Consider one form of skeptical argument upon which leading contextualists have focused (e.g., Cohen 1986, 1988, 2014; DeRose 1995; Neta 2003a &amp; b; cf. Unger 1975). (We can call it ‘SA’, for ‘skeptical argument’.) Let ‘h’ stand for some skeptical hypothesis, e.g., that I am a mere brain in a vat of brain nutrients being stimulated to have just those experiences that I have had. Let ‘p’ stand for a mundane external world belief that I seem to know, e.g., that I have hands. Here is the argument: