Metaphysics is usually taken to be that part of analytical philosophy which offers an account of the most basic and persuasive concepts we use, an inventory and analysis of such fundamental structural features of our world as existence, substance, change and quality. But there is a revisionary as well as a descriptive metaphysics. Some philosophers and theologians have sought to reach beyond these familiar conceptual categories and to extend the scope of human understanding and language. What sort of an intellectual enterprise would that be, and what sort of facts, truths or understanding could it yield? Professor MacKinnon devotes this book to a study of these questions - the nature and possibility of a revisionary metaphysics.