Does Putnam's Argument Beg the Question against the Skeptic? Bad News for Radical Skepticism

摘要

The most convincing – and shortest – version of Putnam's argument against thepossibility of our eternal envattment is due toCrispin Wright (1994). It avoids most of themisunderstandings that have been elicited byPutnam's original presentation of the argumentin Reason, Truth and History (1981).But it is still open to the charge ofquestion-begging. True enough, the premisses ofthe argument (disquotation and externalism) canbe formulated and defended without presupposingexternal objects whose existence appearsdoubtful in the light of the very skepticalscenario which Putnam wants to repudiate.However, the argument is only valid if we add anextra premiss as to the existence of some external objects. In order to avoidcircularity, we should run the argument withexternal objects which must exist even if we arebrains in a vat, e.g. with computers rather thanwith trees. As long as the skeptic is engaged ina discussion of the brain-in-a-vat scenario, sheshould neither deny the existence of computersnor the existence of causal relations; for ifshe does, she is in fact denying that we arebrains in a vat.