The work presented in this thesis is concerned with the intimate relationship between human rationality and the consciousness of death. They jointly use two theories, that is, the terror management theory, and the dual-process theory of thinking. Terror management theory describes the mechanisms that are triggered when thoughts related to our own death are activated. Importantly, these mechanisms consume mental resources that the dual-process theory identifies as necessary for rational thought. Therefore, are we able to think rationally when thinking about our own death? In other words, can our analytical skills be efficiently used when thoughts of our own death are conscious? Are people with high cognitive abilities better equipped to think about death? What is the real impact of these thoughts on our reasoning, but also on our judgments and decisions? We seek to answer these questions in different areas of thought: logical inferences, strategic decisions, and moral judgment. Different experimental protocols are implemented in order to comprehensively explore the influence of thoughts of death while using these higher order cognitive functions. The results highlight grim, but fascinating effects on all our activities that require to mobilize cognitive resources. In general, participants who thought about their own death seem to no longer have access to their resources and therefore exhibit less elaborate behaviors, based on intuitions or heuristics, at the expense of normative rules of reasoning. These findings let appear a strange paradox in terms of evolution and adaptation because our analytical capacities finally seem to serve us to forget precisely what they made us discover.
