Jean Baratgin is Professor of Cognitive Psychology and Epistemology at the University of Paris 8 (France). His main areas of research are rationality, uncertain reasoning, judgment, decision making, belief revision, cognition, human-computer interaction and experimental research. He defends the hypothesis that human beings spontaneously perform “probable reasoning” in uncertain situations but also in situations presented as certain. Probable reasoning would thus be the substratum of general human reasoning which would integrate all forms of reasoning (for example deduction and induction). He proposes subjective Bayesianism (founded by Bruno de Finetti) as a normative model for its theoretical qualities but also for its descriptive power.