Universal Skepticism seems to boldly claim certainty in the knowledge that knowledge is impossible. The obvious contradiction here is that if they really believe their own theory, it should force them to conclude that there is no way to know that the theory is true, because the very nature of their theory says that knowledge is impossible. This should then open the door to other arguments, since now a universal skeptic is forced to conclude that they have no way of knowing if knowledge is impossible, so they have no reason to put their somewhat arbitrary skeptical beliefs above any others. They should believe what has the the best justification, even if certainty can't be guaranteed, as opposed to only believing that they know nothing.

Would't this really just mean that they are no longer universal skeptics?

  • This is sort of the opposite of "can God create a rock so heavy that he can't lift it". If you assume something is knowable, you can use Godel's Incompleteness Theorem: there is a system of knowledge that can prove itself incomplete.
    – user935
    Dec 29, 2016 at 16:56
  • Universal/Global skepticism isn't a certain claim, it is a belief. It is the belief that knowledge is impossible, which is based on the impression that no one seems to know anything for certain. If knowledge is impossible, there is no way of knowing it (otherwise it would contradict this very assertion). Apr 18, 2021 at 13:30

2 Answers 2


I think the skeptic's claim is more accurately stated in terms of logical systems. The claim is merely that there are no logical systems that don't depend on some basic, fundamental assumptions (axioms) as a starting point. Then you have the problem of proving the axioms, which you can't do with the same logical system that takes those axioms as a given. It does, in fact, seem to be the case that knowledge of any kind will require some assumptions.

I think the better counter argument is to justify the axioms in some way. For example, perhaps some axioms precede knowledge and are hard wired into the rules of the universe.

Personally, I view evolution from 'inanimate objects' to 'sentient beings' as the hook that connects the laws of nature to the necessary assumptions required to posses any knowledge. In other words, knowledge could be viewed as a physical correlation between brain-state and the environment.

  • This is very interesting, but I don't think it really solves the problem I brought up. For example how could a universal skeptic deny that they are experiencing something that they seem to be experiencing. To give a specific example, how could he is experiencing sight. Sure, they could say something like "what does sight mean", but that isn't really the question. Or more basically how could they deny that they are having experience. There do seem to be fundamentally true and undeniable starting axioms, and the universal skeptic would have to explain how those can't lead to more knowledge.
    – monster319
    Dec 30, 2016 at 11:24
  • I wasn't aware that skeptics claim they are not having experiences. Dec 30, 2016 at 14:57
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    Axioms imply things. The issue is how do u know if the axioms are true or really, how could you prove the axioms without the use of the axioms themselves. Dec 30, 2016 at 14:59
  • "It does, in fact, seem to be the case that knowledge of any kind will require some assumptions." Of course it does. How are you going to justify knowledge claims without assuming something in the first place? I can claim to know something without actually knowing it. And I may think I'm certain of something, even though I objectively am not. Without assumptions, no knowledge claims can be evaluated. Apr 18, 2021 at 2:25

If a universal skeptic really needed to claim something, she would indeed be opening her stance to self contradiction. However, a universal skeptic need not claim anything, much less "boldly claim certainty in the knowledge that knowledge is impossible". The skeptic is characterized by disbelieving, not by believing or claiming anything. She need not claim anything, not even that knowledge is impossible. Jill does not need to claim anything, in order to cast doubts on Jack's claims. Jill just needs to show that Jack's justifications, for his claims, are flawed, by Jack's own standards.

Therefore, universal skepticism need not be self defeating.

  • Knowledge is or is not possible. The statement you're talking about is "Nothing can be known except this." Knowledge may be possible, but no objective knowledge can be confirmed without appealing to assumptions. Apr 18, 2021 at 2:32

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