In his 1999 paper "How to Defeat Opposition to Moore", Ernest Sosa argues that sceptical, Nozickian tracking, relevant-alternative, and contextualist accounts of the sceptical paradox rely on the notion of sensitivity. A belief is is sensitive if and only if it would not be held if it were false, i.e. ~p → ~B(p). According to Sosa, the sensitivity requirement posited by these accounts is problematic because, among other things, it leads to an "abominable" conjunction:
- (h) I am a handless brain in a vat being fed experiences as if I were normally embodied and situated.
- (o) I now have hands.
One's belief that O is sensitive because if it were not true that one had hands, one would not believe that one had hands. Moreover, O entails not-H. However, one's belief that not-H cannot be sensitive because even if one were, in fact, handlessly envatted, one would believe that one were not.
Sosa proposes that instead of sensitivity, safety should should be required. A belief is safe if and only if it would only be held only if it were true, i.e. B(p) → p. (Safety is not equivalent to sensitivity because counterfactual conditionals fail to contrapose.) Sosa claims that safety allows to avoid "abominable" conjunctions because although not-H is not sensitive, it is save and can thus be known if it is safety, rather than sensitivity, that is required for knowledge:
Here is the striking result: if we opt for safety as the right requirement then a Moorean stance is defensible, and we avoid skepticism. That is to say, one does satisfy the requirement that one's belief of not-H be safe: after all, not easily would one believe that not-H (that one was not so radically deceived) without it being true (which is not to say that not possibly could one believe that not-H without it being true). In the actual world, and for quite a distance away from the actual world, up to quite remote possible worlds, our belief that we are not radically deceived matches the fact as to whether we are or are not radically deceived.
However, it seems that sceptical arguments are based precisely on the fact that we cannot know whether we are deceived in the actual world. Is Sosa's argumentation, therefore, circular?