Realizing Reason pursues three interrelated themes. First, it traces the essential moments in the historical unfolding--from the ancient Greeks, through Descartes, Kant, and developments in the nineteenth century, to the present--that culminates in the realization of pure reason as a power of knowing. Second, it provides a cogent account of mathematical practice as a mode of inquiry into objective truth. And finally, it develops and defends a new conception of our being in the world, one that builds on and transforms the now standard conception according to which our experience of reality arises out of brain activity due, in part, to merely causal impacts on our sense organs.