In this paper we expose a new conception of ideology which is different from the sociological one, notably the one developped by Marx. As we know, Marx’s conception has several limits. The principal one is generally referred to as the Mannheim paradox. To avoid this difficulty, we propose a new conception of ideology based on cognitive specification of knowledge which distinguishes the major forms of learned discourse : the scientific, the philosophic and the ideological ones. These cognitive strategies of knowledge are called the pure forms of thought. The two main caracteristics of the ideological pure forms of thought are the followings : the first one is that the belief is (psycho)logically primary, its justification opportune ; the second one explicits an ontological principle deciding the essential articulation between two separate entities, man and society. This new approach of ideology allows us not only to forget about the Mannheim Paradox, but also to treat different applications in economic literature.
Since the beginning of the 1980’s, the hypothesis of hysteresis of the unemployment rate has met a great success. However, what this hypothesis means is not very clear. After having distinguished hysteresis and persistence, we propose an interpretation of the use of this physician’s term in economics. This project requires, on the one hand, to give up the popperian prohibition to study, from an epistemological point of view, the context of discovering ; it implies, on the other hand, to focus attention on the a priori of the economic discourse. We associate the importation of the hysteresis term with the recognition by the mainstream of a presupposion which has for a long time remained characteristic of the heterodox thought: the historical dependance of equilibrium.