The AGM Theory (Alchourrón, Gärdenfors, Makinson)

The AGM Theory, developed by Alchourrón, Gärdenfors, and Makinson, explains how rational belief sets change when we acquire new information. It outlines three key operations: expansion (adding new beliefs without removing anything), revision (integrating new beliefs while maintaining consistency), and contraction (removing some beliefs to resolve conflicts). The theory provides a formal framework to understand how beliefs can be consistently updated in response to new evidence, ensuring our knowledge remains coherent and rational over time.