PREFACE -- CONTENTS -- I. Introduction: the Study of the History of Ideas -- II. The Genesis of the Idea in Greek Philosophy: the Three Principles -- III. The Chain of Being and Some Internal Conflicts in Medieval Thought -- IV. The Principle of Plenitude and the New Cosmography -- V. Plenitude and Sufficient Reason in Leibniz and Spinoza -- VI. The Chain of Being in Eighteenth-Century Thought, and Man's Place and Rôle in Nature -- VII. The Principle of Plenitude and Eighteenth-Century Optimism -- VIII. The Chain of Being and Some Aspects of Eighteenth-Century Biology -- IX. The Temporalizing of the Chain of Being -- X. Romanticism and the Principle of Plenitude -- XI. The Outcome of the History and Its Moral -- Notes -- Index of Names and Subjects.