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Skepticism and Dretske's Zebra
by Dr. Laxminarayan Lenka, NEHU, Shillong-22, Meghalaya, India

(This paper is an earlier draft of my "On the Zebra that shatters certain arguments for skepticism", to be read at a national seminar on Epistemology & Cognition in Comparative Perspective, Department of Philosophy, University of Hyderabad, Hyderabad, India, from 19th to 21st March, 2007.)

I welcome your comments.My email ID is lenkanehu@yahoo.co.in

Abstract: We do not know anything because we do not know the very thing that follows from anything we know. This important form of argument for skepticism presupposes the Principle of Knowledge Closure: Conjunction of a known implication and its known antecedent guarantees that the consequent is known. Dretske's Zebra case challenges the validity of Knowledge Closure and, thereby, the validity of certain skeptical arguments. Klein(1981) and Stine(1976) have criticized the Zebra case on different grounds. In this paper, I have given an exposition of (a) The Dream Argument, (b) The Evil Genius Argument and (c) The Brain in a Vat Argument to explain how they serve as arguments for skepticism in the said important form and how each of them presuppose the principle of Knowledge Closure. Then, considering the criticisms of Klein and Stine, I propose a Tautology Case against the principle of Knowledge Closure and calim the case to be overcoming those criticisms without defeating the purpose of the Zebra case.

The Dream Argument:

What we see in dreams need not be true. Our waking states are not disinguishable from our dreaming states. Therefore, what we see even in our waking states need not be true.

Nothing based on sense experience is an instance of knowledge (with certainty) since (i) Any verb coresponding to a sense experince can replace 'see' in the above argument without affecting its validity. (ii) If something need not be true then it is not ceratin and uncertainty implies doubt equivalent to not-knowledge.

In sofar as we are not certain of that we are not dreaming now, we are not certain of that what we experience now is there in reality and not in dreams. I see that I am in this room with others. The same might not be true but a dream, I might be sleeping on my bed and dreaming that I am in the class room. You may pinch me to make me feel that I am in the waking state and I may feel pain when you pinch me. But as the same can be a content of one of my dreams, what is the guarantee that I am not dreaming now? If everything I experience in a waking state can be experienced through dreams, no experience stands as the criterion to distinguish my waking sates from my dreaming states.

In accordance to the Dream Argument, you do not know that p, if you do not know that q; when p stands for any proposition expressing an instance of your sense-experience and q for the proposition "You are not dreaming". You do not know that you are seeing me, even if you are seeing me, if you do not know that you are not dreaming. Of course, that you are actually seeing me and that you are dreaming that you are seeing me cannot be true together. But, why cannot you know the former if you are unable to distinguish it from the latter? The answer presupposes that the Principle of Knowledge Closure (KC) is true. The following argument is the answer. If You know that p (= You are actually seeing me) & You know that p entails q (you are not dreaming that you seeing me) then You know that q. Since you do not know that q, either you do not know that p or you do not know that p entails q. You know that p entails q. Therefore, you do not know that p.

The Evil Genius Argument:

If you know that p then you know that you are not deceived by Descares' Evil Genius (Demon) You do not know that you are not deceived by Descartes' Evil Genius Therefore, you do not know that p.

Any criterion put forth for your knowing of not being deceived by the Evil Genius can be marked as an instance of being deceived by the Evil Genius.

It is logically possible that the demon deceives you. Now, even if you do not know that it does not deceive you, why should not you know that p (say, 2+2=4)? That is, even if the 2nd premise is acceptable, how is the 1st premise acceptable? How does your knowledge of not being deceived by the Evil Genius necessarily follow from your knowing that p? The skeptic presupposes that the principle of Knowledge Closure is true and, in accordance to this principle, the following is a valid argument. You know that 2+2=4 You know that if 2+2=4 then you are not deceived by the Evil Genius Therefore, you know that you are not deceived by the Evil Genius

This is how, in accordance to the skeptical argument, it becomes neccessary that you know that you are not deceived by the Evil Genius, if you know anything, say, you know that 2+2=4.

The Brain in a Vat Argument:If you know that you are reading a paper you know that you are not a Brain in a Vat. You do not know that you are not a Brain in a Vat. Therefore, you do not know that you are reading a paper.

If you are a Brain in a Vat, you are no better than a vegetable but your brain has been technologically managed to make you feel and think that you are absolutely normal. You have no perceptual evidence of looking at a piece of paper but that is one of the important things that matters for your knowing that you are reading a paper.You cannot take help from the public because each of them could very well be a Brain in a Vat.

Why should you know that you are not a Brain in a Vat if you know that you are reading a paper? The answer (given below) presupposes the validity of Knowledge Closure.

You know that you are reading a paper. You know that if you are reading a paper then you are not a Brain in a Vat Therefore, you know that you are not a Brain in a Vat.

So far we discussed on that the principle of KC is presupposed by different arguments for skepticism. Now we switch on to the Zebra that shatters these arguments for skepticism by refuting the KC.

Dretske's Zebra:Fred sees a zebra in a zoo. Fred's eye sight is alright, he is at a close distance from the animal he is looking at, the animal has been pen-marked as "Zebra". Fred has sufficient evidence that justifies him to hold the belief that the animal in front of him is a zebra. In fact, it is a zebra. Thus Fred knows that it is a zebra.That z (=It is a zebra) entails that m (= it is not a mule cleverly presented as a zebra) is a known entailment for Fred. However, Fred is not justified in believing that m, hence, Fred does not know that m. It becomes a couter-example to KC. Fred knows that z and knows that z entails m but does not know that m.

Why is it that Fred does not know that m? The set of evidences sufficient to justify Fred's belief that z is is not sufficient to justify Fred's belief that m. The m-evidences are not contained in the z-evidences. For example, fred has not checked or verified the honesty and sincerity of the zoo authority for the belief that z and yet justified in believing that z; but in not verifying so Fred is not justified in believing that m.

If the zebra case is alright, KC is refuted and, thereby, skeptical arguments presupposing KC are refuted.

Your belief that a (=You are actually seeing me) is justified even if your belief that d(=You are not dreaming now) is not justified and you know that a entails d and know that a. You are justified in believing that t (2+2=4) even if you are not justified in believing that e (=You are not deceived by the Evil Genius) and you know that t entails e and know that t. You are justified in believing that p(=You are reading a paper) even if you are not justified in believing that v(=You are not a BIV) and you know that p entails v and know that p.

Klein's Criticism:

Although the z-evidences do not contian the m-evidences, the z-evidences plus Fred's knowledge that z entails m does justify Fred's m-belief. In other words, refutation of KC does not follow from the fact that Fred has the justified z-belief and an unjustified m-belief, but only if it so happens when Fred's knowledge of the entailment is included under the evidences for Fred's m-belief. Inclusion of this known entailment as an evidence, acording to Klein, does make Fred justified in believing that m.

Stine's criticism:Fred's m-belief needs no evidence once Fred knows that z. Dretske is right in claiming that the m-belief is not a relevant alternative that blocks the knowledge of z. But, the exclusion of m-belief from the set of relevant alernatives does not prove that Fred does not know that m. On the contrary, it proves that the knowledge of m is not to be claimed, in normal circumstances and, hence, not in need of evidence.The z-belief presupposes the m-belief in a manner that makes it misleading to claim the knowledge of m when the knowledge of z is claimed. It would be like claiming that my wife is either in the kitchen or in the bed room after claiming that my wife is in the kitchen, although, literally, the former is true if the latter is true. In normal circumstances, it is odd to claim both.

The Tautology Case: I propose the folowing counter-example to KC and claim that it overcomes criticisms made by Klein and Stine on the Zebra Case.

In a question-answering session, you are asking and I am answering questions in the following way. Do you know that you do not know every tautology? Yes. Do you know that 2+2=4? Yes. Do you know that every tautology is implied by any proposition whatsoever? Yes. Do you know that even if you do not know a tautology t, any proposition does imply t? Yes. Do you know that even the proposition 2+2=4 implies that t? Yes.

Now, if I am right in answering "Yes" in each case, and I think I am right, then, I know that 2+2=4, know that t is implied by 2+2=4 and yet I do not know that t. Thus KC fails.

References:

1. De Rose K. &Warfield T.A. (Ed.), Skepticism: A Contemporary reader, Oxford Univ. Press, New York. 2. Dretske, F (1970), "Epistemic Operators", Journal of Philosophy, 67, pp. 1007-1023. 3. Haldane, E. & Ross G.R.T. (1967) Rene Descartes, Meditations on First Philosophy, Cambridge univ. Press, Cambridge. 4. Klein P.D. (1981), Certainty:A Refutation of skepticism, The Harvester Press Ltd., Great Britain. 5. Putnam H. (1981) "Brains in a Vat" in his Reason Truth and History, Cambridge University Press 6. Stine G. (1976) "Skepticism, Relevant Alternatives, and Deductive Closure", Philosophical Studies, 29, pp. 249-261.

--Laxminarayan Lenka, Department of Philosophy, North-Eastern Hill University, Shillong-22, India 10:58, 2 March 2007 (UTC)