 A rather different line against SK derives from an externalist view about concept possession. This view hypothesizes that possession of a (non-empty) kind concept requires the ability to ostend or demonstratively identify instances of the kind by perceptual means (Brewer 1999; 2000a; 2000b). If so, then to possess the water concept is already to know perceptually where (instances of) the stuff resides. That in turn normally suffices for knowing that water exists. So when it comes to the reductio, the absurdity stems from thinking that (2) is apriori, since knowledge of (2) already rests on knowledge of (3). So one can hardly learn (3) for the first time via knowledge of (2)—the learning proceeds in the other direction.