Semantic Pragmatism and A Priori Knawledge (or ‘Yes we could all be brains in a vat’)

Abstract

Hilary Putnam has famously argued that we can know that we are not brains in a vat because the hypothesis that we are is self-refuting. While Putnam's argument has generated interest primarily as a novel response to skepticism, he originally introduced his brain in a vat scenario to help illustrate a point about the ‘mind/world relationship.’ In particular, he intended it to be part of an argument against the coherence of metaphysical realism, and thus to be part of a defense of his conception of truth as idealized rational acceptability. Putnam's discussion has already inspired a substantial body of criticism, but it will be argued here that these criticisms fail to capture the central problem with his argument. Indeed, it will be shown that, rather than simply following from his semantic externalism, Putnam's conclusions about the self-refuting character of the brain in a vat hypothesis are actually out of line with central and plausible aspects of his own account of the relationship between our minds and the world.