I like to believe one can't be 100% sure of anything, for one can't be 100% sure their brain functions correctly (because if it doesn't, it may mistake itself as functioning correctly as a result). Is there a name for and/or existing material on this theory?

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    @JohnAm No - the OP might be pugged into the Matrix, with an Evil AI make them think that they are doing all of these actions. Oct 27, 2015 at 19:37
  • @ Alexander S King You are saying something. But according to radical skepticism you can't really say it. So at the end "you" and radical skepticism says nothing at all.
    – John Am
    Oct 27, 2015 at 19:50
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    @JohnAm "according to radical skepticism you can't really say it". This is incorrect. Radical skepticism only claims that you can't know if you really say it.
    – user2953
    Oct 27, 2015 at 20:00
  • There is a nice ring of paradoxical self-reference to "Am I asking this question?" similar to "This sentence is false". Logicians made a lot with the Liar, perhaps there is something to Puzzler too.
    – Conifold
    Oct 27, 2015 at 20:19
  • Actually, for Sextus Empiricus, you shouldn't be sure that you don't know whether or not you said it. You should suspend judgement until someone cares, and then act as if they are right, just for your own peace of mind. Bothering to consider it, before knowing it is mandatory is already too arrogant for a real skeptic. And of course you can't get to the knowing it is mandatory point without bothering to considering it. So, Zen.
    – user9166
    Oct 27, 2015 at 20:22

4 Answers 4


I am going to disagree with the "radical skepticism" label. "Not 100%" is very far from "most likely impossible". That certainty is never justified can also mean that it is 99% justified 99% of the time, and I would call that rather overconfident. Depending on specifics OP stance can describe a variety of positions including Quine's empirical holism for example: any claim is subject to future revision in the face of recalcitrant experience, there are no a priori certainties. About 50% of contemporary analytic philosophers subscribe to naturalized epistemology, and they are hardly radical skeptics.


Radical skepticism is the term you are looking for. Descartes Meditation is an early work that starts from this position.


The name for this position is radical skepticism: the idea that no knowledge will ever be certain. DesCartes tried to disprove it with his "I think therefore I am", Hume talks about it. It is one of the central problems of epistemology.


Pyrrho got there long before Descartes, and stayed in the vein for a longer time before betraying its basic principles. Sextus Empiricus' rearrangement of Pyrrho is the closest thing we still have.

Descartes only wishes he could manage to be a radical skeptic. I don't think the natural exit point from true radical skepticism involves three separate proofs of God, and all the other trappings of Descartes.

And as for all the disparaging comments. Bear in mind that major world religions, including branches of Hinduism and Buddhism think it is important to be radically skeptical, at least on a theoretical level.

  • Question everything does not equal do nothing. 1) There is a whole continuum of productive interpretations of radical skepticism when it is rolled up in these faiths from 'always keep an open mind' to 'this is all evil trickery, hide from the world'. (You seem to imagine it always means the latter.) 2) Some religions are actually pretty rational compared to what philosophers say. (Zombies? really? Get over it.)
    – user9166
    Oct 27, 2015 at 20:42