 One might respond (cf. Stanley 2011b) to this regress challenge that the student does not really understand the premises of an argument by modus ponens (p, if p then q), for that involves grasping the concept of a conditional, and on an inferentialist understanding (Boghossian 1996, 2003), that would dispose one to accept the conclusion of an inference by that rule. Inferentialism about meaning is, however, a controversial doctrine (for several criticisms, see Williamson 2011, 2012). Other replies might be available. Maybe the student does not represent the rule practically (see next section), or she is simply incapable of granting that the rule applies to this case, for that would explain her failure to be appropriately disposed to arrive at the conclusion, given the truth of the premises. (For yet other versions of the regress challenge, see Noë 2005: 285–6 and Hetherington 2006).