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First Meditations on the Skeptical Philosophy

Identifying Controversial Presuppositions Within The Cartesian Skeptical Argument

Apr 02, 2009


One strength of the Cartesian skeptic's argument is its apparent lack of controversial presuppositions. But is this really the case? What might the skeptic need to presuppose for their argument to have any force? If the skeptical argument does contain presuppositions, is it correct to say that they are uncontroversial?

This paper will argue that the skeptical argument does in fact contain presuppositions, and that the skeptic's position is not entirely intuitive, and thus that these presuppositions are controversial.

In order to explain what it is that makes the skeptic's presuppositions controversial, this essay will begin with a clarification of the skeptic's argumentative structure, which will in turn enable identification of the skeptic's presuppositions. Having exposed the skeptic's presuppositions, this essay will close with an examination of their controversial nature.

The Skeptical Argument's Structure

Descartes' motivation in formulating the skeptical argument was to determine which of his beliefs could justifiably be regarded as knowledge. In order to reduce his chance of falling into error he began the project of knowledge identification with the complete and "general destruction of ... former opinions," which was accomplished by "rejecting them all." Starting from a position of unrestricted doubt, Descartes went on to examine his extant beliefs and set about the task of explaining their origins.

While writing Meditation One, Descartes was seated at his fireplace, and in reflecting on the belief that he was seated at his fireplace, he discovered that it was possible to construct multiple explanations for this experience, but impossible to select one explanation over another. The most obvious or common explanation for Descartes' experience was that his beliefs were an accurate representation of the external world; he appeared to be seated at his fireplace because he was in fact seated at his fireplace. But might he be dreaming? How often had "slumber persuaded [him] of such customary things as" this experience? In raising this possibility, Descartes found "no definite signs to distinguish being awake from being asleep," and so he reasoned that perhaps he was in fact dreaming, in which case his beliefs did not provide an accurate account of reality, because in reality he was asleep in bed. But if it was possible that he was dreaming and the external world was not the source of his experience, were there other potential sources of experience? Could an all-powerful evil genius have constructed a rich illusory environment that ensnared Descartes, and this was the source of experience? Descartes found yet another explanation for his experience, but still no method for selecting one explanation over another. Recognizing the inconclusive character of his predicament, Descartes concluded that all beliefs were subject to doubt. Consequently, if all beliefs were subject to doubt, then it would be impossible to justify beliefs about the external world.

Meditation on the circumstance that Descartes possessed three explanations (reality, dream, and evil genius) for one experience (Descartes awake and seated by his fireplace) reveals the first element of the skeptical argument: i) a single set of evidence was congruent with multiple conflicting explanations, and ii) there was no criteria for distinguishing any explanation as more appropriate than another. Translating into epistemological parlance: all explanations had the same observational consequences, and hence the explanations were underdetermined by the evidence. This principle, underdetermination, is the first component of the skeptical argument.

To find the second structural component of the skeptical argument, we must answer the question of knowledge: if beliefs about the external world cannot be justified as knowledge, then what beliefs may justifiably be regarded as knowledge? Descartes' basic claim, "that the statement 'I am, I exist' is necessarily true every time it is uttered by me or conceived in my mind," assumes that the capacity for thought can be regarded as implying existence. If thinking implies existence, then experience of existence must be possible, or else we would not experience thought. If experience of existence is possible, then even though it was impossible for Descartes to justify the claim that he was in reality sitting awake by his fireplace, it is not possible that he was wrong to claim that in his experience of existence it appeared to him as though he was sitting awake by his fireplace. Hence, we cannot be wrong about the content of experience -- sense-data. The essential principle at work here is the privacy of experience, and it is this principle that provides the second and final component of the skeptical argument.

Though Descartes concentrated only on problems regarding the external world, the phrase "Cartesian skepticism" now refers to a set of problems that employ this general skeptical structure; underdetermination combined with the privacy of experience. The most notable problems include knowledge of: other minds, the past, the future, and general claims about the world such as the laws of physics.

Does The Skeptical Argument Contain Presuppositions?

Descartes concluded that the only thing we cannot be wrong about was sense-data, but what is the connection between sense-data and knowledge? The skeptic argues that knowledge of the external world is assembled from sense experience via arguments. Explanations of the world are developed based on the way we experience the evidence of our sense-data, and these results are applied in the formation and application of knowledge. Here we arrive at the skeptic's first presupposition: in reasoning that knowledge of the external world is constructed from sense-data, the skeptic presupposes that knowledge of the world is inferential.

Apprehension of the first presupposition leads directly to recognition of the second. The skeptic argues that beliefs about the external world are unjustified inferences from sense-data, but this does not prove that inductive inference is a weak ampliative strategy, it presupposes that the weakness of inductive inference as an ampliative strategy is self-evident.

The skeptic's third presupposition is simply that their conclusion is problematic -- at all. This is the reductionist response to skepticism, which rejects the skeptic's conclusion entirely.

Having verified the existence of presuppositions in the skeptical argument, what can we say about the nature of these presuppositions?

Are The Skeptic's Presuppositions Uncontroversial?

The skeptic's first presupposition, that knowledge of the world is inferential, provides a very limited basis for knowledge because all other claims may only be inferred from sense-data. This presupposition finds opposition in the perceptual claims of direct realism. The direct realist claims that observations are inherently reliable, and that individual knowledge claims are "embedded in an extensive body of collateral knowledge about the world and our place in it." For the direct realist, the world is composed of external mind-independent objects, and these objects are the direct and immediate substance of our experience. Ergo, direct realism stands in direct opposition to the skeptic's first presupposition.

The skeptic's second presupposition, that inductive inference is a weak ampliative strategy, may be countered by the defense that the skeptic does not understand inductive justification, and indeed may not be able to understand inductive justification. It cannot be taken for granted that induction is a straightforward and comprehensible process. A typical inductive inference does not include observational data indiscriminately. Instead, information is included based on its theoretical relevance. The fact that a skeptic can construct an argument to explain experience by way of dreaming shows only that it is possible to generate different interpretations of experience, not that all interpretations should be regarded as having equal inferential potential. In the skeptic's second presupposition we are again met with controversy.

The skeptic's third presupposition, that we should acknowledge their argument as a significant source of difficulty, finds a counterargument in the reductionist stance. The skeptic argues that there is a gap between the external world and our experience of the external world. The reductionist asserts that there are logical and conceptual links between belief and experiential knowledge, and therefore the skeptic's gap does not exist. The skeptic claims it is possible to construct more than one explanation for an experience, but it is impossible to determine which explanation is objectively accurate. The reductionist replies that the skeptic is presupposing there is meaning beyond sense-data, and claims that when we are describing experience we must reduce "external object talk" to "sense-data talk." At this point, the reductionist presents the skeptic with a list of permanent possibilities of experience; the collection of all possible sense-data experiences related to the phenomena in question. Regardless of the explanation that the skeptic provides for an experience, the reductionist argues that because the sense-data experiences are all the same, there is no room for skeptical doubt. Once again, we find controversy.

Though it is possible to continue further development of these responses to the skeptic's presuppositions, the truth of the claim that the skeptical argument contains controversial presuppositions has now been established.


In reflecting on his experiences, Descartes observed that the process of knowledge accretion was not as simple as the passive acquisition of data. The dubious character of knowledge claims motivated Descartes to examine the foundations of knowledge and to formulate his skeptical argument. The goal of this argument was to discard all claims that might be doubted, and thus restrict knowledge to claims that could be justified.

Though there is no universally accepted resolution for Descartes' skeptical argument, it is notable that in constructing his argument Descartes was unable to avoid working from presuppositions that were themselves not intuitive and unquestionably justified.

Part of the series: UWO