 In this, p is known apriori (or just: “p is apriori”) iff p is known without a concerted empirical investigation of the external world. (Note that introspective knowledge counts as “apriori” in this context, even though it arises from a kind of introspective experience. For more on the present conception of the apriori, see Miller 1997, Davies 1998, Nuccetelli 1999, and McLaughlin 2000; 2003). On the current line, (1) can be known apriori if EXT is true (though as we shall see, there are different ways to spin this). Whereas, (2) is apriori given SK. Yet if Oscar has apriori knowledge of both (1) and (2), Oscar can then use modus ponens to know apriori that: