1. INTRODUCTION: HISTORICAL, METHODICAL, AND CONCEPTUAL FRAMES.- 2. THE OPERATION CALLED "VERSTEHEN" CONSIDERATIONS ABOUT FORMAL.- SYSTEMATIZATIONS OF UNDERSTANDING.- 3. MENTAL MODELS, THE GEOMETRY OF MEANING GENERATION AND OF INFORMATION.- 4. THE UNDERSTANDING OF LEARNING.- 5. THE HUMAN FACTOR: UNDERSTANDING HUMANS BY ARTIFICIAL SYSTEMS.- 6. CONCLUSIONS: AI AND A UNIFIED SCIENCE.- REFERENCES.