Philosophical Skepticism

Although this essay will consider some aspects of the history of philosophical skepticism, the general forms of skepticism to be discussed are.
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One of the best known of the early Greek Skeptics was Carneades c. During the 1st Century B. Towards the end of the 1st Century A. Later followers of Pyrrho and Carneades developed more theoretical perspectives, and Sextus Empiricus c. Sextus and his followers considered both the claims to know and not to know to be equally dogmatic , and claimed neither. Instead, despite the apparent conflict with the goal of ataraxia , they claimed to continue searching for something that might be knowable. Sextus Empiricus listed at least ten modes of skepticism , which can be broken down into three main categories: Much of the history of early Christian philosophy is an attempt to superimpose the new religion over Greek and Roman philosophical methods which were based on Skepticism and probable knowledge.

So early Christian thinkers such as St. Augustine and Boethius adapted the epistemological traditions of Greece and Rome to demonstrate that one could in fact arrive at certain knowledge at least in matters of Christian religion. After centuries of religious dogmatism throughout the Middle Ages, Skepticism again resurfaced during the late Renaissance , and particularly during the Age of Reason and the Enlightenment of the 17th and 18th Century. Montaigne in particular was willing to question the conventional wisdom of the time, calling into question the whole edifice of the educational system , and the implicit assumption that university-educated philosophers were necessarily wiser than uneducated farm workers.

Descartes established a methodological skepticism also known as Cartesian Skepticism in which he rejected any idea that can be doubted , and then attempted to re-establish it in order to acquire a firm foundation for genuine knowledge. His famous formulation "Cogito, ergo sum" is sometimes stated as "Dubito, ergo cogito, ergo sum" "I doubt, therefore I think, therefore I am". Descartes also posited the "dream argument" one of the most popular skeptical hypotheses , that the fact that it is so difficult to tell whether one is dreaming or not provides preliminary evidence that the senses that we use to distinguish reality from illusion should not be fully trusted.

In addition, he hypothesized the possible existence of an evil daemon or demon , which presents a complete illusion of an external world including other people to the senses, where in fact no such external world exists. This idea morphed much later into the brain in a vat thought experiment, in which a brain's perceived experiences , while held in a mad scientist's vat wired up to a super-computer, cannot be distinguished from the real thing.

David Hume , one of the British Empiricists , claimed that "A wise man, therefore, proportions his belief to the evidence", which provided the basis for the maxim of Marcello Truzzi - that " Extraordinary claims require extraordinary proof ", much later in the 20th Century. The eye emits radiation. The meeting of these two flows creates a kind of body, a physical object that constitutes the phenomenon.

The main consequence is that the object is never seen as itself. What we see is a kind of screen, which contains a mask, however, something of the subject eg, bloodshot eye sees a phenomenon red. The perception is relative. When Plato concludes that we must be wary of the vision and know the ideas, he concludes that Pyrrho can not know at all. Skeptics do not deny the existence of only the appearance of being, of truth. So I can say, not that honey is sweet, but it seems like. We must therefore remain undecided. These are the tropes.

For example, the sense organs are not the same depending on the animal species will therefore have different sensations. It can be concluded that the feeling is on the topic first trope. Depending on the circumstances one man does not necessarily see the same object in the same way. Thus, according to a man is young or old, healthy or sick, in motion or at rest and so on.

But it also varies by location, the position of the object, its distance second, third and fourth tropes. Far from it, we are presupposing that we do know some things about the world. In contrast, philosophical skepticism attempts to render doubtful every member of some class of propositions that we think falls within our ken. One member of the class is not pitted against another. The grounds for either withholding assent to the claim that we can have such knowledge or denying that we can have such knowledge are such that there is no possible way either to answer them or to neutralize them by appealing to another member of the class because the same doubt applies to each and every member of the class.

Thus, philosophical doubt or philosophical skepticism, as opposed to ordinary incredulity, can not, in principle, be removed. Or so the philosophical skeptic will claim!

Philosophical skepticism

To clarify the distinction between ordinary incredulity and philosophical doubt, let us consider two movies: The Truman Show and The Matrix. But he begins to wonder whether the world surrounding him is, in fact, what it appears to be. Some events seem to happen too regularly and many other things are just not quite as they should be. Eventually, Truman obtains convincing evidence that all his world is a stage and all the men and women are merely players.

The crucial point is that even had he not developed any doubts, there is, in principle, a way to resolve them had they arisen. Such doubts, though quite general, are examples of ordinary incredulity. Contrast this with the deception depicted in The Matrix. See Irwin , for collections of articles on The Matrix. The Truman Show is a depiction of a case of ordinary incredulity because there is some evidence that is, in principle, available to Truman for determining what's really the case; whereas The Matrix depicts a situation similar to that imagined by a typical philosophical skeptic in which it is not possible for the Matrix-bound characters to obtain evidence for determining that things are not as they seem whenever the virtual reality is perfectly created.

Put another way, the philosophical skeptic challenges our ordinary assumption that there is evidence available that can help us to discriminate between the real world and some counterfeit world that appears in all ways to be identical to the real world. Ordinary incredulity arises within the context of other propositions of a similar sort taken to be known, and, in principle, the doubt can be removed by discovering the truth of some further proposition of the relevant type.

On the other hand, philosophical skepticism about a proposition of a certain type derives from considerations that are such that they cannot be removed by appealing to additional propositions of that type—or so the skeptic claims. These movies illustrate one other fundamental feature of the philosophical arguments for skepticism, namely, that the debate between the skeptics and their opponents takes place within the evidentialist account of knowledge which holds that knowledge is at least true, sufficiently justified belief. The debate is over whether the grounds are such that they can make a belief sufficiently justified so that a responsible epistemic agent is entitled to assent to the proposition.

A corollary of this is that strictly reliabilist or externalist responses to philosophical skepticism constitute a change of subject. A belief could be reliably produced, i. Consider some proposition, p. There are just three possible propositional attitudes one can have with regard to p 's truth when considering whether p is true.

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For example, consider the belief that there is a god. The three possible propositional attitudes are: Of course, there are other attitudes one could have toward p when not considering whether p is true. One could just be uninterested that p or be excited or depressed that p. But, typically, those attitudes are either ones we have when we are not considering whether p is true or they are attitudes that result from our believing, denying or withholding p.

For example, I might be happy or sorry that p is true when I come to believe that it is true. Philosophers have differed about what that attitude is.

Philosophical skepticism and what skeptics really do

Some take it to be something akin to being certain that p or guaranteeing that p Malcolm , 58— Others have taken it not to be a form of belief at all because, for example, they claim that one can know that p without believing p as in a case in which I might in fact remember that Queen Victoria died in but not believe that I remember it and hence might be said not to believe it Radford For the purposes of this essay we need not attempt to pin down precisely the nature of the pro-attitude toward p that is necessary for knowing that p.

It is sufficient for our purposes to stipulate that assent is the pro-attitude toward p required to know that p. I will take such types of propositions to contain tokens some of which are generally thought to be known given what we ordinarily take knowledge to be. Thus, it would not be epistemically interesting if we did not know exactly what the rainfall will be on March 3 in New Brunswick, NJ, exactly ten years from now.

That kind of thing a fine grained distant future state is not generally thought to be known given what we ordinarily take knowledge to be. Now, consider this meta proposition concerning the scope of our knowledge, namely: We can have knowledge of EI-type propositions. Given that there are just three stances we can have toward any proposition when considering whether it is true, we can:. The attitude portrayed in 2 has gone under many names. I will follow the terminology suggested by Sextus Empiricus.

According to Sextus, they assented to the claim that we cannot have knowledge of what I have called EI-type propositions—although it is far from clear that this was an accurate description of their views. See the entry on ancient skepticism. Perhaps the prime example was Carneades — BCE. What underlies this form of skepticism is assent to the proposition that we cannot know EI-type propositions because our evidence is inadequate. The primary source of Pyrrhonian Skepticism is the writing of Sextus Empiricus who lived at the end of the second century CE. The Pyrrhonians withheld assent to every non-evident proposition.

That is, they withheld assent to all propositions about which genuine dispute was possible, and they took that class of propositions to include both the meta proposition that we can have knowledge of EI-type propositions and the meta proposition that we cannot have knowledge. Indeed, they sometimes classified the Epistemists and the Academic Skeptics together as dogmatists because the Epistemists assented to the proposition that we can have knowledge, while the Academic Skeptics assented to the denial of that claim.

Another difference between Academic and Pyrrhonian Skepticism is closely related to the charge by the latter that the former is really a disguised type of dogmatism. The Academic Skeptic thinks that her view can be shown to be the correct one by an argument or by arguments. The Pyrrhonian would point out that the Academic Skeptic maintains confidence in the ability of reason to settle matters—at least with regard to the extent of our knowledge of propositions in the EI-class.

A possible Cartesian reply could be as simple as paraphrasing Luther: Here I stand, as a philosopher with confidence in reason, and as such I can do no other. But regardless of the adequacy of either of the responses, the point here is that the Pyrrhonians did not claim that they had a compelling argument whose conclusion was that withholding assent to non-evident propositions was the appropriate epistemic attitude to have.

Although recently there has been a renewed interest in Pyrrhonism, it is fair to say that when contemporary philosophers write or speak about skepticism they usually are referring to some form of Academic Skepticism.


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Thus, we will now turn to that form of skepticism, and it is that form that will be the primary focus of this essay, although we will consider some aspects of Pyrrhonism later. However, in the voice of the non-skeptical interlocutor, he replies that even though the senses have misled him, he can neutralize that purported basis for doubt by pointing out that we are able to determine when our senses are not trustworthy. Thus, this is a case of ordinary incredulity because he appeals to some knowledge of the world gained through our senses to neutralize this basis for doubt. For example, in looking at a straight stick in water, even though it appears bent, we know from past sense experiences not to accept the testimony of our senses at face value in such situations because we have learned that straight sticks look bent in water.

Thus, we can neutralize the potentially knowledge-robbing proposition that my senses have deceived me on some occasions by conjoining it with another proposition to which we assent, namely, that I can distinguish between the occasions when my senses are trustworthy and those when they are not.

Thus, no basis for philosophical Academic Skepticism has been located. Descartes next seriously considers dreaming. Would he still have some knowledge of the external world? Yes; because in dreams and in waking life there are some common general features. So, if he were dreaming, he would not know in particular what is going on about him at that moment, but that does not imply that he fails to have any knowledge of the external world at that moment.

We have not found any reason for doubting that there are material objects in general or that they have a spatial location, or are in motion or at rest, or can exist for a long or short period of time. Again, no basis for Academic Skepticism has been established. For we can neutralize this apparent ground for doubting all of our beliefs about material objects because there are some truths about material objects and their properties that remain unchallenged in both our experiences while dreaming and our experiences while being awake. Thus, he sums up his reply to a skeptic's claim that for all we know, we might be dreaming now, as follows:.

Thus, Descartes believes that he has located a basis for doubting each of his supposed former pieces of knowledge about the external world that cannot be repulsed by locating another proposition to which he is entitled. He has found a proposition that, if true, would by itself defeat the justification he has for his assenting to propositions about the external world and at this point in the Meditations which is such that 1 he does not have a way to deny it and such that 2 he has no way to neutralize its effect.

That proposition can be put this way: My epistemic equipment is not reliable. It could be argued that the rest of the Meditations is designed to provide a way of showing that the Author of his being is perfect and, although he Descartes has made errors in the past, if his epistemic equipment is deployed properly and his will is constrained, error can be avoided. The characterization of genuine grounds for doubt could be put as follows:. Note that, given this characterization of genuine grounds for doubt, S need not have any evidential support for d. It could be any proposition that S entertains.

In addition, it could be false. Finally, it could be a ground for doubt for one person but not for another person or the same person at another time , depending upon what each believes at the time. For only one of them might have a belief that is adequate evidence for denying d or neutralizing d at the time.

That assumes, of course, that meditation can produce new adequately justified beliefs; but that seems reasonable enough for a philosopher to believe! The final step in arriving at the basis for Academic Skepticism is to claim that some proposition, say p , is not worthy of assent, or the pro-attitude required for knowledge, whenever there there is a genuine ground for doubting p.

Indeed, Descartes grants that even after d is located, p might still be more reasonable to believe than to deny Meditations , His point, though, is that the pro-attitude should not rise to the level required for knowledge because there is a genuine ground for doubt. Further, given the interpretation of the Meditations that we are now considering, the Cartesian-style argument for Academic Skepticism employs a very stringent requirement on the type of evidence required for knowledge.

In order for our beliefs to rise to the level of knowledge, they must be such that there remain no un-eliminated or non-neutralized defeaters, d , regardless of whether there is any evidence for believing that d. In more contemporary terminology, the ground for doubt proposed by Descartes can be put like this:.

There is a plausible way to weaken the requirement for genuine doubt by adding a fourth condition to conditions 1 — 3 above , namely, that d must have some evidential support; for example, it must have sufficient support to make it plausible enough so as to require that it be shown to be false or at least neutralized. The reason that is available to him is that he makes mistakes. A perfect potter would not make a pot with cracks. Interestingly enough, if I believe that I make mistakes, my belief must be true!

For, if I have made mistakes, the belief is true; and if I haven't made mistakes, the belief is true because I am making one now. The minimal counter-evidence requirement seems quite plausible. Why should any far-fetched hypothesis be worthy of serious consideration? We will return to the minimal counter-evidence requirement later.

But at this point, let us continue to take a genuine ground for doubt to be a proposition that only needs to satisfy conditions 1 — 3. With that in mind, the Cartesian-style template for the argument for Academic Skepticism can now be put like this:. This avoids that objection because the academic skeptic is neither assenting to the proposition that her equipment is untrustworthy nor assenting to the claim that there is an argument which shows that her equipment is untrustworthy.

She is merely assenting to the claim that U is a genuine ground for doubt for p. Thus, neither is she holding contradictory beliefs nor is her practice somehow inconsistent with what she assents to. The Cartesian-style argument for Academic Skepticism should be contrasted with what many contemporary philosophers take to be the canonical argument for Academic Skepticism which employs the Closure Principle CP.

This contemporary argument appeals to a form of the Closure Principle in Premise 1. A crucial feature of CP is that it does not depend upon employing a stringent notion of justification. Suppose that positive justification comes in degrees, where the lowest degree is something like mere plausibility and the highest degree is absolute certainty. That is a primary difference between the CP-style and what we have called the Cartesian-style argument for Academic Skepticism.


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Another difference is that the Cartesian-style argument concerns knowledge, whereas the CP-style argument concerns justification to whatever degree. Nevertheless, that difference is unimportant in this context because the debate about the merits of skepticism takes place within the evidentialist account of knowledge. EADP requires that we eliminate any genuine grounds for doubt and those include more than mere contraries propositions which are such that they both cannot be true, but they both could be false.

The proposition, c , would be a potential genuine ground for doubting h since if c were added to S 's beliefs, h would no longer be adequately justified because S 's beliefs would then contain a proposition, c , that entailed the denial of h.


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Furthermore, the only way S could eliminate c as a ground for doubt would be by denying it, since nothing could neutralize it. Thus, EADP has the consequence that if S is justified in assenting to h , then S is justified in denying every contrary of h. For example, the proposition, U , considered above is a grounds for doubting h , but h and U could both be true. Thus, there are two basic forms of Academic Skepticism: Since the CP-style skeptic employs the weaker epistemic principle, it will be best to begin by focusing on it because any criticisms of it will apply to the stronger form.

There appear to be only three ways that one can respond to the CP-style skeptical argument: The second alternative—denying the validity of the argument—has not been taken seriously by the anti-skeptic. If one were to deny that modus tollens is a valid form of inference, one would also have to deny the validity of i disjunctive syllogism and ii modus ponens or contraposition, since it is easy to transform modus tollens arguments into ones employing the other forms of inference.

Hence, if this alternative were chosen, reasoning would apparently come to a complete standstill. That, presumably, is why no one has ever seriously considered this alternative. So, if we are not to reluctantly embrace the conclusion, it appears as though we must reject either the first premise—an instantiation of closure—or the second premise. The basic issue is this: Does closure hold for justified belief? Closure certainly does hold for some properties, for example, truth. If p is true and it strictly implies q , then q is true. It just as clearly does not hold for other properties.

If p is a belief of mine, and p strictly implies q , it does not follow that q is a belief of mine. I might, for example, believe all of the axioms of Euclidean plane geometry, but fail to believe or perhaps even refuse to believe that the exterior angle of a triangle is equivalent to the sum of the two opposite interior angles. Every necessary truth is entailed by every proposition, and we can be justified in believing a false proposition. But surely S is not justified in believing every necessary truth whenever S has some justified belief in a false proposition.

In addition, some entailments might be beyond S 's capacity to grasp. Finally, there might even be some contingent propositions that are beyond S's capacity to grasp which are entailed by some propositions that S does, indeed, grasp. For example, I have ten 10 fingers entails the number of fingers I have is equivalent the square root of the sum of 9 squared plus the first prime number represented by numerals that sum to ten And it might be thought that S is not entitled to believe anything that S cannot grasp.

Philosophical skepticism and what skeptics really do

But it also appears that CP can easily be repaired. The skeptic can agree to those restrictions because the skeptical scenarios are posited in such a way as to render it obvious that our ordinary beliefs are false in those scenarios, and it is taken to be a contingent claim that S is in the actual circumstances as described in the antecedent. There is one other important, required clarification of the restricted version of CP.

It could be used to refer to a species of actually held beliefs—namely, those actually held beliefs of S that are justified. Or it could refer to propositions that S is entitled to hold—regardless of whether S does indeed hold them. Following Roderick Firth, the distinction between actually held justified beliefs and beliefs one is justified in holding, regardless of whether they are actually held, is often taken to be the distinction between beliefs that are doxastically justified and those that are propositionally justified.

In other words, one of S 's actual beliefs, p , might be justified and S still fail to believe some proposition, say q that is entailed by p. We are now in a position to ask: Does the restricted form of closure hold regarding what we are entitled to believe—even if we don't, in fact, believe it? There appears to be a perfectly general argument for the restricted version. Let p entail q , and let us suppose that S is entitled to believe that p iff S has non-overridden grounds that make p sufficiently likely to be true: The supposition mentioned above seems plausible given that the debate over the merits of Academic Skepticism employs an evidentialist account of justification.

That is, the debate between the Academic Skeptic and the Epistemist is over whether S has adequate grounds for EI-type propositions such that those grounds make p sufficiently likely to be true. Premise 2 contains the key claim. In spite of the fact that the probabilities whether subjective or objective transmit through entailment, it has been challenged. Fred Dretske and others have produced cases in which they believe CP fails and fails precisely because Premise 2 in the general argument for CP is false. The crucial thing to note about this proposed counterexample is that it works only if the Closure Principle entails that the very same source of evidence that justifies S in believing that the animals are zebras must justify S in believing that they are not cleverly disguised mules.

Thus, it could be held that this example could actually be used to support CP. Nevertheless, let us grant that S 's evidence for the claim that the animals are zebras cannot be used to show that they are not cleverly disguised mules. It could be argued that this would not force giving up Premise 2 in the general argument for CP. Such an argument could begin by recalling that Premise 2 claimed merely that whenever S had non-overridden grounds that make p sufficiently likely to be true, then S has non-overridden grounds for making q sufficiently likely to be true. It did not require that it was the very same grounds in both cases.

Dretske's purported counterexample seems to require that CP implies that the adequate source of evidence is the same for both propositions. No doubt this constraint sometimes correctly portrays the relevant evidential relationships when some proposition, p , entails some other proposition, q. For example, suppose I have adequate evidence for the claim that Anne has two brothers, then it would seem that the very same evidence would be adequate for believing that Anne has at least one brother. But the defender of CP, and more particularly the Academic Skeptic, could point out that closure does not require that all evidence paths to q are of the Pattern 1 type.

There are two other possibilities for instantiating closure that are captured by Premise 2 that can be depicted as follows:. In Pattern 2 cases there is some adequate evidence, e , for p ; and p , itself, is the adequate evidence for q , since p strictly implies q. For example, if I have adequate evidence for believing that 2 is a prime number, I can use that proposition as an adequate reason for believing that there is at least one even prime.

Indeed, consider any belief arrived at as a result of deductive inference. In such a case, we legitimately infer the entailed proposition from the conjunction of the premises that entails it.

Senses and applications

The plausibility of the famous Gettier cases depends upon Pattern 2 type cases in which closure holds. In Pattern 3 cases the order of the evidence is reversed because q serves as part of the evidence for p. For example, suppose that I am justified, ceteris paribus , in believing that pure water is present if I am justified in believing that there is present, at standard temperature and pressure, a clear, odorless, watery-tasting and watery-looking fluid that contains hydrogen and oxygen. Put another way, this instantiation of Pattern 3 cases would be consistent with interpreting Descartes as requiring that genuine grounds for doubt be propositions for which one has some evidence, however minimal, because a contrary to p for which one has some evidence that was not defeated would be a genuine grounds for doubt.

There is no way to neutralize the evidential effect of a contrary as there is with mere counter-evidence. Consequently, in order for S to be justified in believing that p, and assuming the Cartesian strong requirements for knowledge applied to justification, it appears that S would first have to be justified in denying any contrary of p for which she had minimal evidence before she could be justified in believing p.

The crucial point for the discussion here is that granting that there is no Pattern 1 type evidence path available to S in the zebra-in-the-zoo case does not require relinquishing premise 2 in the general argument for CP. The reason is simply that CP does not entail that there is Pattern 1 type evidence available in every case in which p entails q. That is, S can employ an evidence path like that depicted in Pattern 2.

See Klein , , and Further, if S had some reason to think that the animals were cleverly disguised mules, then S might have to eliminate that possibility before she could justifiably believe that they are zebras. In other words, S might have to employ an evidence path like the one depicted in Pattern 3.

The point is that the Dretske-like counterexamples appear to depend upon the false claim that if Premise 2 in the general argument for CP is true, then the evidential relationship between the entailing and the entailed proposition is always correctly depicted by Pattern 1. In addition to purported counterexamples to closure, there are some general theories of knowledge in which closure fails.

Robert Nozick's account of knowledge is the best such example. Roughly his account is this Nozick , — Think of a guided missile tracking its target. If the target were to move left, the missile would move left. If the target were not to move left, the missile would not move left. According to the tracking account of knowledge our beliefs must track the truth if we are to have knowledge.

There is one important clarification of conditions 3 and 4 discussed by Nozick, namely, that the method by which S acquires the belief must be held constant from the actual world to the possible world. A doting grandmother might know that her grandchild is not a thief on the basis of sufficiently good evidence, but would still believe that he wasn't a thief, even if he were, because she loves him.

So, we must require that the grandmother use the same method in both the actual and the near possible worlds, for, otherwise, condition 4 would exclude some clear cases of knowledge. This is not the place to provide a full examination of Nozick's account of knowledge. Suppose S knows that there is a chair before her. Would she know that she is not in a skeptical scenario in which it merely appears that there is a chair?

If the fourth condition were a necessary condition of knowledge, she would not know that because if she were in such a scenario, she would be fooled into thinking that she wasn't.