Putnam’s vat argument is intended to show that I am not a permanently envatted brain. The argument holds promise as a response to vat scepticism, which depends on the claim that I do not know that I am not a permanently envatted brain. However, there is a widespread idea that the vat argument cannot fulfil this promise, because to employ the argument as a response to vat scepticism I would have to make assumptions about the content of the premises and/or conclusion of the argument that beg the question against the sceptic. In this paper, I show that this idea is mistaken.
Thanks to Crispin Wright, Peter Sullivan, Adrian Haddock, David Horst and Bernhard Salow for helpful discussion. This paper benefited greatly from being presented at a Philosophy Work in Progress Seminar at the University of Campinas, a Knowledge Beyond Natural Science Project Seminar at Stirling University, and a Philosophy of Language Group Seminar at Edinburgh University. I would like to thank all three audiences for their comments. An anonymous referee at Philosophical Studies also provided comments which have greatly improved the paper. I am grateful for a research grant from the São Paulo Research Foundation (Grant ID No. 2016/03277-1) that allowed me to complete this paper.