The article shows the strategic analogies, but also the differences between Bachelard and Canguilhem on the use of the history of science for epistemology. It emphasizes the importance of the ideology for Canguilhem, and the conceptual essence he recognizes in the history of science, which is read in its internal specific differences and in its complex articulations with life and reality. No concept, in fact, comes from nothing. The link between history and epistemology is not however of subjection, but of mutual influence. Canguilhem radicalizes the thought of Bachelard, and recognizes the historicity of every aspect of scientific knowledge, even of its less valued features and above all of errors. All aspects of Science are historical. The object of the history of science is not the object of the sciences, because it is always a discourse. This is why the history of science is inevitably linked to other forms of history. This opens up a pluralist conception of History and of Time, thinking of the sciences in their real body and no longer ideal or legal. Thus Canguilhem opens the way to the researches of Foucault and Serres.
