The continuing relevance of Ludwik Fleck’s work, above its status as a classic in science studies, lies in his reflexive conceptualisation of an open epistemology. As early as 1929, in the midst of a broad debate about a ‘crisis’ of science, Fleck offered a socio-historical analysis of the widely assumed crisis in form of an epistemology. He presented his argument, which was in itself an interrogation of the metaphysical foundations of science, as a reflexive and political intervention to this debate. (...) His book of 1935, Genesis and development of a scientific fact, in which he developed the notion of the thought collective, can be read in a similar vein as a functional analysis of science under National Socialism. His traumatic experiences during this period fostered his drive for science, democracy and epistemology. When he returned to the epistemological debate in 1946, he sharpened the presentation of his argument, presenting it rhetorically as an ironic political dialogue. This surprising text unfolds as an epistemological intervention by a participant observer. In this respect, Fleck’s epistemology, combining the historical analysis with reflexive intervention, is still a message in a bottle. (shrink)