Van een onzekere wetenschap naar een onzekere wereld

This thesis investigates how uncertainty in science impacts policy-makers and -- as a consequence -- their collective political decisions. Written from the standpoint of epistemology and philosophy of science, it focuses mainly on the epistemic consequences of uncertainty (i.e., its impact on individual and group beliefs) rather than its ethical ones (i.e., political consequences or moral values). After portraying a critique of the evidence-based policy-making account in policy science, this dissertation considers several aspects related to the daily practice of the scientists and policy-makers, such as the type of uncertainty they face, the way uncertainty is communicated from the scientists to the policy-makers, the time pressure of decision-making, the network of scientific interactions, and the bounded rationality of the agents. First, a philosophical understanding of the concept of uncertainty is articulated. After unveiling the evolution of this concept throughout the history of philosophy, the definition of scientific uncertainty is clarified. Eight types of uncertainty are examined: epistemic, ontic, conceptual, observational, underdetermination, information, replicability, and post-normal uncertainties. These types give the philosopher of science and the policy-maker an analytical tool to understand the features of the uncertainties they could face. Second, based on an interdisciplinary systematic literature review of experimental studies, the theories used to explain how policy-makers understand and respond to uncertainty communication are determined. The outcomes of this research reveal a prevalence of studies focusing on shallow uncertainty (quantifiable risk) and identify promising theories for future research on deeper (less quantifiable) uncertainties. Third, this thesis advocates for the use of agent-based modelling as a valuable method both in philosophy of science and in policy science. To strengthen this point, three agent-based models are implemented to study uncertainty's impact on policy-making. More precisely, they determine (a) the effects of timing in the communication of evidence on policy decisions, (b) the impact of scientific community structure, uncertainty, and bias on public understanding of science, and (c) a novel approach to the doctrinal paradox (also called discursive dilemma), considering a deliberative process in collective decision-making. In the field of philosophy, these results refine the integration of Bayesian epistemology into social epistemology thanks to a better understanding of individual and collective factors. In the field of policy science, the same results give a more acute understanding of the limitations of the evidence-based policy-making model. This thesis underscores the multifaceted nature of uncertainty in science and its significant impact on policy-making. By combining philosophical analysis, agent-based modeling, and interdisciplinary perspectives, the thesis provides valuable insights into the complex interplay between uncertainty, evidence, and political decisions. It also suggests insights for future research to deepen our understanding and improve the integration of uncertainty into policy processes.