 Characterizing safety in these counterfactual terms depends on substantive assumptions about the semantics of counterfactual  conditionals.[19]  If we were to accept, for instance, David Lewis’s or Robert Stalnaker’s treatment of counterfactuals, including a strong centering condition according to which the actual world is always uniquely closest, all true beliefs would count as safe according to the counterfactual analysis of  safety.[20]  Sosa intends the relevant counterfactuals to be making a stronger claim, requiring roughly that in all nearby worlds in which S believes that p, p is not false.