Acknowledgements -- Introduction -- Chapter One: Aristotle on Division -- Plato on collection and division -- Aristotle on collection and division -- What is the object of definition by division? -- Problems -- Chapter Two: The Four Types of Definition -- Two objects of definition -- What is it to have something else as an aition? -- Simple objects and immediate definitions -- Conclusion -- Chapter Three: Definitions and Aitia -- Aitia and the structure of syllogistic and immediate definitions -- Why and how definitions with aitia are necessary -- Conclusion -- Chapter Four: Definition and its Object in the Metaphysics -- The problem of compounds and coupled items -- The unity of the definable form and of the definition -- Matter in the definable form -- Definitions and definable essences as universals -- Conclusion -- Chapter Five: Stating the Essence in the Topics -- Questions from the Metaphysics and the Posterior Analytics -- Can the Topics concern metaphysics or science? -- The Topics and definition -- Stating the essence in the Topics -- How the Topics answers the questions -- Two problems -- Conclusion -- Bibliography -- Index Locorum -- General Index.