3 - How to think about whether we are brains in vats

Summary

Imagine that duplicates of our brains are in a vat from the beginning to the end of their lives, stimulated by a computer in exactly the same way that our brains are stimulated, and that both the duplicate brains and the computer came into existence by quantum accident. Call these “brains that are always in a vat.” I assume it is at least physically possible that there be such brains. This physical possibility becomes philosophically interesting when we find ourselves tempted to think that, despite our ordinary beliefs to the contrary, we may actually be brains that are always in a vat.

In Chapter 1 of Reason, Truth, and History, Putnam argues that even if it is physically possible that there be brains that are always in a vat, it cannot actually be true that we are always brains in a vat. The best-known reconstructions of Putnam's argument assume that its goal is – and ought to be – to rule out by strictly a priori reasoning the supposedly coherent possibility that we are always brains in a vat. Against this, I will argue that the goal of Putnam's argument is to dissolve a problem that apparently arises from within his own non-skeptical account of the methodology of inquiry. To motivate my non-standard reconstruction of Putnam's argument, I begin by reviewing some of the problems that standard reconstructions of it face.

Problems for standard reconstructions

What is the goal of Putnam's argument? Standard reconstructions of it assume

Answer 1: The goal of Putnam's argument is to show, by strictly a priori methods, that we are not always brains in vats.

Answer 1 implies:

(A) Putnam's argument is successful only if a person who is agnostic about whether he or she is always a brain in a vat can reasonably accept all of its premises.

As Crispin Wright explains, “… the argument, if sound, should have the power to move an agnostic to the conclusion that he or she is not a brain in a vat” (Wright 1994: 222). Similarly, according to Anthony Brueckner, “that I am a normal human being speaking English rather than a BIV speaking vat- English … must be shown by an anti-skeptical argument, not assumed in advance” (Brueckner 1986: 160).