“A Variety of Arguments for Cartesian Skepticism and Their Presuppositions”

Abstract

This paper aims to elucidate various arguments for Cartesian skepticism, reveal their presuppositions, and examine their plausibility. Cartesian skepticism concerns knowledge of the external world in general. Even though there are different arguments for Cartesian skepticism, their differences are often neglected, resulting in serious confusions. By analysing the premises and presuppositions of each argument, I attempt to figure out whether and to what extent it is plausible.
The paper consists of seven sections. In Section 1, I introduce the problem of Cartesian skepticism. Then, from Sections 2 to 4, I review three different forms of the argument from ignorance, which appeal to different variants of the epistemic closure principle about knowledge. Among them, the standard closure principle is more plausible than the other two; one requires that S be logically omniscient, and one entails the notorious KK thesis that first-order knowledge requires second-order knowledge. The requirements these two closure principles impose on knowledge, then, are too strong. In Section 5, I discuss how versions of infallibilism are invoked in defending the first premise of the argument, viz., that S does not know that a skeptical hypothesis is false, of the argument from ignorance. On the other hand, some claim that the argument from underdetermination does not require infallibilism, and thereby undermines even fallible knowledge. In Section 6, however, I argue that it is hard to maintain that the argument from underdetermination fares well against fallible knowledge. The underdetermination principle, to which the argument appeals, is supported by premises at odds with fallibilism. In addition, the argument from underdetermination faces another problem: it presupposes that S's total evidence is restricted to sensory evidence, if it works against fallible knowledge at all. Since this presupposition is contentious, the argument from underdetermination against fallible knowledge needs more justification for its presuppositions, in order to get off the ground. Section 7 gives a summary of the paper.