Is the “external world” real?

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Murali

Murali did his undergraduate degree in molecular biology with a minor in biophysics from the National University of Singapore (NUS). He then changed direction and did his Masters in Philosophy also at NUS. Now, he is currently pursuing a PhD in Philosophy at the University of Warwick.

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  1. Avatar Michael Drew
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    I think I basically agree. We don’t really know what the world is really “like.” In a sense it’s impossible because anything that the world is “like” is a perception, not a property of the world. the world is a radically different thing from any perceptions of it, and questions about what it is like disappear in the absence of a perceiver creating perceptions of it. BUt those perceptions are very different things from much of the rest of the world.

    IANAP, but this is how it looks to me. Cut a brain open. Is what you find there like a tree? Not at all. The probability that the world is like our perceptions of it seems to me to run close to 0/1. A tree is presumably like something (maybe it’s rough and round and vertical!), and is presumably real (if it’s real), but it isn’t anything like a human’s see-touch-smell experience of it, which occurs inside her brain and is warm, wet, and waxy.

    For me, then, the question really is, what are the criteria we have in mind for for “realness,” whether as applied to a tree or the external world more broadly? If the external world consists of a Demon’s vast warehouses of brains in vats, or if we are a computer “simulation,” – if that really turned out to be how the world is – those are still “real” external worlds, are they not? So it seems to me that when we consider realness, what we mean is whether the outside world “really is like” our perceptions of it to enough of a degree to be able to say that it’s “real” in that way. Except, again, our perceptions are real things in the world. They are parts of our brains. I feel comfortable in saying that, no, the external world is not very much like the parts of my brain where I perceive many parts of it, except in those places where the external world is no longer external to my perceptions and is instead identical to them, i.e. in those parts of my brain where they occur.

    I guess what I’m saying is that I think this problem is misconceived in important ways. Yes, the outside world is real in the sense that it has a physical reality, but it isn’t at all like our perceptions of it, which are things in the world very unlike much of the rest of it. That just seems clear to me. There are ways the world could be that we could probably argue correspond better to our perceptions than others. But I maintain the correspondence will still turn out to be really quite attenuated when you really look at it. Meanwhile there are lots of ways the world could be that would be not that much more unlike our perceptions of it than in my opinion a tree is to a human’s perception of a tree that, as it happens would conform to exactly what our ideas of what a quintessential “not-real” external world would be like. By which I mean, brain-in-a-vat scenarios. I don’t think the world consists of brains in vats (expect to the extent that it obviously does in important ways), but I actually don’t think that the ways that brain-in-vat scenarios diverge from what our perceptions of the world are is actually so importantly different for the purpose of this discussion from the way that I think the world as it actually is diverges from our perceptions of it. The world is in fact not like our perceptions of it (cut open a brain and see!). To the extent that by, “Is the external world real?” we really mean, “Is the world like our perceptions of it?,” and I think that’s to a quite great extent, then in my view there is good evidence to think the probability that it is is close to zero. Just cut open a brain and compare what you find to tree.

    So I guess I am a deep skeptic of “external world realism” as I understand what I think we really mean by it. The “external world” is wild and wacky and very much not like we experience it. I don’t think it’s nearly as loopy or controversial to say that as it might seem when we stop and think for a moment about what we really are trying to say when we try to say that the external world is “real.” If it were brains in vats, it would still be a real external world, and yet that is the scenario we contrast to that description. Whatever the brute, unperceived world really is, in my view the probabilities are that the overwhelming majority of it is hugely unlike the perceptions of it that perceivers experience – even the parts the perceivers perceive themselves to be directly perceiving. The exceptions literally are the perceptions, which are exactly like themselves.Report

  2. Avatar PPNL
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    I really think everyone is over thinking this. Any universe where induction isn’t useful is a universe that cannot support intelligent life. Without detectable pattern there can be no learning or planning for the future. There can be no mechanism at all since any mechanism depends on repeatability. Without mechanism there cannot even be life.

    A caveman can observe that the sun rises in the east and sets in the west. He has no idea why or if it will always be that way. He does not need to in order for it to be useful. It is repeatable and dependable on a time scale relevant to his life. Induction isn’t a logical principle at all. It is only pattern recognition. That’s why even unreasoning creatures can use it.

    Is the world real? I don’t even know what real means. All I know is that the utility of induction is a prerequisite for my existence. Even if I am a brain in a jar induction still works.Report

    • Avatar Stillwater in reply to PPNL
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      Is the world real? I don’t even know what real means.

      I’m throwing this comment in here, since I think this is an interesting question to ask tho what follows isn’t meant to be a criticism of anything you (PPNL) have said.

      I think there’s two ways the brain in a vat can be used against realism. The first is as some sort of reduction of sensory evidence suggestive of an external world to subjective phenomenological properties. It’s not a straight reduction, it seems to me, but it leads to things like Berkely’s Idealism and the like where the only things we can know (as in justified true belief) is a Cartesian “I am” sort of thing. Or, in the empiricist’s language, a Humean perception sorta thing, where the only thing that’s real are sense data, or somesuch.

      THe other way brains in a vat are used against realism of the external world, it seems to me, is to focus attention on the methods of justification for the belief that the external world exists and demonstrate that such a belief isn’t necessary. (That is, cannot be proven via any valid argument consistent with the evidence upon which the belief could possibly be justified.)

      In either case, it seems to me that brain in a vat argument fail to establish, let alone support, the idea that either god exists or that our belief in the external world rests on faith. Those arguments fail to support god because if the entirety of our epistemic experiences are consistent with being a brain in a vat, then we are not justified in holding any beliefs beyond the sensory inputs which comprise the phenomenological properties experienced by a vat-bound brain. ANd it fails to establish that our belief in the external world rests on faith since, by hypothesis, for a brain in a vat there is no external world (at least, not one that the brain interacts with an independent agent), yet the experiencing brain will continue to act as tho an external world exists (that is, the experiencing subject will continue to be rationally justified in acting as tho his or her actions entail predictable consequences following perceived regularities).Report

      • Avatar Murali in reply to Stillwater
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        @stillwater

        In either case, it seems to me that brain in a vat argument fail to establish, let alone support, the idea that either god exists or that our belief in the external world rests on faith

        I’m currently not interested in establishing whether God exists or not.

        ANd it fails to establish that our belief in the external world rests on faith since, by hypothesis, for a brain in a vat there is no external world (at least, not one that the brain interacts with an independent agent), yet the experiencing brain will continue to act as tho an external world exists (that is, the experiencing subject will continue to be rationally justified in acting as tho his or her actions entail predictable consequences following perceived regularities).

        You are conflating whether we are practically rational in acting as if we believed that the world we experienced was real with whether we are epistemically rational in believing it to be the case. The former can obtain without the latter being the case since, as I show above, if we our utility for phi-ing is higher than for not when the external world is real, it continues to be so even when we come to seriously doubt that the world is real. As long as we are not certain that the external world is not real (and there seems to be no reason why we should be certain that it isn’t) what practical rationality requires of us does not change. My question concerns epistemic rationality and the mere fact that a brain which is actually in a vat will likely continue to believe that it is not does not mean that it is rational to believe such.

        High levels of confidence that the world we observe is real requires faith (or at least requires us to ignore basic Bayesian calculations)Report

      • Avatar Stillwater in reply to Stillwater
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        You are conflating whether we are practically rational in acting as if we believed that the world we experienced was real with whether we are epistemically rational in believing it to be the case.

        I don’t think I am. I concede that the principle of induction cannot be established as a necessary principle by a deductive (or any a priori) argument. Hume established this a long time ago, no? I’m conceding that. So what am I conflating here?

        My question concerns epistemic rationality and the mere fact that a brain which is actually in a vat will likely continue to believe that it is not does not mean that it is rational to believe such.

        Depends on what you mean by “rational”, it seems to me. If you’re conception of rationality is that we’re only justified in acting on beliefs that result from a priori logic, or can be validly deduced from self-evident principles, then you’re right. But it’s a trivial, too. It’s also a reductio on drawing any inferences regarding the supposed entailments deriving from Brain in a Vat type thought experiments, since if we are brains in a vat, then absolutely nothing logically follows except for (maybe!) sense data and a Cartesian “I am”. Certainly we can’t draw any conclusions about faith in the external world since that faith is not only not justifiable, it’s flat out false – by hypothesis, there is no external world.

        What conclusions can be drawn from the BiaV? IT seems to me the only thing it establishes (assuming it’s a sound argument) is that there can be no proof demonstrating that the external world is necessary. Why think demonstrating that is necessary for individuals to be justified in believing that the sun will rise in the east tomorrow? I mean, arguing that the sun itself is illusory doesn’t refute the subjectively experienced regularity perceived by individuals regardless of whether they’re vat-brains or not.Report

      • Avatar Stillwater in reply to Stillwater
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        High levels of confidence that the world we observe is real requires faith (or at least requires us to ignore basic Bayesian calculations)

        See, I just don’t see how this follows. IF anything, it would require massive delusions, since if we’re brains in a vat then the thing you’re ascribing faith to (the external world) doesn’t even exist. That’s not an example of faith that something might be the case, it’s an example of a radically false belief about something that is the case. What would be the reason to conclude we’re actually brains in a vat? Certainly not merely the possibility that it’s the case. All that possibility does is establish that the external world (our conception of it, anyway) is not necessary. But from within the confines of the vat, I’m entirely justified in saying – as I just did – that the mere possibility that I’m a vat-brain doesn’t mean my belief in perceived regularities isn’t justified. All it means is that they aren’t logically necessary. But we all agree with that already. (Thanks to Hume, atually.)Report

      • Avatar Stillwater in reply to Stillwater
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        Btw, I can’t help but think that a careful reading of Kripkenstein clears up a bunch of the puzzles that appear when thinking about this stuff. I mean, the first section of the Investigations includes the line that when the shopkeeper receives the order for five red apples, his response is to merely “act” in accordance with certain types of rules he’s learned. That is, he’s justified in acting as he does even tho on a strict truth-conditional analysis his actions would be unjustified.Report

      • Avatar Murali in reply to Stillwater
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        @stillwater

        The probability calculation shows that sceptical scenarios as a whole are not just possible, they are equally consistent with the available evidence and almost as likely as non-sceptical scenarios.

        Remember, given the possible worlds model of inductive and abductive reasoning, in order to establish the likelihood of a given explanation, we examine the fraction of experience consistent possible worlds that are consistent with the explanation.

        In this case, the logical possibility of systematic deception coupled with the relative lack of complexity make such scenarios sufficiently likely to warrant serious scepticism.Report

      • Avatar Stillwater in reply to Stillwater
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        I’m just not feeling the force of that, Murali. THe mere possibility of being a BiaV is enough for the skeptical claim to go thru. THe degree to which it’s likely that I am a brain in a vat seems irrelevant at that point, at least as far as the issues we’re talking about are concerned. But you still aren’t understanding my main point here – which is probably my fault – so I’ll try it again. THe mere possibility that we’re brains in a vat doesn’t entail faith in the external world, since if the hypothesis that we’re vat brains is true then so-called faith in the external world is definitionally incorrect. And if we’re not vat-brains, then our belief in the external world is correct and not an act of faith. The two things are just completely disconnected.

        ALsotoo, my acting as I do – which includes certain justifications for my beliefs are exactly the same regardless of whether I’m a brain in a vat or not. Eg, it’s entirely possible that the laws of logic I appeal to when making sound arguments are illusory and piped into my consciousness by evil demons at a control panel hooked up to my brain, but since I cannot reasonably conclude that such a being could exist without invoking those logical laws, I must retain my belief that using them continues to be (despite the hypothesis!) justified in the deepest sense of that word. It’s just something I cannot rationally abandon without the very argument suggesting I do so reducing to absurdity.Report

      • Avatar Murali in reply to Stillwater
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        @stillwater

        I think you are misunderstanding me. If I were to claim that people who believe that the world they experience is real do so on faith, it would not necessarily be with any approval as a valid epistemic move.

        Moreover, the mere correctness of a belief does not preclude it being believed on the basis of faith. Consider the existence of God. Tim Kowal, to take an example, is a Catholic IIRC. It is logically possible that Jesus could appear tomorrow and say that Tim’s religious beliefs are more or less true. That would not change the epistemic status of Kowal’s beliefs today: namely that his religious beliefs are not justified by the relevant evidence and that faith, to some extent or another, underlies his beliefs. If a belief can be rational (well supported by the available evidence) but still wrong, then a belief can be irrational (not well supported by evidence) but still correct.Report

    • Avatar Chris in reply to PPNL
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      The anthropic principle of induction. Awesome.Report

  3. Avatar Murali
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    Any universe where induction isn’t useful is a universe that cannot support intelligent life. Without detectable pattern there can be no learning or planning for the future. There can be no mechanism at all since any mechanism depends on repeatability. Without mechanism there cannot even be life.

    How do you know this?Report

    • Avatar PPNL in reply to Murali
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      How can you make plans in a universe where every event is independent of every other event? How can such a universe support even the mechanical functions of your body?Report

      • Avatar Murali in reply to PPNL
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        Again:

        How do you know you have a body?Report

      • Avatar PPNL in reply to PPNL
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        Again:

        How do you know you have a body?

        In an absolute sense I don’t. In an absolute sense I don’t even care. Only the Sith and mathematicians deal in absolutes.

        The mistake that people make about induction is they think it is a logical principle that allows them to prove stuff. I say again it isn’t. It only detects patterns. The theories that you build from those patterns are your own. Brain in vat covers the pattern as well as anything else. Its only problem is that it contains major elements with no utility or purpose.

        If I am a brain in a vat with a computer plugged in then that is still a pattern that supports mechanism and reason. In that sense it isn’t even an argument against realism. It is only an argument that our understanding of the universe is incomplete. Well ok but we already knew that.Report

  4. Avatar zic
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    I think it was William Bell who described trying to understand subatomic particles as akin to trying to understand a bowling alley by rolling a ball across the lanes. Our brains are like that process — we get limited information, we misinterpret that information. It’s not the cognitive output of one that constitutes knowledge, it’s cumulative observation and re-observation thanks to our ability to communicate.

    Discussions like this always disturb me, the are extremely egocentric. But human knowledge does embrace that 1) humans are relatively new, 2) the earth is many millions of years older, and 3) the universe is many billions of years older, still. Reality happened before there were humans to observe, before we were rolling our balls at right-angles to the lanes. Reality does not require an observer; understanding reality does. It’s nice that we try to understand things, that we constantly work to understand things. I understand that sound is the air, vibrating. This is a physical thing. Sound is also the air vibrating my ear drums; so if I’m not there to hear it, is it sound? This is a game, though, just a word game. Even if I’m not there, the tree falling still vibrates the air. If there were not living things to observe it, I could still theoretically set up recording equipment to capture it. There is still he echos of that vibration re-vibrating the air.

    One of the most valuable lessons one learns from some recreational drug use — particularly hallucinogenics — is that human perception is very delicate and subject to distortion. Moldy grain, infested with rodents, and the hallucinogens so produced by that biochemistry, go a very long way to explaining the dark ages. This is a good thing to remember; reality is one thing, our perception of reality another. Just because I once experienced an apple tree embracing me does not mean that sometimes apple trees give people hugs.

    We get too caught up in observation as reality; things happen unobserved, and being unobserved, we may not know they happen, but they still happen. So there are two separate things here: what reality is, and how we observe reality. Conflating the two into a single thing is, to me, seems as silly as thinking I’m the pinnacle of evolution on a flat earth at the center of the universeReport

    • Avatar Murali in reply to zic
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      But human knowledge does embrace that 1) humans are relatively new, 2) the earth is many millions of years older, and 3) the universe is many billions of years older, still. Reality happened before there were humans to observe, before we were rolling our balls at right-angles to the lanes.
      @zic

      To call that knowledge, we must establish that such beliefs are at the very least justified and true. Sceptical problems reach to the heart of justification. Are our beliefs really founded on good reasons? We criticise those who justify Christianity by appealing to the Bible and in turn justify the appeal to the Bible by appealing to Christianity. Are we any better off when it comes to the “external world” or induction? Stones and glass houses and all that.Report

      • Avatar zic in reply to Murali
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        Well, I don’t believe that the bible is the ‘word of God,’ I believe it’s a collection of stories by people, and that God was created by people to explain things they did not understand and create some organizing tribal social stability.

        But the real answers to your question?

        Turtles all the way down. Or 42. Take your pick; it’s nonsense no matter how you approach it. Reality does not need you or me, we’re just along for the ride, and I’m most grateful for the opportunity. What you’re discussing is what/how we perceive what’s ‘real.’ I cannot see much of the light spectrum, hear much of the sound spectrum. But that does not mean it is not there. I can’t see electrons, but I’m sure they flow though the circuits on my computer as I type. I cannot detect photons as individual things, but there is light all about me. For all these things, we’ve devised methods of observation that consistently work under specific rules. Gravity does not fluctuate, changing the rate at which my computer crashes to the floor when it slides off my lap; but I’ve seen the video images of bubbles of water floating in the space shuttle.

        For God, for gods, the proof of their existence is only in our need for explanation and order. The gods themselves are how we fill in the blanks. Inducing god vs. deducting the human need for answers seems pretty obvious to me.

        Perhaps I’m a god. Or a universe. I’m certain the flora and fauna within me think so, if they can think with their little single-celled bodies that I cannot see without aid of a microscope. They can most certainly detect food, predators and mates. And I certainly could not live without them; and that is the really important thing to induce about godhood.Report

      • Avatar Murali in reply to Murali
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        I’m asking how do we know that the things we perceive are real? I’m not asking whether there is anything real*. If we wish to claim the mantle of rationality, then we better be willing to scrutinise all our beliefs; even the seemingly obvious ones. Otherwise, I don’t think we are in a position to criticise others for their failure of epistemic rationality.

        *Though, since, it seems that the only thing that we know for sure is real is our own selves, it may not be clear if anything apart from ourselves is real.Report

    • Avatar zic in reply to zic
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      I’m asking how do we know that the things we perceive are real?

      And that’s exactly what I’m saying is nonsensical. That we perceive it does not make it real or unreal. Go pop some LBMs and what you’ll perceive will certainly seem real until they wear off. Seriously, I think the best answer to this question is hallucinogenic experience, which is probably why it’s so important to so many rites-of-passage into adulthood.

      Two people, or even two hundred people, can all see the same rock and see ‘rock, though there will be difference in what each perceives about rock. Two people or two hundred people on LBMs will see the same rock and each see a different thing. You might see pink elephants dancing inside it, I might see roses growing through it’s stratum. Jaybird will definitely see cats. But when the LBMs wear off, we’ll all see rock again, and we’ll have a much clearer notion of the difference between real and our perception of real, and some handle on how fragile our perception can be.Report

      • Avatar zic in reply to zic
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        @murali

        I actually deal with the problems of real vs. not-real often. I get severe migraine, often optical migraine. What’s real is, sometimes, very difficult to sort out. For instance: one day, there was a car parked in front of my house, under a tree, where cars don’t normally park — that side of the street has ‘no parking’ signs on it. The sun was shining down through the leaves, and reflecting off the car. And I had migraine. For about 20 minutes, every time I looked out the window toward where the car was, my brain interpreted the light reflecting off the roof of the car as a chess board hanging in the sky. I could walk away, go back to the window, and it would still be there. The sun moved on enough that the reflection changed, and the chess board disappeared.

        Now that chess board floating in the air appeared very real to me. But I know it was a combination of light, shadow, perhaps heating air, and electrical storm in my own brain; and in fact, there was no chess board at all.

        It’s very easy to get caught up in this right up until sorting reality from brain scrambling becomes an important survival tool. And that helps one sort things out pretty quickly.Report

  5. Avatar Jaybird
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    One of my professors dealt with these types of questions thusly:

    He kicked a rock.

    No, wrong professor. He said that these questions were all well and good but, at the end of the day, you still have to feed the cat. Which isn’t exactly an “I refute it thus” but you can’t help but notice that the downsides to not feeding the cat are worse than the downsides of feeding him (and the upsides to feeding him are better than the upsides to not).

    When it comes to skepticism, there are degrees beyond which it’s downright unhealthy but, more importantly, there are degrees beyond which it is obviously playing the burden of proof game where it comes up with scenarios that it’s your job to disprove rather than the other guy’s job to establish.

    There’s a level of skepticism that is downright useful (if not healthy). It’s just not waaaay over there.

    I mean, it takes one level of skepticism to say “I can’t prove my body doesn’t exist” and another to say “I can’t prove that things happened before today” and yet another to say “I can’t prove that Abraham Lincoln existed” and then yet another to say “I can’t prove that other people dream” and up and up until you get levels of skepticism where, yeah, it’s probably not only useful but entirely fair to make the other person shoulder the burden of proof.

    But it’s somewhere after Euclid.Report

    • Avatar Murali in reply to Jaybird
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      I think my last section showed that even if you are a sceptic, you still have reason to feed your possibly unreal cat. I do think that a lot of burden of justification talk is overblown and is often a cover for people who wish to heavily scrutinise others’ beliefs without applying the same level of scrutiny towards their own.Report

      • Avatar Jaybird in reply to Murali
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        I have more reason to feed him than I have reason to believe (!) that he’s possibly unreal.

        To focus on the latter as interesting once one is out of college and/or out of weed, is to make a mistake.Report

      • Avatar Stillwater in reply to Murali
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        I have more reason to feed him than I have reason to believe (!) that he’s possibly unreal.

        Exactly. Well, sorta exactly, it seems to me. The key here is in what sense we think the cat is not real, and is there any reason to think the cat’s unreality is disanalgous to my own (as the experiencing subject) or your own (as just another cat-like object in my world)? Ie., if I’m a brain in a vat, then it makes as much sense for me to fail to feed myself as it does to fail to feed the cat.Report

      • Avatar Glyph in reply to Murali
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        Also, Jaybird finally let the cat out of that box with the poison flask and the radioactive isotope. So he’s pretty sure he’s real now.Report

      • Avatar zic in reply to Murali
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        All I see is the smile.Report

    • Avatar Michael Drew in reply to Jaybird
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      “Kick a rock”; “Gotta feed the cats”; these are perfectly reasonable ways to deal with this problem from a day-to-day pragmatic standpoint. But they are both choices simply not to deal with it philosophically. They don’t resolve it, and they’re not an argument that there’s really no problem.

      Obviously we’re all going to avoid kicking rocks (barefoot at least). Is the world really “like” our perceptions of it? Is it “real” in that sense (again, if it were brains in vats, if that were real, then that would be real, but we would then say that the world isn’t “real”: that’s exactly, paradigmatically what we think about when we think about what it would be if it were “not real.”) Merely observing that we’re going to act like the world is how we perceive it doesn’t solve or address those questions; in fact it’s closer to admitting defeat by them.

      There is philosophical work that can be done (has been done) to deal with this problem strictly along pragmatic lines. But for moderns like us who want to think we know things, that line of work involves giving up huge amounts of theoretical territory we tend to be very reluctant to give up (i.e. accepting significant degrees of relativism about truth [EDIT: maybe more accurately, about knowledge] across vast swaths of inquiry).

      To pretend to deal with the problem of the real or unreal external world with “Kick a rock” without reckoning with what you have to give up if you really want to deal with the problem that way isn’t to deal with the problem. It’s just, “LALALALALALAICAN’THEARYOU.”Report

      • Avatar Jaybird in reply to Michael Drew
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        Don’t see it as “LALALALALALAICAN’THEARYOU” as much as “sorry, the burden of proof for this being dreams in the mind of Cthulhu before he eats us is on you, it’s not on me.”

        If, however, you’d like to argue this against the Brain in a Jar folks, I’d be more than happy enough to explain how they have the burden of proof for the Cthulhu thing prior to your having it for the Brain in a Jar thing.Report

      • Avatar Murali in reply to Michael Drew
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        @jaybird How do we decide who the burden of proof lies with?Report

      • Avatar Jaybird in reply to Michael Drew
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        Maybe on the guy who wouldn’t exist if he were right? That seems like a good rule of thumb.Report

      • Avatar Murali in reply to Michael Drew
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        Maybe its a good punchline, but you have to show how assigning burdens of evidence in this way actually gets you closer to the truth.

        Hint: it doesn’t. In the absence of all evidence the only appropriate default is complete agnosticism. Anything else would not apportion belief to evidence.Report

      • Avatar Jaybird in reply to Michael Drew
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        Can we just agree that you’re using “knowledge” differently than most folks? If you’re 100% sure of a thing, like “a right angle has 90 degrees in a flat Euclidian plane”, then it’s “knowledge” and if it’s just something that comes from the senses, like “I’m married”, then it’s just something that we have to operate around as a working assumption, to be abandoned the moment we have a reason to believe that we’re in the Matrix above and beyond the deja vu that happens all the time?

        How’s this? If you want me to abandon my working assumptions, the burden of proof is on you.Report

      • Avatar Jaybird in reply to Michael Drew
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        Now you can ask “why is the burden of proof on me?” and I can say “because you want me to change.”Report

      • Avatar Stillwater in reply to Michael Drew
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        Jaybird,

        The brain in a vat hypothesis suffices to cast doubt on even definitional mathematical truths. It leaves nothing unscathed, which is why it’s a bit of a reductio on itsownself: if the hypothesis is true, I have no way of determining that the hypothesis even might be true.Report

      • Avatar Jaybird in reply to Michael Drew
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        Huh, I always thought that stuff like “perfect spheres” and whatnot were left intact by the BIJ. I can always make up something, give it some traits, then say “I know that these other traits follow”.

        If nothing else, that certainly demonstrates why it’s so important to not be holding the hot potato that is the “burden of proof” when it comes time to discuss something that allows no evidence either for or against it.Report

      • Avatar PPNL in reply to Michael Drew
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        says:

        Can we just agree that you’re using “knowledge” differently than most folks? If you’re 100% sure of a thing, like “a right angle has 90 degrees in a flat Euclidian plane”, then it’s “knowledge”…

        That’s true by definition. I could define it differently so in what sense can this be called knowledge?

        All mathematical knowledge is arrived at by circular reasoning. You start with axioms that you do not question and derive complex proofs. But your conclusion is contained in your assumptions. That is circular reasoning. But that is how mathematical truth is defined.

        Empirical truth is defined differently but it is still a reasonable and useful definition of truth.

        In a sense mathematical truth and empirical truth are mirrors of each other. In math you start with axioms and derive complex mathematical structure. In science you start with complex empirical structure and try to derive the simple underlying axioms. In math your conclusions are absolutely true except that your reasoning is circular. In science your observations are true but your axioms are conditional and you must stand ready to abandon them.Report

      • Avatar Stillwater in reply to Michael Drew
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        says:

        Jaybird,

        Mathematical truths are necessary, so whether we’re brains in a vat or not, from our pov as not-vat-brains those truths would hold (and necessarily) in any event. But it’s possible, gven the hypothesis of vat-brains (at least those controlled by evil demons) that the experience of deriving mathematical truth or holding mathemtical beliefs is just part of the systematic delusion. Even the belief that we’re following certain “a priori knowable” rules is subject to doubt. The rules could keep changing in each application, for example, or diverge wildly from how we currently use them without there being any mechanism to determine whether we’re drawing good inferences or not (since all of em could seem like good inferences).Report

      • Avatar Murali in reply to Michael Drew
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        says:

        I don’t necessarily want you to change your views, just acknowledge that they are not fully rational. If even that counts as wanting you to change your views, then you also similarly want me to change my views. In any case, I have already provided that proof in the form of the following argument.

        P1: We should apportion belief in a proposition according to its likelihood.
        P2: Given two propositions P and ~P where both are equally consistent with the evidence but in which ~P is twice as complicated as P, the likelihood of P is 0.62
        P3: Sceptical scenarios is as consistent with the evidence as realist ones but are, in disjunction, at most twice as complicated as the corresponding disjunction of non-sceptical ones
        P4: The likelihood of the disjunct of non-sceptical scenarios is 0.62
        Conclusion: We should have 62% confidence in the proposition that the “external world is real”.Report

      • Avatar Michael Drew in reply to Michael Drew
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        says:

        @jaybird

        What you’re missing is that I’m not trying to prove the brain-in-a-vat notion. So the burden really can’t be on me. It’s on whoever wants to prove that’s not what we are (or that it is). That’s the nature of skepticism. The burden of proof is on the one wanting to claim knowledge, that’s the very nature of what we’ve defined as knowledge. If we want to admit resemblance-to-perception external-world realism is just an assumption and we don’t know it’s true, that’s great, that’s all we’re arguing for. I’m just saying that if that’s the case it’s pretty interesting and important, even though day-to-day-wise, I’m as happy to operate on the assumption of similitude between our perceptions and the world (even despite my feeling that on barest examination that is an incoherent idea). That works fine for me for day-to-day living just like it did for your professor, but it doesn’t work fine for philosophical noodling, which I like to do. If you want to make the philosophical idea that the world might be radically different from how we perceive it go away via proof that it isn’t, then you have to supply the proof. Some of us like the fascinating uncertainty that the not knowing injects into life.Report

      • Avatar Rose Woodhouse in reply to Michael Drew
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        says:

        First, I agree that the “kick a rock” or Moore’s “here is one hand” misses the point. That there is a possibility that there is no external world is real.

        There are real world implications of this. If we assume that our senses represent the world to us, we do not know exactly how our senses correlate with the object. This is a problem in philosophy of science.

        However, I honestly have no idea where you proved that abduction yields equal reason to believe that BiaV is as likely a mind-independent world that in some way correlates with our senses. (For those of you who are non-philosophers, Bertrand Russell wrote a very nice explanation of this intended for the layperson, where he explains why you cannot prove the external world exists, but abduction (not kidnapping, but inference to best explanation) gives reason to believe it. The first two chapters of The Problems of Philosophy. I assign it when I teach intro phil, usually.)

        @jaybird – Descartes introduced the evil demon to negate mathematical truths. He first asks – what if this is all a dream? That’s the basic brain-in-a-vat question. He thinks mathematical truths would still exist. He goes one step further and assumes that someone with evil intent is actually tricking him. He thinks if that were the case, then you would have to concede mathematical truths might not survive the doubt.Report

      • Avatar Michael Drew in reply to Michael Drew
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        says:

        Rose, what are you doing spending all your time in real, sunny, concretely beautiful places like gardens? We need you here, mushrooming with us in the closet of doubt, setting us straight!Report

      • Avatar Rose Woodhouse in reply to Michael Drew
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        says:

        I garden to escape from philosophy, and I philosophize to escape from gardens.

        Murali, it seems like you’re making a couple of mistakes. One is that epistemic possibility entails metaphysical possibility. This is part of what Kripke argues against. Second, you have a mereological problem. What is a moving part, and how on earth are we supposed to know how many parts it takes to make an evil demon? It seems as if on your account, there are no more moving parts than a world that is the same as the actual, but that I am omnipotent. Thus, it’s just as likely that I am omnipotent as not.Report

      • Avatar Murali in reply to Michael Drew
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        says:

        @rose-woodhouse

        One is that epistemic possibility entails metaphysical possibility.

        You’re right that I didn’t consider the distinction. But now that you brought it up, I’m not sure what argument could show that such sceptical scenarios are logically but not metaphysically possible. I’ll have to do some reading to bone up on my metaphysics. I’ll also have to think about which sense of possibility I care about. Since my goal is largely epistemic, I might want there to be possible worlds which may be metaphysically impossible but which are not known to be such given the set of experiences people have.

        Second, you have a mereological problem. What is a moving part, and how on earth are we supposed to know how many parts it takes to make an evil demon?

        By moving part, I mean independent premise (since possible worlds are just sets of sentences). Some premises posit independent entities. Other premises further specify the nature of such entities.

        ReReport

      • Avatar Chris in reply to Michael Drew
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        says:

        Things like gravity, strong force, weak force and electromagnetism are thus (at the minimum) logical objects we posit in order to make the content of our subjective experience more probable…

        Once you posit the existence of such logical objects, the expectation that future events will look like past ones is almost trivial… This solves the old problem of induction.

        Since Rose brought up abduction, I imagine you can see the problem with this part, too.

        Any story about a grue object would have to posit some such intervening cause in order to spell out what a grue object would be.

        And the problem above should illuminate the problem here. Also.Report

      • Avatar Rose Woodhouse in reply to Michael Drew
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        says:

        since possible worlds are just sets of sentences

        If this is one of your premises, I’m definitely not on board.

        Anyhow, again, even if it were true that possible worlds were sets of sentences, the possible world in which “Rose is a philosophy professor” has as many sentences as “Rose is a chimp on roller skates.”Report

      • Avatar Jaybird in reply to Michael Drew
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        says:

        In a sense mathematical truth and empirical truth are mirrors of each other. In math you start with axioms and derive complex mathematical structure. In science you start with complex empirical structure and try to derive the simple underlying axioms. In math your conclusions are absolutely true except that your reasoning is circular. In science your observations are true but your axioms are conditional and you must stand ready to abandon them.

        I totally agree with this and, for some reason, I have this categorized in the stuff that Plato was talking about. He saw mathematical truths as purer than the messy stuff our fingers are capable of drawing or nature is capable of making. It’s not, and will never be, a circle. Just an approximation… ah, but we can see the Form of the circle in our mind’s eye, can’t we? Scientific truths are stuck with how this circle is really a crappy oblong.

        He thinks if that were the case, then you would have to concede mathematical truths might not survive the doubt.

        Well, at this point, the game is given away. “Assume we have a system that is untestable even in theory. Now prove that we aren’t in this system.”

        “By definition, you can’t.”

        “HA! I WIN!”

        At that point, well… you’re stuck watching your interlocutor enjoying his spoils and now you have to feed the cat.Report

      • Avatar Jaybird in reply to Michael Drew
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        says:

        Personally, I find the question of “how do you know if other people dream when they sleep?” to be a much more fun game to play.Report

      • Avatar Stillwater in reply to Michael Drew
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        says:

        Murali,

        Since my goal is largely epistemic, I might want there to be possible worlds which may be metaphysically impossible but which are not known to be such given the set of experiences people have.

        I don’t mean this question to sound condescending but have you read Kripke on this stuff? In Naming and Necessity he talks quite about what he refers to as “qualitatively identical epistemic situations” as a way of teasing out some problems in the conceivability entails possibility line of reasoning. (There’s also a ton of secondary stuff on what that rephrasal technique means for possible worlds and the mind-body problem, etc.) Also, have you read any of Chalmer’s stuff on two dimensional semantics which tries to provide an analysis of meaning across two contexts, specifically modal contexts. His work is basically a lift from Stalnaker’s and Kaplan’s previous arguments, and even tho he basically made his entire career by pretty much repeating and systematizing what they were getting on about it’s a pretty good read.

        I’m not sure these writers will help you fill out your argument, but there is some pretty good stuff on conceivability (and what that entails) and possibility, and in what sense conceivability entails possibility.Report

      • Avatar Rose Woodhouse in reply to Michael Drew
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        says:

        Agree with Stillwater about Kripke. Also, there was a book that came out about 10 years ago called “Conceivability and Possibility” ed by Gendler and Hawthorne. The intro is a really really good overview of the issue. I found it really helpful orienting myself. Since my dissertation was on emotional responses to fictions, I had to dip a little into this stuff, since whatever a fictional character turns out to be has some bearing. (Although I don’t think it contains anything about 2D semantics…that stuff came out after, maybe…or maybe I misremember)? http://www.amazon.com/Conceivability-Possibility-Tamar-Szabo-Gendler/dp/0198250908/ref=sr_1_1?ie=UTF8&qid=1402929352&sr=8-1&keywords=conceivability+and+possibilityReport

      • Avatar Rose Woodhouse in reply to Michael Drew
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        says:

        Also, some of the essays in the book are really good. Unfortunately Greg Currie, of whom I’m usually a fan, has an essay in the book on imaginative resistance which is not his best. (Imaginative resistance is a topic I wrote on).Report

      • Avatar Murali in reply to Michael Drew
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        says:

        @rose-woodhouse
        It’s extremely unlikely that Rose the rollerskating chimp would type wonderful posts on gardening and philosophy. Given that I experience reading her posts, if Rose exists, she is almost certainly not a rollerskating chimpReport

      • Avatar Rose Woodhouse in reply to Michael Drew
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        says:

        It’s extremely unlikely that Rose the rollerskating chimp would type wonderful posts on gardening and philosophy. Given that I experience reading her posts, if Rose exists, she is almost certainly not a rollerskating chimp

        Right. And it seems quite unlikely given the way the world is that there is not a mind-independent reality. Abduction.Report

      • Avatar Murali in reply to Michael Drew
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        says:

        @rose-woodhouse

        But, the rollerskating chimp hypothesis is one that entails that I would have different experiences than the one I think I have been having while the evil demon and brain in vat hypotheses are constructed to entail that I have the same experiences I think I have had.Report

  6. Avatar zic
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    says:

    Perhaps I’m in way over my head, but:

    I’m reading Anthony Kenny’s History of Western Philosophy, nearly at the end of Book I.

    And while I realize my take is probably not an educated take, but it seems to me that the whole reason Aristotle kicked butt is that he understood the importance of leaving the ivory tower, getting out of his own head, and going out and talking to the experts who gained expertise through doing — to the weavers, the potters, the fence builders, the farmers, the cooks.

    There is some level of hubris in thinking one can understand reality without actually going out and engaging reality. Logically, it’s prey to the problem of thinking things that are fractal are linear (always a problem for the human mind; like thinking one is an individual instead of recognizing that each individual human is a complex web of living organisms, and the health of the individual rests on the health of that web).

    It’s very easy to look at a watershed and think the major river through it the thing of importance in the watershe; but it’s the fingerling trickles of water that make that river. The quality of the water in the watershed rests not on the quality of the river first, but on the health of those small, often ephemeral trickles that feed the river. You can never understand the river if you don’t understand the feeder streams, too.Report

  7. Avatar ktward
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    says:

    We thus don’t have to assume that the external world is real in order to do science or go about our daily lives. At most, we just have to acknowledge some possibility that the world we observe is real as far as daily practical problems are concerned. On the theoretical end, we just have to be careful and be modest about the claims that we can make. However, as we have seen, this does not invalidate our current scientific knowledge.

    Navel-gazing at its finest.Report

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