This article seeks to provide a systematic reconstruction of the hermeneutic motifs in Ludwik Fleck’s social epistemology and comparative cognitive sociology. The exegetical analysis of his work is extended and complemented by a hermeneutic critique of Fleck’s psychologism. I begin with the recognition that Fleck’s theory of the constitution of scientific facts involves a distinction between phenomena and observable facts. This distinction is underdeveloped in his book, but it plays a central role in his scientific papers. After discussing Fleck’s constitutional theory by putting emphasis upon the historicity of scientific facts, I provide a rationale for the claim that the kind of sociality he attributes to the thought collectives is closer to the concept of interpretive trans-subjectivity rather than normative inter-subjectivity. To this sociality corresponds a concept of thought style as an open horizon of interpretation. By approaching the way in which such a horizon reveals and conceals a field of investigation, I finally discuss Fleck’s concept of the “event of truth.” The thesis is advocated that Fleck is not an adherent, but rather an opponent of social constructivism as it has been understood in the last half century.