 Much of modern epistemology aims to address one or another kind of skepticism. Skepticism is a challenge to our pre-philosophical conception of ourselves as cognitively successful beings. Such challenges come in many varieties. One way in which these varieties differ concerns the different kinds of cognitive success that they target: skepticism can challenge our claims to know, or our claims to believe justifiably, or our claims to have justification for believing, or our claims to have any good reasons for belief whatsoever. But another way in which these varieties differ is in whether the skepticism in question is fully general—targeting the possibility of enjoying any instance of the relevant cognitive success—or is selective—targeting the possibility of enjoying the relevant cognitive success concerning a particular subject matter (e.g., the past, the minds of others, the world beyond our own consciousness) or concerning beliefs formed by a particular method (e.g., perception, memory, reasoning, etc.). General skepticism and selective skepticism pose very different sorts of challenges, and use very different kinds of arguments. General skepticism is motivated by reasoning from some apparently conflicting features of the kind of cognitive success in question. For instance, a general skeptic might claim that justification requires a regress of justifiers, but then argue that this regress of justifiers cannot be contained in any finite mind—and thus, the skeptic might conclude, no finite being can be justified in believing anything. Alternatively a general skeptic might claim that knowledge requires certainty, and that nobody can be certain of something unless there is nothing of which she could be even more certain—thus, the skeptic might conclude, we can know virtually nothing (see Unger 1975).