Translators' Introduction: A Guide for Psychologists, PART I The Development of Propositional Logic 1. The Equality of Angles of Incidence and Reflection the Operations of Reciprocal Implication 2. The Law of Floating Bodies and the Elimination of Contradictions 3· Flexibility and the Operations Mediating the Separation of Variables 4· The Oscillation of a Pendulum and the Operations of Exclusion 5· Falling Bodies on an Inclined Plane and Operations of Disjunction 6. The Role of Invisible Magnetization and the Sixteen Binary Propositional Operations 93 PART II The Operational Schemata of Formal Logic 7· Combinations of Colored and Colorless Chemical Bodies 8. The Conservation of Motion in a Horizontal Plane 9. Communicating Vessels 10. Equilibrium in the Hydraulic Press 11. Equilibrium in the Balance 12. Hauling Weight on an Inclined Plane 13· The Projection of Shadows 14· Centrifugal Force and Compensations 15· Probable Dispersions and Correlations PART III The Structural Integration of Formal Thought 16. Formal Thought from the Equilibrium Standpoint 17. Concrete and Formal Structures 18. Adolescent Thinking