 Crathorn had to face up to the skeptical consequences of this odd epistemology. How can we know what is real if our only access to reality is via representations of its qualitative features? His answer to this question is quite radical: we cannot be naturally and directly certain that reality exists as we conceive it since it is not possible to distinguish qualities inside and outside the mind: as qualities, they would have precisely the same nature (ibid. concl. 10–13). The only solution to skeptical doubt here is the principle, which he claims is known per se, that God does not produce an effect supernaturally in order to lie or to lead people into error (ibid. q. 1, concl. 14), a principle more famously used in connection with Descartes’ thought experiment of a Dieu trompeur several centuries later.