**1. Introduction**

Since psychology has set as its main purpose the study of behaviour, decisionmaking behaviour represents a stimulating subject for studies and research. Not only are there numerous circumstances in which it proves necessary to make a choice, but they are also highly varied. This chapter analyses a quite specific category of decisions: those concerning the action choices in complex and dynamic systems. Highly different from other decisions studied in fixed environments,

they lead us to explore the field of epistemology and cognitive psychology and offer the advantage of generating sensitive crossed interrogations in these two disciplines also required for the construction of knowledge.

This chapter will focus on one of these, in other words the relations between the choice of an objective epistemology and the absence, observed in the field, of relevant decisions. The argument has seven facets. The first describes the cognitive and epistemological specificities of decision-making in complex and dynamic systems. The second deals with the assignment of meaning to information, while the third describes a selection of real situations which led to decision-making difficulties. The fourth facet is dedicated to the examination of an investigation tool: the paradigm, and refers to a particular paradigm; the objective experimental paradigm (OEP) which underlies scientific progress in numerous disciplines. The fifth facet focuses on its transferability to decision-making in complex and dynamic systems and any resulting cognitive dilemmas. The sixth facet raises the question of the globality of the situations to be processed (rather than their breakdown into variables) by taking as guideline an attempt made to this effect in psychology. The seventh examines the epistemological position of the decision-makers faced with a paradox which seems to be related to valorisation at all costs of objectivation, at the expense of other characteristics of the decision.
