1. Decision analysis and complexity

Work on the complex and on systems today represents an alternative approach to the positivism so attached to determinism and the continuity of processes. Against the backdrop of the multiplicity of fields involved, and the general consensus on the importance of the problem, we are witnessing a multiplication of new concepts and a linguistic polymorphism that makes communication and understanding of emerging approaches all the more difficult.

Depending on the approach taken, the concept of complexity today has multiple meanings:

• a phenomenon is perceived as complex when the perception of its complication exceeds a certain threshold; in this sense, the "very complicated" would become complex;

• a phenomenon whose representations are perceived not to be reducible to a single model, however...