‘‘Complexity,’’ in science, can be linked to the need of using, in parallel, not reducible models (= the coexistence of non-equivalent descriptive domains required) for a useful representation of a certain phenomenon. This is always the case, when dealing with: (1) nested hierarchical systems in which relevant patterns are detectable only on different space-time scales; and (2) socioeconomic systems in which agents are not only non-equivalent observers, but also reflexive.
