This article constitutes an updating of a work about complexity, which becomes more precise and little by little more complete (1999, 2003, 2018b in particular). One of the basic ideas is that modelisation of society functioning is a three-stage (three ―moments―) scheme (institutional theory), on condition that the third stage (moment) comes back on the first one in a loop, it describes the dynamic movement of an autopoietic system (cf. Varela). Thus, the strange autopoietic loops proposed by Varela can be adapted to the modelisation of society, enriching the idea of co-generating elements and shape (Barel and Castoriadis), which is characteristic of complexity, according to Castoriadis. Traditionally in Physics, we characterize a size before stating its definition (making the sides of a notion more precise before it becomes a concept). We will begin with mentioning Le Moigne and Morin’s work on characterization. Then, we will study Nicolis and Prigogine’s propositions, and finally Castoriadis’s work. We will continue with the coming up of strange autopoietic loops. For the discussion, we will finally come to the matter of the link drawn between unvarying element and concept (Vergnaud) applied to complexity.