Roots of Skepticism
The roots of skepticism run deep; they are not merely the invention of insecure philosophers. Perhaps the most primitive form of skepticism begins from a simple thought: belief is not the same as fact. Beliefs are in the mind; facts are in the world. Thus beliefs and facts can vary independently of each other: unknown facts, non-factual beliefs. Beliefs don’t necessarily hook onto facts, since they can be false; and facts sometimes decline to reveal themselves. So there is a gap between belief and fact, and in this gap the skeptic sees the possibility of error and hence lack of knowledge. It would be different if belief and fact were identical: then there would be no gap and fact would follow from belief. Knowledge would be guaranteed. But as it is, there is no such convergence of belief and fact, so skepticism is possible. Call this “non-convergence”: we can then say that one root of skepticism is non-convergence; and it is clearly a basic property of belief in relation to fact. Skeptical scenarios such as the brain in a vat or the evil demon are predicated upon it; it is what allows for these possibilities (as an identity theory of belief and fact would not). It is as if knowledge craves identity with fact, but cannot achieve this identity, so skepticism gains purchase. The skeptic gazes out at the world and reflects that his state of mind is not identical to the fact he takes himself to know, so the assumption of knowing that fact is not well founded. Notions like acquaintancehave been invoked to bridge the gap, but acquaintance is a relation between subject and object and hence presupposes non-identity; it cannot secure what knowledge apparently requires. So at least the skeptic suggests. Only identity would secure knowledge (the real McCoy), but that is an absurd theory of belief: belief and fact are distinct existences.
But there is another property of belief that is equally potent in triggering skeptical thoughts. This property is best appreciated in the wider context of the mind’s representational powers—what we might call the creativity of the mind. The mind is not a passive reflector of what comes in through the senses, faithfully mirroring what reality offers up. It creates mental representations: perceptions, dreams, illusions, hallucinations, imaginary objects, counterfactuals, nonsensical sentences, and erroneous beliefs. We might even say that it creates worlds, as with the brain in a vat or (more familiarly) dreams. It has the active power to generate representations that don’t correspond to facts—visual illusions being the most striking case. All of this has been fodder for skepticism: how can we rule out the possibility that the mind is always doing this? What is not often noted is that these skeptical thoughts trade on the fact that the mind has a certain sort of power or capacity: it is able to generate representations that fail to align with facts. Consider a mind that lacks such a power: it only stirs itself when facts heave into view. There are no dreams, no illusions, no imagination, and no false belief. Such a mind would not naturally lend itself to skeptical doubts: it would never say, “What if it’s all a dream?” or, “Maybe these perceptions are actually illusions”—for there are no such possibilities for this type of mind. This mind is not susceptible to skeptical worries simply because it never confuses fiction with fact or suffers a perceptual illusion or dreams a dream: it simply records what is actually present. It lacks the creative power necessary to produce the kinds of skeptical possibilities the skeptic is so impressed by. The human mind, by contrast, has this power in abundance; and it is this power that makes skepticism possible and natural for us. It is because the human mind is so creatively powerful that skepticism is so pressing for us. Skepticism arises from the strength of the mind not from its weakness. So we can add this property to the property of non-convergence as a source of skeptical sentiment. And clearly it too is a fundamental feature of the mind, as we know it to be. Skepticism thus has deep roots in the defining properties of the human mind (though not perhaps in all minds): we are natural skeptics because we know that our minds are such as to make skepticism possible.
I just described a possible mind in which skepticism can find no cause in creativity, which included the idea that such a mind has no false beliefs (possibly as a matter of natural law). But on reflection this thought experiment is not so obviously possible. What if I had claimed to describe a possible language in which no false sentences can be formed? Doesn’t the creativity of language guarantee that false sentences can be formed (they are well-formed and follow from the rules of grammar)? Similarly, if a person is capable of beliefs, isn’t she capable of having false beliefs? She just has to combine concepts in such a way that a false proposition results. The possibility of error is built into the ability to believe: to have beliefs about the empirical world is to have a mental attribute that makes error possible. That is precisely why we have so many false beliefs. But if error is possible, then knowledge is not possible, according to the skeptic. So what makes belief possible is what makes knowledge impossible! Belief is only possible if error is possible (by virtue of creativity), but if error is possible then knowledge is not possible (by the skeptical argument): so belief can never amount to knowledge by its very nature. A pre-condition for the existence of belief is the possibility of error, but the possibility of error rules out knowledge, so belief by necessity rules out knowledge. That gives skepticism very deep roots indeed; it follows from the essential nature of belief, as a manifestation of human creativity. The creative mind is necessarily haunted by the specter of skepticism, and belief is necessarily creative.
Now add to this the point that belief is a claim to know: when you believe a proposition you take yourself to know it. So thinking that you know is possible only if you can’t know! You can only think you know that p if you don’t know that p. The condition of thinking you know rules out the possibility of knowing: for thinking you know is an exercise of creativity, which implies the possibility of error, which implies the impossibility of knowledge. It is in the very nature of thinking you know that you don’t know (granted that the skeptic is right about knowledge requiring the impossibility of error). Thus belief can never amount to knowledge as a matter of its very constitution: it must contain the possibility of error, but then the skeptic seizes on that to question all claims to knowledge. I now know a priori that I cannot know, because I know that my beliefs arise from a creative faculty that permits the possibility of error, which rules out knowledge. I know that false beliefs are empirically common, and that I probably harbor many such beliefs; but I also know that there is no remedy for this situation–my belief system is so constructed that false beliefs can be generated by it. The system is a combinatorial generative faculty, like the language faculty, so the possibility of misrepresentation is built into it from the start. If (per impossibile) a belief system could restrict its outputs to those that correspond to facts, then this system would not be susceptible to the usual skeptical arguments; but that is a fantasy belief system, given that beliefs are combinatorial productions. It is like supposing that a dream system could be restricted to dreaming only what exists in reality.
Let’s assume the skeptical argument is correct: the possibility of error rules out knowledge. Then we can derive what deserves to be called a paradox of knowledge, namely that the conditions for the existence of knowledge make knowledge impossible. The conditions include the formation of beliefs (claims to know), but those conditions essentially involve the possibility of error, which is incompatible with knowledge. Knowledge is thus possible only if it is not possible! The skeptic has shown (granted his argument) not just that knowledge is impossible but also that it is in a certain way contradictory, for it requires an absence of error that is incompatible with its nature as a representational system. To know that p is for there to be no possibility of error regarding p, but that would imply that a necessary condition for being a belief system is not satisfied, which rules out the possibility of knowledge. Once a belief system exists the possibility of error exists, but that precludes those beliefs (claims to knowledge) from counting as knowledge. Skepticism is built into the very nature of belief as an instance of representational creativity. Creativity precludes knowledge (granting the connection between knowing and the impossibility of error). We could even say that concepts make knowledge impossible, because concepts are the things that make false propositions possible (just as words make false sentences possible). Concepts lead to the possibility of false beliefs, but that possibility rules out knowledge (as we are supposing). Suppose, for example, that I believe the table in front of me to be brown: I can reflect that this belief might be false, since my belief system might have constructed the wrong combination of concepts; but then I can’t be said to have knowledge that the table is brown. The point is that concepts in their nature can combine to create false beliefs, so skepticism has roots in the nature of concepts. Knowledge is therefore not possible for creatures that think in concepts—but what other way is there to think? We feel the pull of skepticism because we see that it has its roots in the nature of thought itself. The paradox of knowledge is that what allows us to seek knowledge prevents us possessing it—the structure of our cognitive faculty. The only way to vanquish skepticism is to do away with our cognitive faculty—but then we are left with nothing to know with.
The situation can be compared with perception. Our visual system purports to give us direct access to material objects, but according to the sense datum theorist it does not, but rather gives us direct access only to our own sense data. So we don’t really perceive what we naively think we perceive. But the point is not just that we happen not to perceive material objects directly, but rather that it’s built into the nature of perception that we don’t: for perception yields experiences and these are what is directly perceived (allegedly). The roots of the sense datum theory are thus claimed to lie in the very nature of sensory experience and are not dispensable—no one could see the world directly. Yet our experience leads us to believe that naïve realism is true. So there is something paradoxical about sensory experience: on the one hand, it presents itself as the direct perception of external objects; but on the other, its very structure contradicts that impression. It purports to do what its own nature precludes it from doing. So for the sense datum theorist naïve realism is not just a false theory of perception but also necessarily false, and reveals perception as paradoxical. Experience represents itself as doing what its own nature makes impossible. It endorses naive realism while also being incompatible with it. Similarly, our belief system represents itself as containing knowledge, but in its very nature it makes knowledge impossible. Experience makes us think we see the world directly, but at the same time its nature rules that out (according to the sense datum theorist); belief makes us think we have knowledge, but at the same time its nature rules that out (according to the skeptic). So the problems alleged by these doctrines go deep into the nature of the mind: the mind is telling us we can have states (direct perception, knowledge) that we cannot in fact have, given the way the mind is constituted. The nature of mind excludes its own assertions about itself.
I am not saying that skepticism is true, or that the sense datum theory is true; I am merely pointing out that both doctrines, rightly understood, go deeper than is generally supposed. First, they are necessity claims; second, they detect paradox in our ordinary concepts of knowledge and perception. In the case of knowledge, our concept requires something that is manifestly impossible, namely belief that is incapable of combining concepts in ways that fail to match reality. For once we accept that the mind has the power to create false beliefs we are well on the way to skepticism. This (combined with non-convergence) is what fundamentally leads to skepticism: belief is just not cut out to constitute knowledge.
 I discuss skepticism in relation to knowledge in this paper, but it would also be possible to frame the discussion using the notion of certainty or justified belief or other epistemic notions. Questions about whether knowledge really requires ruling out the possibility of error will not detain me, since I am concerned with what leads to skepticism in general; focusing on knowledge simplifies the discussion.
 I say “about the empirical world” so as to make a possible exception for introspective beliefs. Here it may be said that the combinatory power of concepts does not lead to the possibility of error, since I can know infallibly that I am in pain and yet my introspective belief is composed of a structured proposition. That would not contradict the claim that beliefs about the material world must be capable of error, but it might seem to limit the scope of the error thesis. This is a difficult question that I will not pursue here, but let me observe that there is a real tension between the idea of introspective certainty and acceptance of the combinatorial nature of belief: for how could a belief be incapable of falsity if its content is composed of combinable concepts? Shouldn’t skepticism carry over to so-called introspective knowledge? Not for nothing did Wittgenstein doubt that such statements are really propositional.
 It should be clear that by “creative” I don’t mean the kind of creativity we find in the arts and sciences but simply the kind of creativity inherent in the language faculty—what is sometimes called “productivity”.
 We might reasonably conclude that (some) animal knowledge is more immune to skepticism than human knowledge, on the assumption that animal knowledge is not always conceptual or belief-based. Certainly animals are not as troubled by skepticism as we are (though capable of error).