Cartesian Skepticism

Cartesian skeptics invite us to explain how knowledge of (or justified belief about) the external world is possible given the challenge that we cannot know (or justifiably believe) the denials of skeptical hypotheses, such as that one is dreaming or a brain-in-a-vat. The problem has its source in Rene Descartes’ Meditations on First Philosophy, and in particular, the First Meditation. 

For example, Descartes considers the hypothesis that there is a powerful evil demon who renders his beliefs about the world false, while making it seem to him just as if they are true. The challenge Descartes raises is this: how can we know that the evil demon hypothesis is false? External world skepticism is view that that knowledge (or justified belief) about the external world is impossible. An external world skeptic is a Cartesian skeptic if they appeal to skeptical hypotheses in order to show that we cannot know (or justifiably believe) anything about the external world. The Cartesian skeptical argument is often presented as follows: (1) If you know that an external world proposition P is true, then you know that the skeptical hypothesis SH is false. But (2) you don’t know that SH is false. Therefore, (3) you do not know that P. 

Responses to the Cartesian skeptical argument can be divided into those which maintain that premise 1 is defective and those which maintain that premise 2 is defective. Mooreans rejects premise 2, arguing that we can know the denials of skeptical hypotheses by way of competent deduction from our ordinary external world knowledge. Different theorists have tried to support the Moorean view in different ways (e.g., dogmatist, reliabilist, knowledge-first, and disjunctivists). Relative Alternatives Theorists argue that skeptical hypotheses are not relevant alternatives to our ordinary knowledge. Many relevant alternative’s theorists reject the closure-principle and thereby premise 2. Contextualists argue that the truth-conditions of our knowledge-ascriptions are sensitive to context, allowing that, in ordinary contexts, ascriptions of ‘S knows that P’ can be true even though, in skeptical contexts, ascriptions of ‘S knows that P’ are false.

Some philosophers argue that there are pragmatic reasons to maintain our ordinary beliefs, even if they are in some way epistemically defective according to Cartesian skeptics. Veridicalists have argued that some skeptical hypotheses, like the BIV or simulation hypothesis, are compatible with the truth of our ordinary beliefs. 

For the original presentation of Cartesian skepticism and the Cartesian skeptical argument, see Descartes 1960. For work on the nature of the Cartesian skeptical argument, see Unger 1975, Nozick 1981, Stroud 1984, Williams 1991, and Pryor 2000. For work on closure-based and underdetermination-based formulations of the argument, see Yalçin 1992, Brueckner 1994, Cohen 1998, Vogel 2004, and Pritchard 2005. A classic response to Cartesian skepticism is Moore 1959. For Moorean responses from epistemic externalism, see Hill 1996, Sosa 1999, Greco 2000, and Pritchard 2005. For knowledge-first variants, see Williamson 2000. For dogmatist responses, see Pryor 2000, and Huemer 2000. For epistemological disjunctivist responses, see McDowell 2008 and Pritchard 2012. For explanationist responses, see Vogel 2013 and Vogel 1990. For entitlement responses, see Wright 2004. For a priori argument responses, see Kant 1929, Putnam 1981, and Davidson 1986. For truth-tracking responses, see Nozick 1981, and Zalabardo 2012. For relevant alternatives responses, see Dretske 1970 and Stine 1976. For contextualist responses, see Cohen 2000, Lewis 1996, and DeRose 1995. For pragmatic responses, see Rinard 2021. For a recent veridicalist response, see Chalmers 2018.