There are periods in the history of human thought which are characterized by an extraordinary concentration of creativity. Such periods are to be found in antiquity as well as in modern times. At the end of the eighteenth and the beginning of the nineteenth centuries, in the span of one generation between the appearance of Kant's Critique of Pure Reason in 1781 and the subsequent development of the systems of thought known as the philosophy of identity (Fichte, Schelling and Hegel), there evolved an array of systematic world conceptions which are distinguished by their scope and comprehensiveness. Kant was the first to attempt a revolution in human thought, his own Copernican revolution. Once this revolution got under way, however, it did not stop in the realm of critical thought, but swept on, begetting a variety of metaphysical conceptions far beyond Kant's original intention.