Abstract
This book is an introduction to the Free Energy Principle (FEP) and Active Inference. The FEP has been described as new paradigm with potential to unify the biological and cognitive sciences. According to the FEP, living organisms persist by minimizing their free energy (which can be variously translated as uncertainty, surprise, prediction error, or discrepancies between model and world). Active Inference means that we can resolve uncertainty (or discrepancies between model and world) in basically two ways: by perception (i.e., changing our mind to fit the world) and by action (i.e., changing the world to make it fit our preferences and beliefs). The FEP and Active Inference represent a conceptual framework that may have potential to contribute to a unification of psychological science.