Are you sure you have hands?

leonardo_aby Massimo Pigliucci

Skepticism is a venerable word with a panoply of meanings. When I refer to myself as “a skeptic,” I mean someone inspired by David Hume’s famous dictum: “In our reasonings concerning matter of fact, there are all imaginable degrees of assurance, from the highest certainty to the lowest species of moral evidence. A wise man, therefore, proportions his belief to the evidence” [1]. Or, as Carl Sagan famously phrased it, “Extraordinary claims require extraordinary evidence” [2]. Oh, and if there is one thing I resent it is being mislabelled as a “cynic,” meaning a naysayer with no sense of humor…

But skepticism (and cynicism, for that matter!) in philosophy is much, much older than that, and has at the least a couple of additional meanings [3]. According to so-called (by Sextus Empiricus, second or third century CE, [4]) “academic skeptics” (because they belonged to Plato’s academy, post-Plato), such as Carneades (214-129 BCE) [5], we cannot have any epistemically interesting knowledge. A different type of skeptic, the Pyrrhonian (named after Pyrrho, 365–ca 275 BCE) denied even that we can deny the possibility of knowledge, a meta-skepticism, if you will. Few modern philosophers are interested in Pyrrhonism, while academic skepticism has a long and venerable tradition, including perhaps most famously Descartes’ “radical doubt” thought experiment, in which he imagined a Machiavellian demon determined to trick him about what he thought he knew. Descartes then asked whether it would be possible, under those circumstances, to actually know anything at all. His answer, of course, was in the affirmative, and took the form of his famous cogito, ergo sum (I think, therefore I am) [6].

There is, of course, a much more fun way to think about the problem of skepticism in epistemology, and that is by using the 1999 scifi move The Matrix as a philosophical thought experiment [7]. The movie famously begins with our hero, Neo, played by Keanu Reeves, living what he thinks is a perfectly normal life, which soon reveals itself to be anything but. Neo, turns out, is much closer to the famous “brain-in-the-vat” (BIV) scenario of modern philosophy of mind (to be precise, he is a body-in-the-vat), with all his “experiences” actually being fed to him via artificial stimulation for the purposes of an evil post-technological civilization of machines that have enslaved humanity.

There is a crucial scene in the movie [8] where Neo’s mysterious mentor, Morpheus (played by Laurence Fishburne) poses the question to Neo of whether he wants to keep living in the “reality” he knows, or if he has the guts to see “how deep the rabbit hole goes.” As we know, Neo chooses the red pill that characterizes the second choice and the movie unfolds from there.

Neo, of course, is initially (properly) skeptical (in the Humean sense) of what Morpheus is trying to convey. The latter might as well have asked his question along the lines of: “how do you know you are not a brain in a vat?” How would you answer that sort of question? Which is another way of asking: have we made any progress against (academic) skepticism?

My discussion here tracks the one put forth in Steup’s broader treatment of epistemology in the Stanford Encyclopedia of Philosophy [9]. We begin with a quick look at the minimal version of the BIV argument:

(1)  I don’t know that I’m not a BIV.

(2)  If I don’t know that I’m not a BIV, then I don’t know that I have hands.

Therefore:

(3) I don’t know that I have hands.

This is a formally valid argument, i.e. its structure is logically correct, so any viable response needs to challenge one of its premises — that is, question what in logic is called its soundness. Before proceeding, though, we must note (as Steup does) that premise (2) is tightly linked to (indeed, it is the negative version of) the so-called Closure Principle: “If I know that p, and I know that p entails q, then I know that q” — a principle that is definitely eminently reasonable, at first sight. The application to our case looks like this: If I know that I have hands, and I know that having hands entails not being a BIV, then I know that I’m not a BIV. But — says the skeptics — the consequent of this “BIV closure” is false, hence its antecedent must be false too: you just don’t know whether you are a BIV or not!

There are, of course, several responses to the skeptic’s so-called “closure denial.” Steup examines a whopping five of them: relevant alternatives, the Moorean response, the contextualist response, the ambiguity response, and what one might call the knowledge-that response. Let’s take a quick look.

A first attack against the BIV argument is to claim that being a BIV is not a relevant alternative to having hands; a relevant alternative would be, for instance, having had one’s hand amputated to overcome the effects of disease or accident. This sounds promising, but the skeptic can very well demand a principled account of what does and does not count as a relevant alternative. Such an account could perhaps deploy a type of approach naturally enough called relevance logic [10], but that would get pretty technical, so I’ll leave it for another time.

Second attack: G.E. Moore’s (in)famous “I know that I have hands” response. This is essentially an argument from plausibility: the BIV goes through if and only if its premises (I don’t know whether I’m a BIV, so I don’t know whether I have hands) are more plausible than its conclusion (I don’t actually know whether I have hands). Which, of course, Moore famously denied — by raising one of his hands and declaring “here is one hand.” But why, asks (reasonably, if irritatingly) the skeptic? To make a long story short, Moore’s counter to the BIV argument essentially reduces to simply asserting knowledge that one is not a BIV. Which, ahem, pretty much begs the question against the skeptic [11].

Third possible anti-skeptic maneuver: the contextualist response. The basic intuition here is that what we mean by “know” (as in “I know that I have hands,” or “I don’t know that I’m not a BIV”) varies with the context, in the sense that the standards of evidence for claiming knowledge depend on the circumstances. This leads contextualists to distinguish between “low” and “high” standards situations. Most discussions of having or not having hands are low standards situations, where the hypothesis of a BIV does not need to be considered. It is only in high standards situations that the skeptical hypothesis becomes salient, and in those cases we truly do not know whether we have hands (because we do not know whether we are BIVs). This actually sounds plausible to me, though I would also like to see a principled account of what distinguishes low and high standard situations (unless the latter are, rather ad hoc, limited only to the skeptical scenario). Perhaps things are a bit more complicated, and there actually is a continuum of standards, and therefore a continuum of meanings of the word “know”? [12]

Fourth: the ambiguity response. Here the strategy is to ask whether the skeptic, when he uses the word “know” is referring to fallible or infallible knowledge. (This is actually rather similar to the contextualist response, it seems to me, though the argument takes off from a slightly different perspective, and I think is a bit more subtle and satisfying.) Once we make this distinction, it turns out that there are three versions of the BIV argument: the “mixed” one (“know” refers to infallible knowledge in the premises but to fallible knowledge in the conclusion), “high standards” (infallible knowledge is implied in both premises and conclusion), and “low standards” (fallible knowledge assumed in both instances). Once this unpacking is done, we quickly reach the conclusion that the mixed version is actually an instance of invalid reasoning, since it is based on an equivocation; the high-standards version is indeed sound, but pretty uninteresting (okay, we don’t have infallible knowledge concerning our hands, so what?); and the low-standards version is interesting but unsound (because we would have to admit to the bizarre situation of not having even fallible knowledge of our hands!).

Finally: the knowledge-that response, which is a type of evidentialist approach. The idea is to point out to the skeptic that the BIV argument is based on a number of highly questionable unstated premises, such as that it is possible to build a BIV, and that someone has actually developed the technology to do so, for instance. But we can deny these premises on grounds of implausibility, just like we would deny, say, the claim that someone has traveled through time via a wormhole on the ground that we don’t have sufficient reasons to entertain the notions that time travel is possible and that someone has been able to implement it technologically. Yes, the skeptics can deny the analogy, but the burden of proof seems to have shifted to the skeptic, who needs to explain why this is indeed a disanalogy. Can someone please get me a red pill?

Now, why on earth did we engage in this, ahem, academic discussion? Because I wanted to give you a flavor of how philosophy makes progress, and why it isn’t particularly fruitful to compare it with progress in the natural sciences (did you see any systematic observation or experiment peeking through the above?). Indeed, I am writing a whole book on this topic, which I will hopefully deliver to Chicago Press by the end of the summer. No, make that I will definitely deliver by the end of summer…

The idea is that philosophy is concerned with exploring conceptual, as distinct from empirical, spaces, which is precisely what we have done above. Indeed, you could go through it again and try to build a concept map [13] to see whether you followed the discussion correctly and to visualize its unfolding. The five responses presented by Steup can be thought of as five peaks in the conceptual space defined by the BIV problem, with other possible responses having been examined and discarded during the long history of the debate (those would be conceptual valleys, to continue the metaphor). Not all peaks are necessarily of the same height — where the height roughly measures how good a given response is, and even the precise position and shape of the peaks may vary over time, as philosophers keep refining them in response to counterarguments from the skeptics.

Moreover, the metaphor should make clear that even to ask the question of what is the true answer to the BIV problem is, in a fundamental way, to misunderstand the whole process. If the BIV question were an empirical one — like “how many planets are there in the solar system” — then it would have one definite answer [14], and a bunch of bad ones. But in conceptual space there often are several reasonable ways of looking at a particular problem (“answers”), and it will not be possible to pare them down to just one. (Another way to put this is to say that conceptual space is wider than, and underdetermined by, empirical space.)

So, what should we then make of (academic) skepticism and its critics? I think the value of the skeptical position is that it fosters epistemic humility: we are really not as smart as we often think we are, and in fact we don’t even have unequivocal answers to very basic questions about knowledge. As for the responses to the BIV problem, the five sketched above represent peaks of different heights in the proper conceptual landscape, and in my mind the ambiguity and the knowledge-that peaks are significantly higher than the rest, the Moore response is the lowest, and the relevant alternative and contextualist options are somewhere in the middle. But I’m sure we can have a discussion about that.

_____

Massimo Pigliucci is a biologist and philosopher at the City University of New York. His main interests are in the philosophy of science and pseudoscience. He is the editor-in-chief of Scientia Salon, and his latest book (co-edited with Maarten Boudry) is Philosophy of Pseudoscience: Reconsidering the Demarcation Problem (Chicago Press).

[1] In An Enquiry Concerning Human Understanding, published in 1748.

[2] A dictum, by the way, which can easily and rigorously be formalized in Bayesian terms.

[3] Here is the obligatory SEP entry, by Peter Klein.

[4] On Sextus Empiricus.

[5] Here is my take on Carneades.

[6] On Descartes’ epistemology.

[7] You can do this and much more by engaging the fun essays in the collection put together by Susan Schneider, Science Fiction and Philosophy: From Time Travel to Superintelligence, Wiley-Blackwell, 2009.

[8] Here it is, for your viewing pleasure.

[9] Epistemology, by Matthias Steup, SEP, 2005.

[10] Relevance logic.

[11] On George Edward Moore.

[12] I know, I know, this is beginning to sound rather Clintonesque. Then again, the former President of the United States did study philosophy at Oxford as a Rhodes Scholar…

[13] On concept mapping.

[14] Well, kinda. The famous “demotion” of Pluto to “dwarf planet” hinges on the rather arbitrary — and in some sense philosophical — question of what counts as a planet and why. Incidentally, and contra popular perception, it was Caltech astronomer Mike Brown who was chiefly responsible for killing Pluto, not my friend Neil deGrasse Tyson. Neil did, however, write a popular book about the story.

273 thoughts on “Are you sure you have hands?

  1. Hi Massimo,

    You just don’t want to give up the scientistic ghost and accept that a purely philosophical argument is, in fact, empirically (i.e., scientifically) unassailable.

    That’s not me at all. I believe all sorts of things on purely philosophical grounds which are empirically unassailable. I could name a few, but I don’t want to start those debates again!

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  2. Hi Aravis,

    OK, but that’s quite a different point from the one Massimo was making. Massimo claimed that we could only have experiences if there were an external world. You are claiming that our experiences could be produced without an external world. Though the two of you proclaim that you agree with each other, to me at least it seems as if you are making completely different arguments.

    So the argument you quote was in response to Massimo’s argument, and it does indeed support your argument. My argument against you is that though the external world could be caused by a demon, it is more parsimonious to believe that it isn’t. It’s a simpler explanation and so accepting it is warranted.

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  3. You forget that Descartes’ skeptical arguments apply to reason as well as sense experience. It is a global skepticism about the reliability of *all* of our knowledge-bringing faculties. The appeal to inference to the best explanation that you are employing, here, falls right into those arguments.

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  4. Ah, well there we may be in agreement. My view on reason is that faith in reason is unwarranted but is absolutely necessary if we are going to have any kind of sensible conversation. So I’m with you there. It follows, I agree, that belief in the external world is unwarranted when this is taken into consideration. But since I think we are forced to accept that reason is possible as an axiom, I do not usually entertain any doubts in this regard. So though I would usually say that belief in the external world is warranted, I am quite happy to relax this in the context of skepticism of reason itself.

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  5. We likely have no disagreement then. Indeed, you may find the “common sense naturalism” approach that I have suggested quite amenable, if I understand you correctly.

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  6. “We’ll call it a draw” on credit! I do think it’s important, contra a Peter Unger, a philosopher who’s gone over to the dark side of rejecting the value of philosophy in a new book, that Hume never said we should pretend something like the problem of induction doesn’t exist, only that, in cases where it seemingly makes no difference in our daily lives, to act as if it doesn’t.

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  7. Here’s one take on the BIV issue connecting back to radical skepticism. It isn’t so much a refutation of the BIV argument as a meta-argument about the epistemic value of the BIV scenario.

    The short version of this can be seen (if I read it correctly) in Putnam’s paper on values in science. Let’s assume that the skeptics are correct, that we really cannot know whether or not we are brains in vats. If so, then that proposition does nothing for us. Whether we assume its truth or not changes nothing about our understanding of the (real or illusory) world that we experience. Thus, even if it is true, it doesn’t matter. (That is not to say that the BIV scenario as a topic of philosophy doesn’t matter, since the very dialogue it has generated proves that it does matter if you value philosophical discourse).

    The longer version of this starts with an answer (based on Mark Bickhard’s writings) to the radical skeptical argument, the argument that since we cannot go outside ourselves to check the accuracy of our representations, then we cannot know how true they are to what they represent, and thus, we are in the dark about whether we know anything at all. Now, if we restate the argument in terms of theory, it looks like this: we cannot go outside ourselves to check the accuracy of our theories, and thus we cannot know how true they are to what they represent. This should seem strange to anyone involved in science, since even though we cannot go outside ourselves, we do something that looks a lot like “checking the accuracy” of our theories all the time. That’s what empirical science is. Clearly, the argument was meant to address representation at a finer level than theory, but I think that by using empirical science as an example, we can get some insight into the original argument’s error.

    Theories are valuable because they reorganize our assumptions about the world in a way that allows us to make predictions regarding the consequences of our actions. If I build a giant space telescope and point it in the direction of X, then I will be able to observe Y. If I do A to one group and do B to another group, I should find D difference in measure M. Etc. And even if I feel uncertain about the theory, I do know when my predictions turn out to be correct or not. I also know when I have constructed a theory that succeeds or not in generating successful predictions, and how it compares to other theories in the same regard. Clearly, it is possible to generate epistemically interesting knowledge when we consider it from this pragmatic perspective. But notice that even though theories are about the environment, they don’t get their epistemic content from being in correspondence with the environment (if so, then we’re back to the radical sceptical problem). Instead, they get their content from what they imply about our interactions with the environment. The same argument can be made about representation at the level of individual epistemology (in fact, it has, by Bickhard).

    Now, to deal with the BIV issue. Suppose I take the BIV scenario to be a theoretical assumption. The strongest BIV theory would be that I am a brain in a vat being fed a simulation so perfect that nothing I do within that simulation has consequences different than if it were not a simulation at all. In other words, as the skeptics say, I cannot know if I am a brain in a vat. But notice that the theory does not allow me to generate predictions or tests of those predictions, at least not any different from a theory that doesn’t include the BIV assumption. In other words, the theory has no discernible epistemic content. Even if it is true that I am a brain in a vat, it doesn’t matter. The only BIV theory worth considering (at least for knowing about the world purposes) would be one that has the potential for predictable interactions with the environment, but such a theory (if successful) would imply that I can, at least in a pragmatic sense, know if I am a brain in a vat.

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  8. “(1) I don’t know that I’m not a BIV.
    (2) If I don’t know that I’m not a BIV, then I don’t know that I have hands.
    Therefore:
    (3) I don’t know that I have hands.”

    The above is indeed a formally valid argument, but it is a ‘particular’ case without a ‘universal value’. I will examine this issue with the following steps (questions).

    Question one: Is there ‘someone’ besides the ‘I’ around?

    Question two: Can he know that ‘I am not a BIV’?

    Question three: If he cannot, then why? Is he also a BIV?

    Question four: Is ‘BIV’ positively defined, that is, identifiable? If not, then there is no issue of being a BIV or not. If yes,

    Question five: Why is another BIV unable to identify a BIV when he encounters one? If the answer is ‘by definition’, then it goes to next question.

    Question six: Is there ‘someone’ besides the ‘I’ who is not a BIV around? If this question is unanswerable, then being a BIV or not is no longer an issue. If there is a non-BIV around, then goes to the next question.

    Question seven: Is this non-BIV able to identify a BIV when he encounters one? At this point, this BIV problem is no longer a logic issue but is a ‘technology’ issue if BIV is clearly defined and identifiable.

    Even while we change ‘I’ to ‘we’ in this BIV story, the problem is still on the issue of “why the he-BIV is unable to identify whether ‘I am a BIV or not’.”

    When there is an ‘external’ point outside of a system, all paradoxes in that system can be resolved from this ‘external’ point of view, and this is one important theorem of “Martian Language Thesis — Any human language can always establish a communication with the Martian or Martian-like languages” (that is, all mysteries are connected to the ‘known’ part of this universe).

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  9. While this seems to be reflected in some of the points, it does seem the introspective talent which would lead us to question the basic biological and physical basis for our existence is far shallower then the complex set of factors on which it rests. First we do have to assume consciousness, or we wouldn’t be here, asking this question, ie. “Cogito, ergo sum.”
    Then to assume this sense of being and self would either be the product of some deeper sense of being and thus in a position to be deceived by it, or is essentially being self deceptive, would go to the nature and processes of consciousness, rather than what aspects of our physical reality are “unreal.” Which is a subject for physics.

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  10. Hi Massimo,

    But we can deny these premises on grounds of implausibility, just like we would deny, say, the claim that someone has traveled through time via a wormhole on the ground that we don’t have sufficient reasons to entertain the notions that time travel is possible and that someone has been able to implement it technologically. Yes, the skeptics can deny the analogy, but the burden of proof seems to have shifted to the skeptic, who needs to explain why this is indeed a disanalogy.

    Which would be pretty easy for them to do since the skeptic is clearly not making a claim that you are a BIV. The skeptic is making a claim that you don’t know that you are not a BIV.

    So the statement “A is true” is obviously not analogous to “You don’t know that B is false”.

    It seems to me that putting the burden of evidence onto the person who claims that we have no evidence is a disastrously failing strategy.

    If you say to the skeptic “can you show that the scenario is plausible?” the skeptic can cheerfully reply “Absolutely not!”.

    Unless you are going to say that lack of evidence of plausibility is evidence of implausibility, the skeptic has now won.

    By shifting the burden of evidence you have implicitly agreed that you have no evidence. And the skeptic can say “My lack of evidence as to its implausibility means it may be highly implausible or very plausible indeed – neither of us can know which”.

    So we are left without the ability to say whether it is even an unlikely scenario.

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  11. My primal response to the BIV question, or any assertion of reality being an illusion, is to acknowledge that I can’t prove that I’m not a BIV or similar construct. I think every argument to a determined skeptic fails. However if I am a BIV, and my entire world is a simulation, then that simulation provides unpleasant consequences if I fail to take it seriously.

    So, my responses and strategies are the same whether I am dealing with a real world, where I do have hands, or a simulated reality where those hands are virtual constructs. If I put one of those hands in a fire, the consequences will be unpleasant regardless of whether it is a real fire or a simulated one.

    If I am a BIV, of if you are, we have little choice but to play the game.

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  12. HI Massimo,

    …and the low-standards version is interesting but unsound (because we would have to admit to the bizarre situation of not having even fallible knowledge of our hands!).

    In this particular case all the skeptic has to admit to is that there are some things about which we do not even have fallible knowledge.

    Did Eratosthenes have fallible knowledge about quasars? Did Archimedes have fallible knowledge about quantum physics?

    It stands to reason then that we cannot rule out that there are some things about which we don’t even have fallible knowledge.

    Since the subject matter is the set of things we don’t know then there are surely many members of that set about which we don’t even have fallible knowledge.

    Since we cannot claim to know anything about the possible scenarios in which a BIV might arise then we don’t even have fallible knowledge that we are not a BIV. For example we don’t know whether or not there are infinitely many universes and the vat can be a future time in which BIV’s are a commonplace research tool or hobby. They may have programmed the reality simulation to be set in a time before BIV’s were the case so that the BIV would not take seriously the notion that it was a BIV.

    There must be many other scenarios that I or you can’t think of and no way of deriving even an approximate probability of their being the case.

    And that is, of course, only one set of scenarios. We could have mass produced (3D printed maybe) bionic brains in some future space. Or brain simulators of some kind – unless we know that brain simulators are impossible we cannot rule any of that out.

    I might also mention that Descartes was not interested in the likelihood or otherwise of being deceived, only to be able to find some solid place upon which to base reasoning. He thought that if something was even in principle deniable then it could not provide that solid foundation. He believed that Cogito Ergo Sum was that solid foundation (although the 18th century physicist Georg Lichtenberg pointed out that the “I” was defined circularly and at most we could claim to know “there is some thinking happening”)

    But if we admit to never having infallible knowledge then we are really all skeptics.

    After that it is only a matter of how much it bothers you.

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  13. Hi Massimo! Do you know of any formal argument (perhaps a paper by you or someone else) on how Hume’s argument leads to Sagan’s more well known maxim “Extraordinary claims ….”?

    The two seem similar, but not quite identical to me. Would appreciate any comment that would suggest how they could be linked up rigorously.

    Thanks!

    George

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  14. Massimo,
    What is your top down vs. bottom up premise?
    Did that brain in a vat evolve from bottom up conditions into its present circumstance, or is it, as in the Matrix, an experiment by an higher order entity/intelligence?
    That is the crux of the assumption this situation has to first address.
    If it evolved from a bottom up base state, then why would an illusion, other than the one we experience, occur? In that bottom up process, there are many cycles of expansion/complexification and contraction/consolidation/melt downs and while these feedback loops create a layering process, the higher order layers are not necessarily invisible to the lower orders, it’s just that the lower orders travel smaller loops, they do experience the effects of those higher orders and the BIV theory has no effects to point to, other than claiming, sans evidence, that it is still a possibility.
    This then goes to the top down theory, that there is some higher order programing our lives. Which is in essence, a theological argument, that there are higher beings controlling our destinies. Now certainly there are many people who do believe quite strongly in this, yet the evidence is questionable.
    Now I would add that I’ve had enough weird things happen in my life to believe in some form of karma, but that would be some larger feedback loop, which I only sense and consider because of the questionable events, not in spite of having no evidence.
    Regards,
    JBM

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  15. I agree. The purely empirical answer is to say that by “hands” I am referring the these objects of my experience which clearly exist and then to add that I do not know and can never know their ultimate metaphysical nature.

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  16. Our most convincing communicable proof of the existence of other things is, not the appearance of objects, but the necessity of admitting that there are other minds besides our own. … When once we have admitted different and independent minds, the reality of external objects (external to all those minds) follows as of course. … There must be a somewhat independent of those minds, which thus acts upon them all at once, and without any choice of their own. This somewhat is what we call an external object: and whether it arise in Berkeley’s mode, or in any other, matters nothing to us here.

    Augustus De Morgan – Formal Logic, the Calculus of Inference 1847

    I couldn’t really put it better than that.

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  17. In order to have a formal argument around “extraordinary claims” you would have to first have a rigorous set of criteria around what makes a claim extraordinary or ordinary.

    It seems to me that those are a matter of subjective opinion.

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  18. Hi Coel,

    By contrast the “normal world” model is vastly more parsimonious, all you need are a couple of quantum fluctuations in the early universe and everything follows from that. The amount of information that needs to be input to specify the basic physics of this world is vastly, vastly less.

    Of course I could also posit a naturally occurring Wolfram Rule 110 which can be specified in 32 bits and then posit that it acted infinitely many times on infinitely random initial positions. That would also get us all the observable physics of this world given sufficiently many initial conditions and we could even prove that mathematically

    That is even less information than needs to be input into quantum fluctuations and it seems to me that quantum fluctuations still need to act on a vast or infinite random set of initial conditions in order to predict a universe like ours.

    If the criterion is the amount of information that has to be input then quantum fluctuations are horribly unparsimonious compared to there being a Wolfram Rule 110 that just happened to be the case.

    So should I prefer the Rule 110 explanation?

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  19. I think the value of the skeptical position is that it fosters epistemic humility: we are really not as smart as we often think we are, and in fact we don’t even have unequivocal answers to very basic questions about knowledge.

    This, I think, is the most important part of your paper and I applaud your statement. However, each of us is confident about our knowledge and I suppose we need to be confident in order to function. But every now and then something happens to profoundly shake that confidence.

    In my case it happened as follows. I was attacked by a swarm of bees, suffered a severe anaphylactic reaction, was taken to hospital unconscious and barely survived(Africa is full of aggressive African bees!). I recovered quickly, or so I thought. Not long after, I was watching a movie with my family and was disturbed by gaps in the plot. I questioned this and my family assured me there were no gaps. Aghast, I hurried off to my doctor and he told me I was suffering from petit mal(absence seizure), a condition where segments of a persons consciousness seamlessly and undetectably disappear. This, he said, was probably caused by mild brain damage brought on by shortage of oxygen to my brain during the bee attack incident.

    There were gaps in my consciousness and I was unaware of those gaps unless I closely studied something with a well defined timeline and compared this with other people’s experiences. Until I experienced this, knowledge seemed like a substantial, reliable thing. It seemed, though, I didn’t know and I had no ordinary way of knowing that I didn’t know. It was an astonishing discovery that was deeply unsettling.

    How then do we know that we know? I suggest that the practical answer is the one I discovered, from the feedback of those around us. We have a theory of other minds that is plausible to us because we are tightly linked to them through a social mesh. This is Daniel Goleman’s contention in Social Intelligence. It is the continual interaction and resonance of our minds with other minds that makes reality plausible. Whatever the reality, it feels so intimately plausible that for all practical purposes it is reality. It feels plausible because other minds reflect back to us what we know to be true in our own minds.

    A final note. I recovered fully through a program of intense, sustained running which seems to help promote brain healing. Or did I recover? How will I know? Perhaps the whole incident was nothing more than some electrical glitches in the power supply to the system supporting my brain in a vat. Did the Brain Vat technician repair the electrical connections to the system, one night, while I slept deeply? Why then did he set me off on such an intense programme of running? Are Brain Vat technicians really so conscientious about their jobs?

    No, my reality is simpler than the real reality, so I prefer it. Or are my preferences the source of my delusions?(Coel and DM nod in vigorous agreement at this point).

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  20. Robin,
    Our most convincing communicable proof of the existence of other things is, not the appearance of objects, but the necessity of admitting that there are other minds besides our own

    Well put. See also my comment below, about the bee attack.

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  21. I would say the Rule 110 is equivalent, because you’re assuming that somewhere within the infinite starting bits is a setup that encoded the laws of physics of this universe. Either way, the laws of physics exist. In fact, what you have described regarding rule 110 is basically equivalent to the MUH.

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  22. There are only senses (and sense organs), if the external world exists. Thus, appeal to those organs and their processes cannot justify the belief in the existence of the external world.

    But from a perspective in which the senses and sense organs *are* the “external” world – in which the separation is essentially arbitrary – the problem doesn’t arise. If my belief in my senses is justified, my belief in the world is automatically justified as well. At this point the problem becomes what the *nature* of the world is. And the fact that we can’t know certain things about it becomes less conundrum-like, because it’s consistent with the metaphysics of such a world (one in which the knower can’t become separate from the thing-to-be-known in order to observe/know it).

    It also has the benefit of making intuitive sense.

    We seem to get into philosophical trouble a lot when we use abstraction to separate things that aren’t separate.

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  23. This approach rests on rejecting the skeptic’s demand for universal warrant

    I’m not a philosopher – just an “interested outsider” with a BA in Philosophy – but my experience when I express views like that one is that people tend to say that it’s an absurd position because it leads to “nihilism”. I don’t really have a great response to that, beyond asking them to warrant the belief that nihilism is undesirable.

    I’ve found myself disagreeing with much of what you’ve said in the last two threads, but I definitely share your affinity for the later Wittgenstein (and the naturalistic reading of Hume as well – what I know of it, anyway). I look forward to reading your articles.

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  24. Hi Massimo,

    I don’t think you’ll find anyone who disagrees. The question is how do we know?

    Of course, and we’ve discussed that question upthread. I’m just reminding Labnut that while it may be a good heuristic to assume that Coel and I will always disagree with him, there are exceptions to the rule!

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  25. DM,

    “I would make the point that there is pretty much nothing about which we can be absolutely certain, perhaps not even that 1+1=2, so I don’t really think that infallible knowledge exists”

    You and I guy named Descartes. You are in good company.

    “”I have no hands”, on the other hand, is a story without context. On the face of it, it seems to be contradicted by the evidence before us.”

    I disagree, the hands question is exactly the same as the BIV. If you are a BIV, then you have no hands. Since you accept the BIV as a genuine problem, then the no-hands one has to enjoy the same status. Indeed, you yourself admits as much a few lines down.

    “Without an explanation of how it is that we are supposed to be handless”

    Why, do you have an explanation of how it is that we are supposed to be BIVs?

    Coel,

    “I think that BIV scenarios are best analysed by the scientific method”

    I got news for you: there is no such thing as the scientific method, this has been accepted in philosophy of science at the least since Kuhn. But I know what you mean…

    “We all have a stream of sensory data coming into us, and we construct models to explain and understand that stream of sensory data. The scientific method then tests them for explanatory power and predictive power.”

    As Aravis has explained, this approach begs the question: “we have sensory data” assumes that we have senses, and therefore we are not a BIV. You can’t then turn around and use that assumption to show that we are not BIVs. It’s a no starter.

    “The BIV model has little explanatory power. You have to postulate a heck of a lot (both the vat and the brain) with no explanation at all about why they got there.”

    You might have noticed that this is the fifth response to the skeptic position already outlined in my essay. And it’s not a scientific response.

    “As for predictive power (by which I mean predicting future aspects of the sensory data stream), the BIV has zero.”

    It’s got just about the predictive power of string theory…

    imzasirf,

    “the detractors of philosophy (and I’m thinking the scientists among that crowd) will say “Who cares?””

    Let them. I’m beginning to be inclined to respond who gives a crap about what you care about?

    “it’s not at all relevant to what we are doing on a day to day basis”

    Yeah, unlike speculations about the multiverse, which are surely going to end poverty and world hunger, any day now…

    Socratic,

    “I would postulate a sixth, even more psychological response: The “act as if response.””

    Indeed, but the beauty of Hume’s philosophy is that he appreciated the skeptic point, admitted to what I call epistemic humility, and only then went on with his daily business.

    “Even granted the philosophical validity of “conceptual spaces,” in something like a simple, classical formal argument, IMO, such spaces should be grounded in philosophy, not science”

    Here I’m going to push back a little. In my forthcoming book for Chicago Press I place philosophy between science on the one hand and logic/math on the other, closer to the latter. But unlike the case of math/logic, where the conceptual space is indeed entirely independent from empirical anchors, in philosophy we tend to be interested in things that pertain to the world as it is, so empirical anchors are necessary, and sometimes determine which of a number of possibilities in conceptual space make more sense. That’s a far cry from saying that “science” answered the question, pace Coel.

    Adrian,

    “Thus, even if it is true, it doesn’t matter.”

    Right, but irrelevant, as you yourself point out. Sure, if by “matter” we mean does it lead to actionable knowledge, not, it doesn’t matter. But, again, neither do string theory and multiverse scenarios, to keep beating a deliciously dead horse.

    “we cannot go outside ourselves to check the accuracy of our theories, and thus we cannot know how true they are to what they represent. This should seem strange to anyone involved in science, since even though we cannot go outside ourselves, we do something that looks a lot like “checking the accuracy” of our theories all the time”

    That, seems to me, would lead straight to a type of pragmatic anti-realism about scientific theories, which is a perfectly reasonable position to hold (though not one that I endorse).

    “Suppose I take the BIV scenario to be a theoretical assumption.”

    I think that would be a mistake, the same that Coel makes. The BIV scenario is not meant as a theory of the world, it is an argument against knowledge of the world. If you will, it is about epistemology, not metaphysics (or physics).

    “The only BIV theory worth considering (at least for knowing about the world purposes) would be one that has the potential for predictable interactions with the environment”

    Again, only if you think of the BIV as a theory about the world. It isn’t.

    tienzengong,

    “The above is indeed a formally valid argument, but it is a ‘particular’ case without a ‘universal value’.”

    I disagree, the BIV argument is general, indeed it is just about the most general argument you can make about skepticism.

    brodix,

    “the nature and processes of consciousness, rather than what aspects of our physical reality are “unreal.” Which is a subject for physics.”

    As I argued above, this has nothing to do with either physics or biology. The point is exquisitely epistemological.

    Robin,

    “he statement “A is true” is obviously not analogous to “You don’t know that B is false”.”

    Right, but the counterargument in question moves from knowing or not knowing (yes/no) to a plausibility of knowledge, i.e., it treats belief as matters of degree.

    “Unless you are going to say that lack of evidence of plausibility is evidence of implausibility”

    I believe that’s exactly what the argument is saying. In a Bayesian context, if plausibility of a belief is measured as a prior, which ranges from 0 to 1, then the closer the prior for implausibility is to 0 the closer the prior for plausibility is to 1.

    “In this particular case all the skeptic has to admit to is that there are some things about which we do not even have fallible knowledge.”

    Yes, but the point is that few skeptics will go that far. In general, the skeptic argument loses grounds as soon as we move from absolute to fallible knowledge, though it still has bite.

    “Did Eratosthenes have fallible knowledge about quasars? Did Archimedes have fallible knowledge about quantum physics?”

    That’s a strange question, they had no knowledge at all of those things. I don’t see what follows from that, in this context.

    “It stands to reason then that we cannot rule out that there are some things about which we don’t even have fallible knowledge.”

    But hands don’t follow into the same category as quasars and quantum physics.

    “Descartes was not interested in the likelihood or otherwise of being deceived, only to be able to find some solid place upon which to base reasoning.”

    I know, and that was the last glorious — and failed — attempt along those lines in the history of philosophy.

    “In order to have a formal argument around “extraordinary claims” you would have to first have a rigorous set of criteria around what makes a claim extraordinary or ordinary.”

    You can, invoking the concept of priors in Bayesian analysis.

    SelfAware,

    “My primal response to the BIV question, or any assertion of reality being an illusion, is to acknowledge that I can’t prove that I’m not a BIV or similar construct.”

    Yup, that’s the correct reaction, I think.

    “However if I am a BIV, and my entire world is a simulation, then that simulation provides unpleasant consequences if I fail to take it seriously.”

    Right again.

    George,

    “Do you know of any formal argument (perhaps a paper by you or someone else) on how Hume’s argument leads to Sagan’s more well known maxim “Extraordinary claims ….”?”

    Check out these two papers, which you can find with a Google search:

    Hume Versus Price on Miracles and Prior Probabilities: Testimony and the Bayesian Calculation, by David Owen, The Philosophical Quarterly, Vol. 37, No. 147 (Apr., 1987), pp. 187-202.

    On the Evidence of Testimony for Miracles: A Bayesian Interpretation of David Hume’s Analysis, by Jordan Howard Sobel, The Philosophical Quarterly, Vol. 37, No. 147 (Apr., 1987), pp. 166-186.

    But these are about Bayesian readings of Hume, not specifically about Sagan’s phrase. The latter was simply a metaphorical take on it, and you are right, it is not exactly equivalent to Hume, though I suspect Sagan’s could be shown to be a special case of Hume’s on Bayesian grounds.

    brodix,

    “What is your top down vs. bottom up premise? Did that brain in a vat evolve from bottom up conditions into its present circumstance, or is it, as in the Matrix, an experiment by an higher order entity/intelligence?”

    That question is entirely beside the point, since the BIV argument is not meant to be a theory of reality, as explained above.

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  26. Hi Massimo,

    Since you accept the BIV as a genuine problem, then the no-hands one has to enjoy the same status. Indeed, you yourself admits as much a few lines down.

    I think my point has eluded you. “I have no hands because I am a BIV” is a little self-contained story. Not everything is explained, such as who or what put my brain in a vat, but we at least understand how it is that we are supposed to have no hands. There are other explanations, such as “I have no hands because they were amputated a second ago and I haven’t noticed yet”, or “I have no hands because my body belongs not to me but to God”.

    “I have no hands” on its own is too ambiguous. It is prima facie false, so we need an explanation of how it is that it is supposed to be true. “I have no hands because I am a BIV” supplies that explanation, which I think changes the threshold of justification.

    This is not unlike my change in attitude to Aravis. I don’t accept that belief in the external world is unjustified when asserted without clarification, but I do accept that belief in the external world is unjustified when it is clarified that this is because faith in reason is unwarranted (and by the same token all beliefs would be unjustified).

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  27. If I can just extend this a little bit…

    Without context, if I asked you “Did you know that Pluto is no longer classified as a planet?” you would probably answer in the affirmative, and I think this would be reasonable.

    If I said “Aha, but you’re wrong! You know such thing. You could be a BIV, and therefore there would be no such object as Pluto and nobody to classify it one way or the other”, you would probably regard this as an annoying and unhelpful move.

    But if I asked you “Do you really know that Pluto is no longer classified as a planet, given that you may be a BIV”, you might have a different initial response, and I think this would also be reasonable.

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  28. Massimo, thanks for the references.

    I suspect that it might be difficult to get to Sagan’s maxim because of the word “extraordinary.” What does it mean in a more formal context? Near as I can tell, the word simply means a rather large deviation from our current theory (or perhaps our common sense about things). And there seem to be lots of scientific theories that might arguably be “extraordinary,” such as AI becoming conscious or Everett’s theory of a multiverse. Near as I can tell, no one demands extraordinary evidence for such (and other) extraordinary arguments. Good, strong evidence will do. (Of course whether such evidence can even in principal be found for Everett’s theory is another question.)

    So, it seems as if Sagan’s maxim is not really applied, at least in an uneven way, across science. And that’s probably because different people have different ideas about what “extraordinary” means.

    Thanks again!

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  29. In my comment above, I showed that the issue of ‘am I not a BIV?’ is answerable if there is a ‘he’-agent (not of the ‘I’) around regardless of whether this ‘he’ is a BIV or not.

    In the Chapter 3 of the book “The Divine Constitution, ISBN 9780916713065”, it discussed a ‘paradox axiom’ {No Mystery Thesis (NMT)}:
    One: for any mystery {paradox (logic) or physical (dark matter, dark energy), etc.}, it is always resolvable if there is an ‘external’ point outside of that mystery-space.

    Two: for any mystery-space, there is always an external-point outside of it.

    This NMT is supported with three points.
    First, with mathematics (the Godel incompleteness theorems): if this mystery-space is a (any) formal system (however it is constructed), there is always a ‘point’ outside of that mystery-space.

    Second, with physics equation: the ‘now’ is the ‘external-point’ of the entire history of this universe, and this is described with the ‘Space-time force’ equation.
    F (space-time force) = K ħ/ (delta S x delta T)
    This equation gives rise to ‘uncertainty principle’ and ‘gravity force’, and these two describe the entire history of this universe. The details of this equation is available in the book “Super Unified Theory; ISBN 9780916713010”. A brief description of it is available at http://prebabel.blogspot.com/2013/11/why-does-dark-energy-make-universe.html .

    Third, with the “Martian Language Thesis (MLT) — Any human language can always establish a communication with the Martian or Martian-like languages”. MLT is based on the solid fact that both human and Martian share the followings:

    One, the same meta-space (encompasses the same physics laws, the same history of this universe, etc.)

    Two, the same ‘meaning-space’ {the meaning of every ‘object’ and ‘event’ of this universe (having an intrinsic existential meaning (IEM) and radiating out some additional info into the environment) is the same for both human and Martian}.

    That is, every point in the meta-space (the entire history of this universe) has a meaning-point (the external point) in the meaning-space. For a syntax without any semantics is still having a meaning-point of (zero, void or nonsense) in the meaning-space. The details of this ‘Martian Language Thesis’ is available in the book “Linguistics Manifesto, ISBN 978-3-8383-9722-1”. A brief description of it is available at http://www.chineselanguageforums.com/linguistics-f25/language-types-and-second-language-acquisition-t222.html#p1933 .

    With these three points, the “No Mystery Thesis (NMT)” is guaranteed. Thus, ‘Am I not a BIV?’ is definitely having an answer.

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  30. There is a sensory organic system and a logic one, they work together. I think that we don’t appeal the existence of the external world, what we do is to handle a theoretical model that allows the action with the external world. If the external world doesn’t exist the model is solipsist or tends to be. If the external world exists, the sensory and logic models that we build up prove the existence of the real world outside the subjectivity of the human agent, we have to build them up to deal with it.

    The experimental physics studies, predicts and theorizes about physical phenomena like gravity, electromagnetics particles, nuclear forces, etc. The gravity force that attaches objects and bodies to the ground is sensory and logic? Or sensory and logic mean that which springs out from the theoretical model? Seems that the gravity force shows that the external world exists no matter how bright would be the hypothesis that seeks to refute it. It means that the external world is real and challenges the human agent and his technology.

    These phenomena are measured by different devices, this is one way of perceiving the existence of the material world. We know about the external world with the help of technology, then there is a coincidence between the sensory and logic systems and the technology handled by the experimentalists. I think that the external world is real and also that our models that describe natural phenomena are provisional and still have scope to improve.

    In my opinion, the Pyrronic skepticism doesn’t tell us that the outer world doesn’t exist, what says is that is possible to stop our judgments about the external world. The question that arises is ¿to stop the judgments about the external world modifies it? The Pyrronic discourse owns some peculiarities that seem to encourage the suspension of judgments, and therefore there is little room for philosophical speculation. The theoretical speculation is based on a flow of mental processes, ideas and feelings that are subjected to review and critique. Thus, the epoke or suspension of judgments advocated by Pyrrho seems to sneak up the usual analysis based in chains of inferences, judgments, statements, dialectic and emotional maneuvers to picture reality. If there are not judgments, what sort of conceptual space arises? It makes little sense to talk, speculate and theorize if there is an agent stripped of judgments.

    Seems that the Pyrronic skepticism has an orientalizing bias which places it near the Buddhism, that’s why few modern philosophers are interested in Pyrrhonism.

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  31. Massimo,
    “As I argued above, this has nothing to do with either physics or biology. The point is exquisitely epistemological.”
    Don’t we intellectually generate reams of speculative positions and then have to sort the wheat from the chaff?
    Yes, we could be BIV, but then fairies and unicorns could be living in the woods behind my house. The situation is that we do have to sort through and decide which are viable considerations and which are not. Among the various tools to do this are evidence and pattern recognition. Is there evidence to support it and does it fit within a broader pattern.
    Like religions shows, often this can be a difficult process and there are many dead ends. The more effective solutions tend to be those with the most evidence to support them and have the broadest applications.

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  32. My vote is for a slap across the cheek as a way to demonstrate, empirically, the existence of my hands. Nothing ‘conceptual’ about it. … so to speak. I probably just don’t get it, but firstly, I have problem with the idea of a concept continuum. I’d say its more of a topological space (with the implied potential absence of a metric (“higher” , “lower”) across all subspaces.) Secondly, my first reaction to this is that y’all are being very, very sloppy in your concept of the “I”. Its clear to me that any definition of a physical I could, without much difficulty, be empirically verifiable. (If my hands are amputated, are they no longer mine?, etc.) If the argument is intended to be concerned with with some sort of concept of abstract existence, then we’re back to the uncountable choices of the abstract topological spaces, imho. I guess my major problem with this argument, as well as several of your others I’ve read this week (newly discovered this blog), is your apparent assumption that there exists something called “truth” – in the absolute sense you use it. I know I have hands. Seems to me so simple that a discussion on it is mostly flatulence. Can one structure the definitions (including contexts (to an acceptable degree)) so that the truth value is “TRUE”? Yes. Can one structure the definitions so that the truth value is “FALSE”? Yes. Can one structure it so that the truth value is “Indeterminant”? Yes. Leaving me wondering what I must be missing here. Seems like studying navel lint would be time better spent. No offense. BIV is a concept of which you admit has no physical reality. Given that, it should be (again, am I just really really off base here?) obvious that without an exhaustive definition of such a pseudo-concept (“pseudo” meaning that the words do not map to anything empirically verifiable), using it (to communicate with others not sharing the same abstract set of model characteristics) is virtually certain to be useless. I guess (top of my head) that this reduces to the “Describing red to a blind man” problem. BIV is to existence as Red* is to a blind man. (*visually speaking) Oh, also – I’m not totally on board with the claim that philosophy is about concepts, its about communicating and analyzing concepts. Seems to me anyone with a blog will know this. Utility and empirical verification. which does the argument given here contribute towards? I just don’t see it, said the blind man.

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  33. DM,
    My view on reason is that faith in reason is unwarranted but is absolutely necessary if we are going to have any kind of sensible conversation. So I’m with you there. It follows, I agree, that belief in the external world is unwarranted when this is taken into consideration.

    Massimo in asked “The question is how do we know?

    Informed philosophers will tell you we don’t know. But we act as though we know that BIV is not true and the vast majority of people really do believe that BIV is not true. In fact it not just a belief, it is a certainty in their minds.

    The truth/falsity of the BIV hypothesis is interesting for the reasons that Massimo mentioned but, for me at least, the really interesting question is why do the vast majority have the certainty that the BIV is not true?

    We never arrived at that conclusion by careful argument. It is a powerful intuitive assumption built into the fabric of our lives. It is so powerful that even trained philosophers, when examining the BIV argument, still have no doubt that the BIV is false.

    What accounts for this simple, powerful and intuitive certainty?

    Robin argued
    the necessity of admitting that there are other minds besides our own. … When once we have admitted different and independent minds, the reality of external objects (external to all those minds) follows as of course
    and I agreed with him, referring to Daniel Goleman’s idea of a social mesh.

    You earlier appealed to parsimony, saying that this requires the simplest explanation. Unfortunately there is no reason why reality has to be parsimonious at the level of your perception and that rather puts paid to that argument.

    But I agree with you in another sense. Our brains would seem to apprehend reality by constructing simplified internal representations. If that is the case then the limited capacity of our brains would tend to make us prefer simpler explanations and so the need for parsimony would seem intuitive and natural, because our brains need simpler models.

    I think then that we have this simple, powerful and intuitive certainty that the BIV is false, for a combination of reasons:
    1) as we mature we construct working models of the world that appear consistent and coherent,
    2) we experience causal agency,
    3) we powerfully experience qualia,
    4) we perceive other minds and they reflect our perceptions of the world, giving us validation,
    5) it is a parsimonious explanation and we need parsimony.

    None of these things, separately, or taken together disprove the BIV hypothesis but they are sufficient to create the powerful illusion that the BIV is false. Hence no one seriously entertains the BIV hypothesis.

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  34. Upon reflection, I like the “knowledge-that” approach. In some ways it’s a “wishful thinking” approach because it’s like saying, “this answer is preferable because it gives us a world we have the ability to understand”.

    But on the other hand, it works because it brings out the imbalance between BIV=true and BIV=false in terms of explanation. You can say “BIV=false and this is how it works”, but you can’t say the same for BIV=true.

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  35. Hi Labnut,

    I don’t usually equate knowledge with certainty. When I say I know, I mean that I have justified confidence.

    As explained, I usually assume that I can reason approximately reliably as a necessary precondition of engaging in any kind of thought or discourse, though I admit that I cannot justify this. But taking this as an axiom, other beliefs are justifiable.

    My belief in the external world is justified by parsimony. Parsimonious explanations are not required to be correct, but they usually are and so parsimony is enough to warrant confidence.

    As for your criteria:

    (1), (2), (3) and (4) are in my view consistent with being a brain in a vat, and I don’t see why you think they wouldn’t be. I of course agree with (5).

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  36. A number of people, here, seem to me to fundamentally misunderstand the value of engaging the skeptical arguments.

    The skeptic is not some person who stands in your way and will not allow you to move forward, unless you defeat him. So, all this effort to prove that I’m really not a brain-in-a-vat or that I’m not really dreaming, is really quite wasted. As are all the “gotcha!” arguments and “a slap across the cheek will prove there are hands” (the latter of which, misses the point, twice — once, because it misunderstands the skeptic’s challenge, and twice, because it misses the point that tactile sensation is as much subject to the skeptical arguments as vision or hearing),

    The value of engaging the skeptic is to better understand our own conception of justification. On what grounds *do* we believe the things we do and why? How strong are they really? And–most importantly–what, if any, limits are there, to our capacity to provide sound reasons for our beliefs? Rather than some annoying, irrelevant opponent, then, skepticism becomes an indispensable tool, not just in our search for knowledge, but self-understanding as well.

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  37. tienzengong: “The above is indeed a formally valid argument, but it is a ‘particular’ case without a ‘universal value’.”

    Massimo: “I disagree, the BIV argument is general, indeed it is just about the most general argument you can make about skepticism.”

    Agree with you 100%. I did not make my point clear at that point.

    My view was that ‘the BIV argument’ (as it was presented) is in a totally isolated box, and there is no such a box in the real world. Even the black-hole is not a totally isolated box as it still interacts with the outside world via gravitation. That is, that BIV box must be tailor-made, and thus became ‘particular’.

    Thus, I made comments with two steps.
    One, BIV issue is solvable if there is a ‘he’-agent outside of that box.
    Two, to show that no ‘totally isolated box’ can be found in this universe.

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  38. DM,
    we need not quibble about the difference between justified knowledge and certainty since I was talking about the beliefs of the average person. My question was
    why do the vast majority have the certainty that the BIV is not true?
    so you see I was not talking about you.

    (1), (2), (3) and (4) are in my view consistent with being a brain in a vat, and I don’t see why you think they wouldn’t be. I of course agree with (5).

    I think you have misunderstood my words(may I say that?).
    I said
    None of these things, separately, or taken together disprove the BIV hypothesis
    in other words I am saying they are consistent with a brain in a vat (BIV hypotheis).

    Just to clarify. A sufficiently good BIV simulation would, by definition, be undetectable by the subject. Whether it ever could be feasible to construct such a simulation is another discussion. We are assuming it is feasible.

    Massimo had, I think, three purposes in mind,
    1) to illustrate the need for epistemic humility in skepticism. Very few people picked up on this. Maybe skeptics don’t like to be told this? Maybe critical thinking is a handy tool reserved for their disbeliefs?
    2) to illustrate the power of philosophy to explore and clarify conceptual space. He succeeded admirably in this.
    3) to promote discussion of the five viewpoints and thus illustrate the difficulties of arriving at a clear cut choice. This is where most of the discussion was and it proved Massimo’s point.

    To this I added a fourth consideration by asking the question: why do the vast majority of ordinary people, as well as philosophers have this certainty that the BIV hypothesis is false? I tried to provide an answer and I hope others will add to this.

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  39. Michael,
    that is an interesting distinction and you have provoked me into expanding your definition:
    1) the combative skeptic, has a point to prove, applies critical thinking to his disbeliefs(an ideologue).
    2) the honest skeptic, applies critical thinking to all his beliefs(an agnostic).
    3) the curious skeptic, asks why people hold those beliefs(an inquirer). His main concern is not to destroy beliefs but to understand their nature, their origin and the reasons for their hold on people.

    Sadly, combative skeptics, the ideologues, dominate the field.

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  40. Hi Massimo

    I wrote:

    “Unless you are going to say that lack of evidence of plausibility is evidence of implausibility”

    You replied:

    I believe that’s exactly what the argument is saying. In a Bayesian context, if plausibility of a belief is measured as a prior, which ranges from 0 to 1, then the closer the prior for implausibility is to 0 the closer the prior for plausibility is to 1.

    But absence of evidence does not affect a Bayesian analysis. Absence of evidence of plausibility is also absence of evidence of implausibility.

    In the absence of any evidence the prior for implausibility and plausibility are equal.

    But hands don’t follow into the same category as quasars and quantum physics.

    I never said they were.

    Quasars to Eratosthenes and quantum physics to Archimedes were in the category of things that they had no knowledge of, not even infallible knowledge.

    If I was a BIV then the scenario or circumstance in which I came to be a BIV would be in the same category.

    So I can’t say I have fallible knowledge that I am not a BIV because there are BIV scenarios which fall into the same category as quasars to Eratosthenes and quantum physics to Archimedes – things about which I don’t even have fallible knowledge.

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  41. That seems pretty accurate to me :). I strive to be #3 but probably fail too often.

    I think in philosophical issues like this, the combative skeptics (or the people who say it’s not worth thinking about) are missing out. It’s wonderful and strange to think that we live in a reality that prevents us knowing about it.

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