AGM theory

AGM theory is a framework in belief revision that describes how rational agents should update their beliefs when new information arrives. It consists of three main operations: expansion (adding beliefs without removal), contraction (removing beliefs), and revision (adding new beliefs while maintaining consistency). The theory emphasizes minimal change—altering beliefs only as much as necessary—while ensuring the updated set remains logically coherent. Developed by Alchourrón, Gärdenfors, and Makinson, AGM provides a formal foundation for understanding rational belief updates, balancing new information with existing commitments to maintain a consistent and justified belief system.