It presents a profound and challenging investigation into the nature of human reason, its knowledge and its illusions. Reason, Kant argues, is the seat of certain concepts that precede experience and make it possible, but we are not therefore entitled to draw conclusions about the natural world from these concepts. The Critique brings together the two opposing schools of philosophy: rationalism, which grounds all our knowledge in reason, and empiricism, which traces all our knowledge to experience. Kant's transcendental idealism indicates a third way that goes far beyond these alternatives.