Warfield can justify a priori knowledge of premise 1 by virtue of the principle that one can always have a priori knowledge of the contents of one's own thoughts

Warfield suggests that one major advantage of his argument (W) is that it appears to avoid the charge of question-begging that (as we’ve seen) is so often made against other forms of Putnamian anti-skeptical argument. (A similar motivation is also suggested by Brueckner 2016: 5.) This is because, Warfield says, he can justify a claim to have a priori knowledge of both of the argument’s premises: premise 2 on the basis of externalist thought experiments by Putnam and others; premise 1 by virtue o