The phenomenon of human knowledge is no doubt the greatest miracle in our universe. It constitutes a problem that will not soon be solved, and I am far from thinking that the preset volume makes even a small contribution to its solution. But I hope that I have helped to restart a discussion which for three centuries has been bogged down in preliminaries.
Since Descartes, Hobbes, Locke, and their school, which includes not only David Hume but also Thomas Reid, the theory of human knowledge has been largely subjectivist: knowledge has been regarded as a specially secure kind of human belief, and scientific knowledge as a specially secure kind of human knowledge.
The essays in this book break with a tradition that can be traced back to Aristotle—the tradition of this commonsense theory of knowledge. I am a great admirer of common sense which, I assert, is essentially selfcritical. But while I am prepared to uphold to the last the essential truth of commonsense realism, I regard the commonsense theory of knowledge as a subjectivist blunder. This blunder has dominated Western philosophy. I have made an attempt to eradicate it, and to replace it by an objective theory of essentially conjectural knowledge. This may be a bold claim but I do not apologize for it. [Preface]