I have an argument outline for rejecting hard-skepticism, though I'm not quite sure if it fully works and I was wondering if it's actually interesting, or just rubbish.

Firstly, I'll lay out the 3 forms of hard-skepticism I'm aware of:

  1. Descartes’ Malevolent Demon - No external world exists, but my perception of one is the result of a malevolent demon who has built a fully formed illusion of one.
  2. Brain in a Vat - None of my perceptions correspond to the way the world is, but rather are the results of a scientist who has my brain in a vat and triggers all of the proper neurons to provide the illusion of my world.
  3. Nick Bostrom’s Simulation Hypothesis - “At least one of the following propositions is true

(i) The fraction of human-level civilizations that reach a posthuman stage (that is, one capable of running high-fidelity ancestor simulations) is very close to zero.

(ii) The fraction of posthuman civilizations that are interested in running ancestor-simulations is very close to zero.

(iii) The fraction of all people with our kind of experiences that are living in a simulation is very close to one."

Therefore, it’s possible, if not likely, that we are living in a simulation.

So, let us assume Skepticism and say that our perceptions do not correspond to present reality. If this is the case, then according to all of the skeptics, our false perceptions have to come from somewhere (an external source). If we take Manipulator A to be the one providing the illusion of reality (i.e. the mad scientist in the brain in a vat, or the human-like species running simulations), then Manipulator A should also have the exact same argument to question her reality. (I should point out that Manipulator A does not need to be a conscious being. In fact, she could simply be my body. The only requirement for her is that she lies external to “I”.) That is, there’s no reason for “I” to be the only one skeptical that “I”’s perceptions are real. Even if Manipulator A does not question, there’s no reason for the arguments to not apply to Manipulator A (Similar to how the arguments of skepticism apply to animals even if they don't have the capacity to be skeptical). In fact, the arguments flow upstream to any creature capable of manipulating. Then, in turn, Manipulator B would be the one providing the illusion to Manipulator A. However, Manipulator B should also question her reality and so on…

However, at a certain point we know that somebody along the chain is actually experiencing reality as it stands (otherwise, nobody would experience anything real and we would enter an infinite regress of illusion. So, because we know that there is something real and that this real thing is what allows for all representation, it must be that at least somebody is experiencing it). So, let’s take this person to be Manipulator Z. But, Manipulator Z is bound in conceivability to that which she experiences. So, the only illusions that she can provide to Manipulator Y are permutations of actual things (that is, take reality to be the unordered set of all things that exist, then the illusion can be comprised only of some subset of that set). In turn Manipulator Y’s illusion must be a permutation of her reality...and so on. Until we get to “I” who experiences an illusion that is based on the reality of Manipulator A which still all comes from actual reality. This leads us to the rather strong conclusion that we cannot experience anything that lies outside the realm of reality. That is, if we are experiencing it, it must be some part of reality.

Does this work? Thanks in advance!

  • No, your argument is not compelling. "According to all of the skeptics, our false perceptions have to come from somewhere (an external source)" is false, skeptics reserve judgement on whether "perceptions" come from anywhere at all, let alone an "external source", they also doubt that "reality" is a meaningful concept. Assuming that our concepts, reasoning, and apparently even some physics, apply to your "manipulators" skeptics will also doubt. There is no logical problem with "infinite regress of illusions", and "bound in conceivability to permutations" claim is doubtful even to non-skeptics.
    – Conifold
    Jan 4, 2017 at 0:37
  • @Conifold None of the Skeptics mentioned in the question have reserved judgement on whether our 'perceptions' come from anywhere at all. In the first example they come from a malevolent demon, in the second a mad scientist, and in the third a human-like race, so it is not entirely fair to dismiss the argument on grounds it never claimed to cover. Also, that Skeptics doubt 'reality' or that we are bound in conceivability by our reality, or that they have no problem with the infinite regress of illusions' does not negate the argument without begging the question.
    – user22791
    Jan 6, 2017 at 9:08
  • @Isaacson The argument is supposed to work against "hard skepticism", examples mentioned are just colorful illustrations to give an idea. And by assuming what they doubt doesn't it itself beg the question?
    – Conifold
    Jan 7, 2017 at 21:58
  • @Conifold My point really was that I think a more constructive criticism would have been to admit that the issues raised were pertinent to the examples given but the examples given do not represent the whole of Hard-Skepticism. Not only does this do more justice to the argument, but it highlights how Academic Skepticism at least runs into difficulties when trying to speculate a manner in which Skepticism might develop a hypothesis.
    – user22791
    Jan 8, 2017 at 7:53

2 Answers 2


Firstly, your examples represent a sub-set of Skepticism or a set of theoretical arguments or hypotheses. Your argument as written does indeed challenge the common sense understanding of these hypotheses, and present a way in which one could be justified in believing that what we are experiencing is some form of true reality, but this does not encompass the whole of Hard-Skepticism.

Your argument presumes a Realist stance (i.e that there is a "real" world independent of us which we can 'discover'). Much of Skepticism, such as Kant, is based on a belief that there is no 'real' world independent of our own minds. As such the difference between manipulator Z and manipulator A would be an arbitrary one as both are experiencing their own thoughts, this would render the argument redundant, so I will continue from a Realist position.

Your argument overall is generally accepted for the arguments of Skepticism you outline (known as Skeptical Hypotheses). Bostrom himself discusses the possibility of an inifinate series of simulations, each running the one below it. It is a form of infinite regress, where the Skeptic simply has to respond to any statement of apparent knowledge with "...but how do you know x", in your example, constantly saying "...but how do you know manipulator A,B etc. is not also in a simulation".

The philosopher John Williams wrote "The regress of justification of S's belief that p would certainly require that he holds an infinite number of beliefs. This is psychologically, if not logically, impossible. If a man can believe an infinite number of things, then there seems to be no reason why he cannot know an infinite number of things. Both possibilities contradict the common intuition that the human mind is finite"

Peter Klein provides a reasoned argument in favour of infinitism in a chapter titled "infinitism" in the Routledge Companion to Epistemology, but here he is arguing in favour of infinitism as a response to Pyrrhonian Skepticism (the only one he sees as viable), not as a form of Hard-Skepticism in the sense I think the OP is intending.

Both approaches (and even to a certain extent the Anti-Realist stances) are resolved by a pragmatic application of the Scientific Process as outlined by Popkin. In such an approach we acknowledge there is an infinite regress of doubt, but sees this as a reason to reject Academic Skepticism in favour of a form of justified uncertainty. We have hypotheses which, so long as they continue to provide us with useful predictions, we can say are true, but if at any time (as Bostrom suggests) a window pops up saying "You are in a simulation, click here to exit", we would have to form a new hypothesis. In this way Skepticism does not prevent us from continuing to form and use new hypotheses.

  • Minute point, but I was under the impression that Kant's skepticism, that is Transcendental Idealism, differs from say Berkeley's version in that it posits that there is an actual world existent independent of I. What exactly that means is obviously very ambiguous, but I just wanted to ask about that one phrase. Jan 8, 2017 at 16:47
  • @user5407287 Yes, Kant's response to Berkely's immaterialism was to posit a real world, but only one, the knowledge of which, is within our minds and so distinct form our experience of it. The reason I dismissed both he and other anti-realists (like Berkeley) is that in both cases, the Manipulator's version of reality (from which they draw to create their simulation) would not necessarily be 'actual' reality, and so would not lead to your conclusion in the second to last paragraph.
    – user22791
    Jan 9, 2017 at 8:00

let us assume Skepticism and say that our perceptions do not correspond to present reality

This, from the outset, assumes the existence of a "present reality", which undermines the rest of the argument.

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