first important critic © Archives for contemporary history, ETH Zurich


Moritz Schlick (1882-1936), the founder and leading figure of the Vienna Circle, in 1934. © George Moritz H. van de

Since the beginning of the twentieth century, reflection on science tended to be separated into four branches: a philosophical-normative branch, a historical-descriptive branch, a political-pragmatic branch, and a anthropological-ontological branch. The result was a split of rationality, largely separating science from a reflection referring to its contents as well as to its contexts and societal conditions. In the framework of the project, origins and developments concerning this split of rationality are being investigated.  

Whereas philosophy of science was dominated by a focus on the analysis of language and methodology, taking them as embodiments of an ahistorical scientific rationality, history of science paid attention to ideas, events, and their more or less contingent circumstances, without critically examining the underlying normative rationality, let alone substituting it with its own form of historical rationality.

By the middle of the 1930s, philosophers of science such as Rudolf Carnap, but also Moritz Schlick under the influence of Ludwig Wittgenstein, had retreated toward the logical analysis of language. The split of rationality represented by this retreat becomes particularly evident in the episode recounted in the following, the brief written encounter between Schlick and the Vienna Circle’s first important critic, the Polish bacteriologist, doctor and historian of science Ludwik Fleck.

From a modern perspective, this encounter strikingly anticipates the far-reaching conflicts between different perspectives on science, as they would come to determine the discourse throughout the following decades up until the present day. And yet, at the same time, what becomes evident in this encounter is the willingness to continue the dialogue and, in the situation of a political crisis rapidly coming to a head, the eagerness not to abandon the common battle for scientific rationality, even in the face of widely diverging criteria for science.


  • F.O.Engler und J.Renn, Krumme Wege der Vernunft, Frankfurter Allgemeine Sonntagszeitung, 5. Juni 2011, Nr. 22, 62 f.
  • F.O.Engler, Koinzidenzen, Gestalten und Denkstile. Moritz Schlick und Ludwik Fleck über die Objektivität am Fundament der Erkenntnis und die Bedeutung der Wissenschaftsgeschichte. In: Moritz Schlick. Ursprünge und Entwicklungen seines Denkens. F.O.Engler und M.Iven (Hrsg.). Berlin, Parerga 2010, 339-386.