What is irrationality? Gigerenzer (2025) reflected upon the "rationality wars" that have defined his scientific career and suggested three competing paradigms: logical rationality, the cognitive biases program, and ecological rationality. Certain human behaviours are irrational under all three definitions, and I operationalise these phenomena as "implausible belief updating". This bundle of behaviours includes the optimism bias, perverse belief disconfirmation effects, and the "actual stock of [implausible] beliefs" (Mandelbaum, 2020) that millions of people confidently hold. So why do people engage in implausible belief updating? There are two main theories: a) the influence of expectations ("cold" cognition; confirmation bias), and b) the influence of motivations ("hot" cognition; desirability bias/wishful thinking). Recent work has shown that "cold" accounts, while powerful, are inadequate: "hot" wishful thinking is uniquely implicated in implausible belief updating. Why then does wishful thinking occur? There are four main theories: self-deception, cognitive dissonance, motivated reasoning, and psychological immune neglect. In my own work I have discarded self-deception, and have found the other three explanations to be useful but inadequate. In this presentation I will introduce my own theory of wishful thinking (doubt aversion theory), designed to build upon these previous models and better explain irrationality.
