At least since the beginning of the Western intellectual tradition, rationality has been widely regarded as a hallmark of human thinking. Rationality serves as a central standard by which we evaluate judgments, decisions, and beliefs. While theoretical frameworks have viewed rationality mostly as a solitary activity, more recent theoretical approaches have emphasized that human rationality is uniquely social. Humans reason, deliberate, and make decisions in interaction with others – exchanging views, discussing alternatives, and arguing from different standpoints. Motivated by this perspective, my research investigates rationality not only as an individual cognitive capacity but also as a fundamentally social phenomenon. To this end, my research has focused on three specific questions: (1) Do humans form, revise, and transmit beliefs in accordance with rational principles? (2) Do they seek information in rational ways? and (3) Do they attribute rational agency to others to predict and interpret behavior?

To investigate these questions, I take a diverse methodological approach and include participants from a multitude of age groups, cultures, and species in my research. I combine behavioral experiments, surveys, and interactive AI-based paradigms with eye tracking and functional near-infrared spectroscopy (fNIRS) to study rationality across development – from toddlers to adults. Theory-driven cross-cultural studies help me to distinguish universal from culture-specific strategies, while a comparative perspective with one of our closest great-ape relatives, chimpanzees, enables me to shed light on the evolutionary roots of human reasoning. By integrating diverse methods and perspectives, I aim to provide a comprehensive and ecologically valid account of human rationality.