This paper critically examines the relation between problems and the formation and development of concepts in Bergson’s work, as well as in Bachelard, Canguilhem and Deleuze. Building on work by Elie During, I argue that it is not only Bergson but also Deleuze who shares with the French epistemological tradition an “anti-positivist” conception of concept formation, founded upon the posing and solving of novel problems as opposed to the acquisition and verification of empirical facts. Contrary to During, however, I argue (...) that it is not Bergson but Deleuze who furnishes us with an “anti-positivist” conception of problems that is adequate to this anti-positivist conception of concept formation. Deleuze’s anti-positivist view of problems holds, firstly, that genuine problems require the creation of novel terms in which to state and solve them. He shares this view with Bergson, Bachelard and Canguilhem. Secondly, however, Deleuze holds that a problem’s “truth” is not to be evaluated with reference to its eventual solutions, nor with reference to some privileged and contentful experience of reality, but is rather a matter of its purely intrinsic productivity. (shrink)