The paper purports to show that in order to formulate the hypothesis that all our beliefs are collectively false - which is taken to be the core of Cartesian skepticism - one must accept the presumption that semantic properties of subject's beliefs locally supervene on 'internal' properties of said subject. In order to show that the responses to skepticism from semantic externalism, i.e. those formulated by Putnam and Davidson, are analyzed. It is argued that even though these arguments are controversial they indicate that Cartesian skeptic must assume that subject beliefs' semantic properties can remain the same in different surroundings, which is exactly what the supervenience thesis amounts to. Finally, it is pointed out that the skepticism introduced by Kripke in his discussion of rule-following is indeed more radical than traditional, Cartesian one, as the former denies the very thesis that the latter must assume.