I: Hoffding as Mentor.- I.- 1. Harald Hoffding, His Life and Thought.- 2. Hoffding and Bohr Senior.- II.- 1. The Ekliptika Circle.- 2. Bohr and William James.- 3. Bohr and Kierkegaard.- 4. The Student Bohr on Formal Logic.- III.- 1. The Friendship.- 2. The Years Around 1927.- 3. Hoffding on Complementarity.- IV.- 1. Hoffding's Theory of Knowledge.- 2. Totality as a Category.- 3. Hoffding's Philosophy of Mind and Psychology of Free Will.- 4. Hoffding on Biology.- 5. Analogy and Scientific Progress.- II: Bohr and the Atomic Description of Nature.- V.- 1. The Principle of Correspondence.- 2. The Search for an Interpretation.- VI.- 1. Complementarity.- 2. Quantum Mechanics and Psychology.- 3. Bohr on Biology.- VII.- 1. The Objectivity of Knowledge.- 2. The EPR Discussion.- 3. The Conditions for Description.- VIII.- 1. Bohr and Realism.- 2. Hoffding on Reality.- 3. Objective Anti-Realism.- Epilogue: The Legacy.- Notes.