 In response, a defender of SK may concede that there is a “training period” for acquiring a concept. Still, apriori knowledge might be possible in that, once the subject has acquired the relevant concepts, she can use them to gain new knowledge without further empirical inquiry (Boghossian &amp; Peacocke 2000, p. 2). But one problem is that EXT usually portrays concept possession in a way that blurs the distinction between the “training phase” and the post-acquisition phase (Hawthorne 2007, p. 213). For the externalist thought experiments allow a subject to possess (e.g.) the sofa concept even prior to being “trained” that no armchair is a  sofa.[19] 