This paper investigates the relation between what James Conant has called Kantian and Cartesian varieties of skepticism. It is argued that a solution to the most prominent example of a Kantian variety of skepticism, i.e. Kripkensteinian skepticism about rule-following and meaning, can be found in the works of Wilfrid Sellars. It is then argued that, on the basis of that very same solution to the Kantian problematic of rule-following and meaning, a novel argument against external world skepticism can be formulated. (...) This argument takes the shape of a transcendental argument, which is reminiscent of Hilary Putnam’s infamous argument against the brain-in-a-vat hypothesis, but is, as is argued, superior to it in certain respects. (shrink)