A Refutation of Skepticism

Philosophical skepticism is notoriously difficult to refute. I am not speaking of popular skepticism, as defined by magazines such as Skeptical Inquirer and Skeptic. These are only skeptical of certain things, generally are not skeptical of the issues they support, and hold that knowledge is possible. 

Philosophical skepticism is more rigorous, holding that ultimately we can’t know anything. Ancient Greeks such as Pyrrho of Ellis took skepticism to a rigorous level, doubting whether we can know anything, including whether or not we are doubting. Radical skepticism presents questions such as “It might be that we are a brain in a vat, being fed sensory data by an alien via a complex machine.”  Or “it could be that we are halucinating” or “It could be we are being deceived by an evil demon.”  We can’t just say that this is absurd, for the mental game here is to logically refute it, which is notoriously difficult. All the skeptic has to do is say “It could be an illusion” and leaves us with the problem of positively refuting it beyond all doubt. As silly as this may seem at first glance, otherwise intelligent people have based their lives on the basis that no one can be sure of any meaning. The comedian Steve Martin went into comedy because he could not find anything meaningful in life, and felt that no one is able to be sure of anything meaningful in life.  

So we are presented with a gnarly problem, similar to the Buddhist pantheist, who says that all sensory data is an illusion.

But there are some good refutations. First, all claims that we can’t know ultimately are self-refuting, saying that we know we can’t know. Any attempts to show this self-refutation wrong ends in either another self-refutation or nonsense.  And nonsensical claims cannot be responded to, for they make no claim.
Second, all skeptics appeal to sensory data to claim that we can’t trust sensory data, which is another self-refuting claim. Skeptics say we can’t trust sense data, yet they use sense data to try to prove their case that we can’t trust sense data.
Third, author Peter Klein in his book Certainty claims skepticism can be absolutely refuted if the following can be proven: 1) There is no good reason for believing that knowledge of p is always false, and 2) there is good reason for believing that knowledge of p is sometimes true. Thus, meaning is established, at least some of the time. Fourth, all claims that we might be deceived due to dreaming or by halucinating imply that we cannot tell the difference between those things and reality. But there is a fundamental sense difference between dreams and reality, or else we wouldn’t have two words to name them. If we can’t tell the difference between dreaming and reality, how is it that we have made a distinction enough to use two different names?  There must be some fundamental distinction between them, and we must be able to tell them apart, or else we wouldn’t have two names with two meanings.

Ultimately, the radical skeptic cannot make a claim that holds up. Skepticism is refuted, and absolute knowledge is established.


About humblesmith

Christian Apologist & Philosopher
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12 Responses to A Refutation of Skepticism

  1. dark says:

    I think you have done a good job of refuting absolute skepticism but I don’t think that alone proves absolute knowledge is true. Are there other possibilities?

    The radical skeptic would claim even the truth of whether his own belief, that truth cannot be know, cannot be known. It is a paradoxical position to be sure.

    You’re arguments seem to agree that we can know truth but we can’t necessarily be absolutely certain that which we know is the truth.

    Is it possible there is truth but we can only be ever more sure of it’s likely hood not that it is absolute?

    • humblesmith says:

      Absolute knowledge of truth can be established, at least in some cases. We may not be able to determine truth in all cases, but we can in some.

      We can know that it is true that the laws of logic apply to all meaningful statements. Laws of thought, such as the law of identify (A is A) and the law of noncontradiction (A is not non-A) hold true in all meaningful statements, for anyone who tries to deny them must use them in their denial.

      You are correct that the severest of skeptics, such as some of the ancient Greeks (followers of Pyrrho), held to such a radical skepticism as you describe. But their claims are absurdity. Trying to say that we cannot know that we cannot know, and make any sort of conclusion, is on the level with trying to say “blue april non-banana.” It’s just meaningless, and certainly does not prove anything or make a truth statement which could be refuted or affirmed.

      That we cannot know some things is a truth that we can know for certain. This does not mean that all things are unknowable….in fact, it is a statement that we know for certain is true.

      As to your last question, look at it this way. If we were to conclude that “There is truth, but we cannot be absolutely certain of it. We can only be ever more sure of its liklinood.” Such a statement is either true or not. Whether we affirm it or deny it, we know something for certain (that it is true or false.) Therefore in an absolute sense, we affirm that we can indeed know some things for certain.

  2. Diogenes says:

    I disagree. The statement a = a is only 100 percent true if its referring to itself. (a IS a). thus, the statement “A=A” depends on our conception of a universe in which things such as matter and reality, existence and reflections of events are real. IF, for example, the universe is such that nothing (thoughts, items, etc) are REAL, in our sense of the word, even the statement a=a is incorrect. remember, a skeptic is free to reduce the claim that knowledge is possible to the absurd using a = a type arguments. if she can show that they lead to a contradiction, then a = a reasoning is invalid.

    • humblesmith says:

      You either hold your statements to be true, or not. This exhausts the possibilities. If you hold the statement you just made to be true, then you have stated something that we can know, and philosophical skepticism is refuted. If you hold that the statement you just made is not true, then “a is a” logic holds, and we can know something.

      Strictly speaking, Aristotle’s law of identity, a is a, does not depend on a real world existing. The concept applies in pure analytic logic. If the number 4 is not the number 4, we can have nothing meaningful. This is true regardless of whether four of anything actually exists anywhere. If you are suggesting that thoughts do not have to identify with themselves, then the skeptic cannot make any claims, let alone the claim that we cannot know anything. Again, if the statements you just made are not the statements you just made, you’ve said nothing. If the statements you just made are themselves and have any meaning, then skepticism is refuted.

  3. Skeptic says:

    [this reply has been edited for brevity by the blogger. The original reply was very long and off-topic. ]

    The main principle the Skeptic uses is that of doubt: in Descartes’ case that of methodological doubt. Descartes poses his main argument as such; if one has knowledge of their perceptions than one has knowledge that they are not being deceived, one does not have knowledge that they are not being deceived therefore one does not have knowledge of their perceptions. (William 146)
    This basic argument is valid through modus tollens. So, what is Descartes doing throughout this argument? He is creating doubt. Practically, Descartes is asking one very essential question, how do we know what we know? Since we are using absolute certainty as the standard for knowledge, this question becomes a very hard one to answer.
    Now, everyone has many perceptions everyday. They perceive “blueness” in the sky, they perceive the car that they drive in every morning to get to work, and they even perceive the smells of everyday life such as the pot of coffee they brew every morning. Of these perceptions, Descartes asks one defining question, can one acquire knowledge through the senses? At this point, the average person would reply with an astounding yes, due to the fact that these perceptions are the only way one can experience the world. This is where Descartes methodological doubt really starts to take off.
    One does have to admit, and therefore believe, that their senses can be deceived from time to time in cases such as a mirage or an optical illusion. Therefore, deception of the senses is possible. So, what is to say that one is not being deceived on a grand scale every day? What if one is constantly being deceived, by an outside source, all through his life and has no knowledge of it? This hypothetical outside force is whom Descartes refers to as the Great Deceiver or Evil Genius. (Descartes 12)
    Descartes’ Evil Genius plays a large role in his theory of methodological doubt. Let us return to the same man who has a perception of the “blueness” of the sky. A perception of the car he drives to work, and the perception of the smell his coffee pot emits each morning. What if all these perceptions are being created by an evil genius, and none of them actually exist? What if every perception we ever have experienced is nothing more than a figment of our imagination that has been placed there by a great deceiver? This would be very disturbing. To think that every perception we ever had is nothing more than deception. Once one has come to the realization that our perceptions could in fact be deceptions, one must strive to see if there is in fact a truth or perception that could not possibly be a deception. For if there is any possibility that one of our perceptions could in fact be a deception than one does not have knowledge of that perception.

    Even further then the deception of ones perceptions in details such as color, this uncertainty can lead one to the point at which they question the actual existence of things; for instance, the existence of the man’s car. Through the same line of reasoning we can arrive at the conclusion that the man does not in fact know that his car exists.

    The senses we are given are the only faculty each and every person has to interact with the external world, and because we cannot have absolute certainty through our senses we have no knowledge that any thing in the eternal world truly exists. People may question how one could be under this great deception and not realize that they are in fact being deceived. For instance, when one experiences a dream or mirage the illusions may not feel like real life, itself. (13) The images are not as clear and, many times when people are experiencing dreams or mirages the content does not feel as distinct or real. The problem with this analysis is twofold. First, many times when people are experiencing dreams or mirages they do in fact feel real. Only afterwards do these experiences feel less genuine, or does one question their reality. Secondly, one is presupposing that the reality we live in is in fact real and not a deception.
    If every person were experiencing an eternal deception than the eternal deception would be all they know, so it would obviously feel like the ultimate and most real experience. Just as if one was in an eternal slumber, that sleep would seem like the ultimate sense of reality and perception. So, to say that one would feel the difference between real life and deception is disingenuous, and putting way to much trust in faulty senses. (Velasco)
    To really feel the weight of Descartes’ argument, one must fully understand the fact that the senses, which we treat all our life as reliable, are useless in achieving that of absolute certainty, knowledge, in regards to existence.

    Through this we realize that we cannot arrive at absolute certainty in regards to causal connections, but neither can we arrive at absolute certainty in regards to external existence. Knowing this places one into a new state of mind.

    • humblesmith says:

      Did you even read this post? I’m assuming not, since all you have done is posted the majority of a paper you have written into my blog. Sorry, but my blog is not a place for such things.

      But in response, you are guilty of my first and second points, and did not respond to the third. You claim that you know you cannot know, which is self-refuting, and you use sensory data to prove that sensory data is faulty. You are certain that you cannot have any certainty about external existence. This is indeed a new state of mind.

      As for our friend Descartes, I would encourage you to go back and read his original work, Meditations, and read it all the way through. In the end, he tells us that he did not actually doubt his senses, for to do so would be absurd, but is merely doing a thought experiment, trying to show the existence of God is more sure than anything else we know.

      Forther, as Aquinas taught, we are indeed not deceived by our senses. We sense something, cross-check our perceptions with our other senses, then make a judgement about the object. Our judgements can sometimes be faulty, but our sense perceptions are accurate.

  4. AJ says:

    Hi, I agree with your post entirely but I was wondering how you would respond to someone who says we can only know necessary truths such as the law of non contradiction but nothing else including the existence of the outside world. It would appear to me that the statement that we can only believe necessary truths is not a necessary truth and thus it is self defeating. But, im not sure that this is coherent, do you think it is? Also do you think that since it is necessary that we obtain absolute truth it means that all of these brain in a vat scenarios are impossible on strictly logical terms based on the fact that we could never obtain absolute truth or they lead into contradictary statements or are your arguements presented above only proposed to make radical skepticism rationally untenable much like Plantingas evolutionary arguement against naturalism rationally untenable?

    • humblesmith says:

      If someone were to tell me that it is not possible to know the existence of the outside world, I would ask for proof. My question would be “How can you be sure of that?” Their answer would either be some claim that we cannot trust sensory perception or a claim based purely on mental reasoning without dealing with sensory perception. As the post says, if they use examples of sensory perception to try to prove that we cannot trust sensory perception, then they have made a self-refuting claim. Usually these types of claimes sound like Descartes’ appeal to our senses being fooled to try to prove that we cannot trust our senses. But like Descartes, the only way we would know that our senses are fooled is to appeal to something we know for sure about our senses.

      Claims that start in the mind and try to conclude that we cannot know that the outside world all seem to only be able to draw conclusions about reasoning, not the external world. There is no way to make a conclusion about the outside world without making references to the outside world. Once we do so, we are no longer just in the mind, but also dealing with sense perceptions of the outside world again. Think of it…..if you were purely in the mind, then how could you make a claim aboout not knowing the outside world without evaluating the data that is coming into the mind from outside the mind? Once we have data coming into the mind from outside, we have the same problem as I explained about sense perception.

      In reality, these claims to not know the real world are actually saying, in effect, “I have evaluated what I can perceive about reality, compared it to what I know to be true about reality, and concluded that we cannot know anything to be true about reality.” When phrased this way, the absurdity becomes clear. We cannot prove something false until we know a truth to compare it to.

      All of the brain-in-a-vat scenarios are defeated by the same points I made in the post about halucinations and Klein’s claims about certainty. These scenarios are saying to us, “prove to me that I’m not a brain in a vat.” Our response is thus: We have no reason to believe that it is always true that we are a brain in a vat, and some evidence that we are not a brain in a vat. Therefore given enough situations, there are some instances when we can be certain that we are not a brain in a vat. All we need is a single instance of certainty to refute these scenarios.

      On a practical level, it is just not reasonable to conclude something like these philosophical games being true. Even the king of the skeptics, David Hume, claimed that eventually we have to put our little game back in the closet and go on to living life in the real world. The biggest, strongest refutation for strong skepticism is that it cannot be lived on a daily basis. Anyone that says we cannot know the outside world is forced to live as if the outside world were actually there……they cannot live the skepticism that they claim to believe. As I have said, there’s no philosophical skeptics in major league baseball, because you either you deny your skepticism and duck, or you get hit in the head with a 90 mph fastball and die. Either way, no skeptics in the major leagues.

      Also, as Walter Martin used to say, “If I’m talking to you, and you’re not there, one of us is crazy.”

      All of these goofy philosophical problems start with analytic philosophy as opposed to a realist philosophy. If we start in the mind, we are forever locked in the mind.

  5. Mat says:

    “All of the brain-in-a-vat scenarios are defeated by the same points I made in the post about halucinations and Klein’s claims about certainty. ”

    Are you sure?

    I know about Putnam’s semantic externalist objections to the brain-in-a-vat, but at the same time I’ve also read responses to that in Sanford C Goldberg’s recent book “The Brain in a Vat” which compiles various recent contemporary papers about the Brain in a Vat scenario, some of which criticise Putnam’s externalism and her arguments against the scenario.

    Or are your objections not actually based on Putnam’s semantic externalist framework but other types of reasoning?

  6. Scalia says:

    A good, succinct refutation.

    I don’t know where to ask this question, so I thought I’d post it here. I’m having a little trouble understanding some of the finer points of Aquinas’ metaphysics. What is the difference between form/matter and supposit/nature? In reading various explanations, I’m getting the same definitions. How does matter differ from supposit, and how does form differ from nature?

    Thanks, in advance, for your assistance.

    • humblesmith says:

      According to Joseph Owens in “An Elementary Christian Metaphysics,” the term “nature” is an abstraction that can be known apart from real being (p.48). So a tree’s nature is not restricted to the physical instance of the tree in the yard. (p.68)The term “supposit” has be existent, something that really acts. “If the individuated nature is considered in abstraction from its being, it is not called a supposit.” (p.152-153). Further, a supposit is complete,a whole, while a form can be incomplete in its nature.

      Matter is potential, and prime matter is pure potential with no mixture of actuality. Form can be distinguished from matter but not really separated. So a formal cause takes matter from potential to actual, Matter would then contrast with nature in that form is the cause of the matter being this specific type of matter. The form of a door causes the wood to be a door, not a floor. I do not see nature being spoken of in the same way as a formal cause.

      So form does not have to be the complete form of a thing, while a supposit does, and matter is potential while nature is an abstraction derrived from an existent thing.

      At least that’s my understanding of it. Good question….I hadn’t thought of this.

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