External World Skepticism John Greco* Saint Louis University Abstract Recent literature in epistemology has focused on the following argument for skepticism (SA): I know that I have two hands only if I know that I am not a handless brain in a vat. But I don’t know I am not a handless brain in a vat. Therefore, I don’t know that I have two hands. Part I of this article reviews two responses to skepticism that emerged in the 1980s and 1990s: sensitivity theories and attributor contextualism. Part II considers the more recent ‘neo-Moorean’ response to skepticism and its development in ‘safety’ theories of knowledge. Part III argues that the skeptical argument set out in SA is not of central importance. Specifically, SA is parasitic on skeptical reasoning that is more powerful and more fundamental than that displayed by SA itself. Finally, Part IV reviews a Pyrrhonian argument for skepticism that is not well captured by SA, and considers a promising strategy for responding to it. Much of the recent literature in epistemology has focused on the following skeptical argument. 1 SA Let o be some ordinary proposition about the external world, such as that I have two hands, and let h be a proposition describing some skeptical hypothesis, such as that I am a handless brain in a vat. 1. I know that o only if I know that ¬h. 2. But I don’t know that ¬h. Therefore, 3. I don’t know that o. The argument generalizes: we can take nearly any proposition about the external world, and we can choose a suitable skeptical hypothesis so as to generate an argument with a similar form. A robust skepticism about the external world threatens. Part I of this article reviews the two major responses to SA that emerged in the 1980s and 1990s: sensitivity theories and attributor contextualism. Some objections that have been raised against these anti-skeptical responses are also reviewed. Part II considers a third anti-skeptical response to SA that has emerged more recently. This ‘neo-Moorean’ response can be taken in a number of directions, but here we focus on its development in ‘safety’ © 2007 The Author Journal Compilation © 2007 Blackwell Publishing Ltd Philosophy Compass 2/4 (2007): 625–649, 10.1111/j.1747-9991.2007.00090.x