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Philosophical skepticism (UK spelling, scepticism) is the philosophical school of thought that critically examines whether knowledge and perceptions are true and whether one can ever have true knowledge.
- See also: Scientific skepticism
History of skepticism
In the ancient west
The Western tradition of systematic skepticism goes back at least as far as Pyrrho of Elis. He was troubled by the disputes that could be found within all philosophical schools of his day, including his own philosophy of Stoicism. According to a later account of his life, he became overwhelmed by his inability to determine rationally which school was correct. Upon admitting this to himself, he finally achieved the inner peace that he had been seeking.
From a Stoic point of view, Pyrrho found peace by admitting to ignorance and seeming to abandon the criterion by which knowledge is gained, logical reason. Pyrrho's ignorance was not the ignorance of children or farm animals: it was a knowledgeable ignorance, arrived at through the application and exposition of the inadequacy of logical reasoning. The school of thought developed primarily in opposition to what was seen as the dogmatism, or ultimately unfounded assertion, of the Stoics. Pyrrhonists made distinctions between "being" and "appearing" and between the identity and the sensing of a phenomenon.
Pyrrho and his school were not actually "skeptics" in the later sense of the word. They had the goal of αταραξια (ataraxia - peace of mind), and pitted one dogmatic philosophy against the next to undermine belief in the whole philosophic enterprise. The idea was to produce in the student a state of aversion towards what the Pyrrhonists considered arbitrary and inconsequential babble. Since no one can observe or otherwise experience causation, external world (its "externality"), ultimate purpose of the universe or life, justice, divinity, soul, etc., they declared no need to believe in such things. The Pyrrhonists pointed out that, despite claims that such notions were necessary, people "ignorant" of them get by just fine before learning about them. They further noted that science does not require belief and that faith in intelligible realities is different from pragmatic convention for the sake of experiment. For each intuitive notion (e.g. the existence of an external world), the Pyrrhonists cited a contrary opinion to negate it. They added that consensus indicates neither truth nor even probability. For example, if the earth is round, it remains so even if everyone believed it were flat.
The goal of this critique, which Pyrrho's followers realized would ultimately subvert even their own method, was to cultivate a distrust of all grand talk. They expected philosophy to collapse into itself. How far in this direction the Pyrrhonean commitment extended is a matter of debate. The Pyrrhonists confessed a belief in appearances, e.g. in hot and cold, grief and joy. It is impossible to deny, they admitted, that one seems to be in pain or seems to touch a piece of wood. Their world, thus, was completely phenomenological. An accomplished Pyrrhonist could, ideally, live as well as a dogmatist but with the added benefit of not worrying about truth and falsity, right and wrong, God's will, and so forth.
Later thinkers took up Pyrrho's approach and extended it into modern skepticism. In the process, a split appeared within the movement, never too large or well-liked among the literati to begin with. In the New Academy, Arcesilaus (c. 315-241 B.C.) and Carneades (c. 213-129 B.C.) built theoretical perspectives around firm denial of the possibility of certain, immediate knowledge, instead suggesting an early probabilistic account of it. Sextus Empiricus (c. A.D. 200), the main authority for Greek skepticism and a follower of Pyrrho, worked outside the Academy and argued in a different direction, incorporating aspects of empiricism into the basis for evaluating knowledge, but without the insistence on experience as the absolute standard of it. Sextus' empiricism was limited to the "absolute minimum" already mentioned - that there seem to be appearances. This basic thought of Pyrrho's he twined into lengthy arguments, some of them directed against the Academicians. They affirmed knowing that one did not know, and Sextus pressed them on just how they knew that. The common anti-skeptical argument is that if one knows nothing, one cannot know that one knows nothing, and so may know something after all. It is worth noting that such argument only succeeds against the complete denial of the possibility of knowledge. Considering dogmatic both claims to know and claims not to know, Sextus and his followers claimed neither. Instead, despite the apparent conflict with the goal of ataraxia, they claimed to continue searching for something that might be knowable. Their general method remained anthropological and relativist: highlight disagreement and confusion about the big issues, shoulder the burden of proving that knowledge exists onto the dogmatists, and live a quiet life.
In the centuries to come, the words Academician and Pyrrhonist would often be used to mean generally skeptic, ignoring distinction between denial of knowledge and avoidance of belief.
In the ancient east
Buddhism offers a wellspring of skepticism that is little known in much of the West. However, it differs substantially from western philosophical skepticism in several ways:
- Buddha is said to have touched the earth at the time of his enlightenment so that it could witness his enlightenment. In this way, Buddhism does not claim that knowledge is unattainable.
- Buddhism places less emphasis on truth and knowledge than western philosophical skepticism. Instead, it emphasizes the goal of Bodhi, which, although often translated as enlightenment, does not imply truth or knowledge.
- At least in its manifestation of Nagarjuna's texts that form the core of Madhyamaka, the anti-essentialist aspect of Buddhism makes it an anti-philosophy. From that stance, truth exists solely within the contexts that assert them. So, for example, although collaborative games such as scientific contributions to technology may have pay-offs, they are no more or less inherently true than the views and ideas of the Azande, known for their Magical thinking.
Schools of philosophical skepticism
Philosophical skepticism begins with the claim that the skeptic currently does have knowledge. Some adherents maintain that knowledge is, in theory, possible. It could be argued that Socrates held that view. He appears to have thought that if we continue to ask questions we might eventually come to have knowledge; but that we didn't have it yet. Some skeptics have gone further and claimed that true knowledge is impossible, for example the Academic school in Ancient Greece. A third skeptical approach would be to neither accept nor reject the possibility of knowledge.
Skepticism can be either about everything or about particular areas. A "global" skeptic argues that he does not absolutely know anything to be either true or false. Academic global skepticism has great difficulty in supporting this claim while maintaining philosophical rigor, since it seems to require that they insist that nothing can be known—except for the knowledge that nothing can be known. They have not yet demonstrated how it is they actually know that nothing can be known.
Some global skeptics avoid this problem by maintaining that they merely are "reasonably certain" (or "believe") that skepticism is true, while never asserting that skepticism itself is "known" to be true with absolute certainty. For such skeptics, while an argument may be advanced in support of skepticism, the argument does not conclude or imply that it (the argument itself) is indubitable. A self-referential version (holding that skepticism is subject to skepticism) is consistent with it's own tenets, however concedes that skepticism can never be "proven".
A Pyrrhonian global skeptic labors under no such constraint, since he only claims that he, personally, does not know anything and makes no statement about the possibility of knowledge.
Local skeptics deny that we do or can have knowledge of a particular area. They may be skeptical about the possibility of one form of knowledge without doubting other forms. Different kinds of local skepticism may emerge, depending on the area. A person may doubt the truth value of different types of journalism, for example, depending on the types of media they trust.
Epistemology and skepticism
Skepticism is related to epistemology, or the question of whether knowledge is possible. Skeptics argue that the belief in something does not necessarily justify an assertion of knowledge of it. In this skeptics oppose foundationalism, which states that there have to be some basic beliefs that are justified without reference to others. The skeptical response to this can take several approaches. First, claiming that "basic beliefs" must exist amounts to the logical fallacy of argument from ignorance combined with the slippery slope. While a foundationalist would use Munchhausen-Trilemma as a justification for demanding the validity of basic beliefs, a skeptic would see no problem with admitting the result.
This skeptical approach is rarely taken to its pyrrhonean extreme by most practitioners. Several modifications have arisen over the years, including the following:
Fictionaism would not claim to have knowledge but will adhere to conclusions on some criterion such as utility, aesthetics, or other personal criteria without claiming that any conclusion is actually "true".
Philosophical fideism (as opposed to religious Fideism) would assert the truth of some proposition, but does so without asserting certainty.
Some forms of pragmatism would accept utility as a provisional guide to truth but not necessarily a universal decision-maker.
Motivations for external world skepticism
David Hume offers one argument as to why anyone would want to question the reliability of perception. Hume's argument basically says that we can't know anything about the external world, because to know that, we would have to know that there is a connection between our sense-data and the external world that they are supposed to represent. But the only thing we have contact with are our sense-data; we can never know anything in the external world except by first knowing our sense-data. But then we have no way to prove the connection between our sense-data and the external world. So we have no way to prove that our sense-data do represent any external world -- and that is to say that we have no way to prove that perception is reliable.
In addition to Hume's argument for external world skepticism, there is another more famous argument. This is Descartes' famous dreaming doubt, and it goes like this: Descartes was writing one evening in his room, and he thought to himself (paraphrasing very loosely): What if I am asleep in bed right now, and only dreaming that I am awake, and writing? Isn't that at least possible? Then he said, well surely, I can tell when I am awake and when I am asleep. I can tell the difference between wakefulness and a dream. All sorts of strange things happen in dreams; I pass unaccountably from scene to scene when I'm dreaming; I don't have any long memory of what happened in a day, when I'm dreaming; and so forth. Then Descartes said: Haven't I had those very thoughts in some of my dreams? Sometimes, when I was dreaming, I was convinced that I was awake! I even tried to test that I was awake, when I was dreaming, and the tests convinced me that I was awake! But I was wrong; I was dreaming. Isn't it quite possible that the same thing is happening to me right now? Isn't it possible that I am dreaming that I can test whether I'm awake or asleep -- and of course, in my dream, I pass the test? So it seems really vivid to me right now that I'm awake -- but in fact, I'm asleep?
Well, Descartes said to himself, I guess there aren't any definite signs, or tests, that I could use to tell whether I'm asleep or dreaming. I could, after all, be dreaming those very tests. I have experience of doing that, thinking that I passed the test for being awake, when really I was only dreaming. So there isn't any way to tell that I am awake now. I cannot possibly prove that I am awake. So, Descartes said to himself, I don't really know that I am awake now and writing in the evening. For all I really know, I could be asleep. That's Descartes' dreaming doubt.
Now we can go on and examine this argument in more detail. For one thing, why does Descartes think that he doesn't know he's awake and writing? Well, he might be asleep. But what difference does that make? The difference that it makes is that his faculty of sense-perception would not be reliable if he were asleep. In other words, if he were asleep, it would seem to him that he is seeing, feeling, and hearing various things; but he wouldn't really be. In that case, of course, his faculty of perception wouldn't be reliable. But Descartes appears to go further than that: he appears to be saying that since he might be dreaming, since he can't rule out the hypothesis that he is dreaming right now, that also means that his faculty of perception is not reliable.
To many people, Descartes' position may seem absurd. Most people simply feel that of course they can tell that they're not dreaming. Here, though, Descartes' could reply that maybe you can, but maybe you're just dreaming that you can tell the difference. If you say you can tell the difference between being awake and being asleep, then you are assuming that you're awake, in which case you're begging the question against the skeptic.
Another common sense sort of response to Descartes' argument is that one can tell that one's sense-perception is reliable, and here's how: When one sees something, like that cow chewing on daisies, one can go over to the cow, touch it, hear it, lean on it, and so forth. That confirms that one really is seeing the cow. In the same way, when one hears something, like a marching band outside, one can step outside, and look at the marching band, talk to the members of the band, and so forth. That confirms that one heard the band outside. Throughout a person's life they've had so many experiences like this that they are practically certain that, in the more obvious cases anyway, their faculty of perception works -- it's generally reliable.
Descartes' skeptic will reply to this in much the same way as the previous objection: You might just be dreaming that you are touching, hearing, and leaning on the cow. That marching band might just be part of a dream. For that matter you might only be dreaming that your faculty of perception has been generally reliable. If you argue you're not dreaming as your faculty of perception is reliable, then you are once again begging the question. First, you must establish that you're not dreaming, and that's impossible. Thus, you can't know that your faculty of perception is reliable.
Additionally, a sharper skeptic might make another remark about seeing the cow and hearing the marching band. Because, after all, weren't you using sense-perception in order to try to argue that your faculty of perception is generally reliable? Think about that: in order to show that your sense of sight works, you use your sense of sight and other senses; in order to show that your sense of hearing works, you use your sense of hearing and other senses. And it's not like you can avoid that. It would be really bizarre (though some philosophers have actually tried it) to try to argue that your senses are reliable, without making use of your senses. But if you make use of your senses, you are begging the question again. You have to assume, or presuppose, that your senses are generally shipshape before you start using them to prove anything, including whether your senses are generally shipshape.
How can you prove that perception is reliable without using your senses? That seems impossible. But how can you use senses without assuming that perception is reliable? If you do that then you're arguing in a circle, you're begging the question. So what's the upshot? That you can't prove that perception is reliable. If you try, you beg the question, and question-begging is a logical fallacy.
Notice that this is actually a third skeptical argument, distinct from Hume's and Descartes', although it is related to both. Hume said you can't prove that your sense-data represent the external world; Descartes said that you can't even prove that you're not dreaming; and this third argument says that you can't prove that perception is reliable without assuming that your senses are reliable and thereby begging the question at issue.
Objections to philosophical skepticism
First of all, in all three arguments -- Hume's, Descartes', and the circularity argument -- the claim is made that we can't prove something or other. We can't prove that sense-data represent an external reality. We can't prove that we're not dreaming. We can't prove that perception, or memory, is reliable. But now ask yourself: just because you can't prove something, does that mean that you don't know it? Or that you aren't justified in believing it? Take Descartes' dreaming doubt as an example. Suppose you're convinced that you can't prove that you're not dreaming, not without begging the question. And you're even willing to admit that mere very slight possibility that you are dreaming right now. However, a non-skepticist might reply, who cares? So what if I can't prove, to Descartes' skeptic, that I'm not dreaming? Who cares if there is a very, very slight possibility that I'm dreaming right now? Does that really matter to my knowledge-claims?
Now, Descartes himself thought it definitely did matter. Descartes wanted absolutely certain knowledge -- knowledge beyond any doubt. And so he thought that if you can raise the smallest doubt about something, then you don't really know it. For example, the dreaming doubt raises the very small possibility that you are not actually reading this article right now; you might be dreaming; and so Descartes would say (at that point -- later he thought he refuted this skepticism) that you don't know you're reading this right now.
So this forces us to ask ourselves: Do we have to have absolute certainty, lacking any doubt whatsoever, in order to have knowledge? That would be the absolutely strongest grade of justification possible. And then we would be saying that knowledge is not just sufficiently justified true belief, but certainly true belief.
Many philosophers don't think that such a strong degree of justification is necessary for knowledge. After all, they claim, we can know what the weather is going to be like, just by reading the morning forecast. Sometimes we're wrong; but if we're right then we have knowledge. So they are not particularly worried if they can't prove that they're not dreaming. They think it's extremely unlikely that they're dreaming, and they think they're perfectly well justified in thinking they're awake. And they don't have to know with absolute certainty that they're awake, of course, to be well-justified in believing they're awake. Note too that Descartes himself rejected his skeptical doubts in the end.
Here's a second thing you might observe about skepticism: if the skeptic makes absolute certainty a requirement for knowledge, then you could reply that this observation should be applied to skepticism itself. Is skepticism itself entirely beyond doubt? Isn't it possible to raise various kinds of objection to skepticism? So it would appear; but then no one can know that skepticism is true. So then the skeptic can't know that skepticism is true. But this is actually a bit of a weak reply, because it doesn't really refute skepticism. The skeptic, after all, may be perfectly happy to admit that no one knows that skepticism is true. The skeptic might rest content saying that skepticism is very probably true. That's not the kind of claim that most non-skeptics will be happy to allow.
A third objection, which especially applies to the circularity argument, comes from the common-sense Scotsman, Thomas Reid. Reid argued as follows. Suppose the skeptic is right, and perception is not reliable. But perception is just another one of my cognitive processes; and if it is not reliable then my others are also bound not to be reliable. All of my faculties came out of the same shop, he said; so if one is faulty the others are bound to be as well. But that means that the faculty of reasoning, which the skeptic uses, is also bound to be unreliable too. In other words, when we reason, we are bound to make errors, and so we can never trust the arguments we give for any claim. But then that applies to the skeptic's argument for skepticism! So if the skeptic is right, we should not pay attention to skepticism, since the skeptic arrives at the skeptical conclusion by reasoning. And if the skeptic is wrong, then of course we need not pay attention to skepticism. In either case, we need not take skepticism about the reliability of our faculties seriously.
The form of Reid's argument is a dilemma, like this: if P, then Q; if not-P, then Q; either P or not-P; therefore, in either case, Q. Either the skeptic is right, in which case we can't trust our ability to reason and so can't trust the skeptic's conclusion; or the skeptic is wrong, in which case again we can't trust the skeptic's conclusion. In either case we don't have to worry about skepticism!
But Reid’s argument assumes that reasoning is a ‘faculty’ and that the skeptic uses it necessarily. So, where are the reasons of these assumptions? Can they not be refuted? The argument has dogmatic premises and they may be wrong.
see more Responses to skepticism
- Sextus Empiricus
- Problem of the criterion
- Five minute hypothesis
- James Randi
- Abuses of skepticism
- Skeptical hypothesis
- Here is one hand - a response to skepticism
- Excerpts from the "Outlines of Pyrrhonism" by Sextus Empiricus
- Stanford Encyclopedia of Philosophy entry
- Refutation of external-world scepticism. On-line version of two recently published books by philosopher Olaf M. Müller (in German)
- Article: Skepticism and Denial by Stephen Novella MD, The New England Journal of Skepticism
- Classical Skepticism by Peter Suber.
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