Instituting inconsistency.

Summary How can we understand that at the heart of the mathematical tools used daily by financial actors is the assimilation of two situations - situations of randomness and heterogeneity - that statistical tools very unequally allow to grasp? The article traces the way in which the amalgam between situations of randomness and situations of heterogeneity comes to play the role of an institution within the insurance sector, distinguishing, within this process of institutionalization, the moments of underground appropriation and the times of mobilization. The amalgam was first slowly appropriated by financial market and banking professionals, and it was from these activities, which were contiguous to it, that it entered the insurance sector. Two episodes of mobilization were then decisive, one concerning the valuation of companies involved in merger-acquisition operations, the other concerning the implementation of new prudential rules. It was then reintroduced as an institution in the practice of the actors, who sometimes adhered to it unconditionally, and sometimes maintained a reflexive distance from it.