1. Metaphysical Realists have traditionally relied upon the skeptic to give substance to the idea that truth is, in the words of Hilary Putnam, 'radically non-episternic,’ forever outstripping, in principle at least, the reach of justification. What better model of truth so conceived, after all, than the skeptic's contention that even our firmest convictions might be mistaken in that we might be the victims of demonic deception or the machinations of an evil scientist? But the availability of this favorite model of Realist truth, encapsulated in the claim that we might be ‘brains in a vat,’ has been called into question by Putnam in the opening chapter of Reason, Truth, and History. Putnam contends that, if we grant the Realist notion of truth, as referentially mediated correspondence to THE WORLD, then, given certain plausible constraints on reference, we can know that we are not brains in a vat (or, more accurately, ‘brains in a vat' of a particular kind, as we shall see).