Consider one of the most famous modern examples of this problem, Gilbert Harman's "Brain-in-a-Vat" thought experiment.[1] A descendant of Rene Descartes' "evil demon" hypothesis[2], this thought experiment is designed to motivate general skepticism about sense perception and the external world. What if, we are asked to imagine, you're not really here right now, but instead you are just a disembodied brain, suspended in fluid, with a complex computer stimulating your brain in all the right places to artificially create the experiences you take yourself to be having. For example, the computer could send signals to your visual cortex making you think you’re looking at a blog post on The Dance of Reason, when in fact you’re looking at no such thing, because you have no eyes. Hypothetically, the thought experiment says, there would be no way to tell the difference between a reality where your brain is directly stimulated in this way, and one where you actually have a body that interacts with the world at large. Given this indistinguishability, how can we ever really rely on our senses? How can we ever have any kind of empirical knowledge at all?
Many late-night hours have been spent trying to answer this skeptical riddle. As an intellectual puzzle, an amusing game to getting us thinking, or to kick start a conversation in an intro to philosophy course, it works just fine. But as a tool for trying to understand how humans know the world, it is deeply misleading.
The problem, in short, is that neurologically speaking conscious experience simply does not work the way this thought experiment presumes it does. The brain is a necessary, but not sufficient condition for having experiences. This is not because, as Descartes argued, we have some nonphysical aspect to our mental lives, but rather because a disembodied brain is physiologically incapable of producing the panoply of experiences that we all have every day.
Consider, for example, emotions. While the processing of emotions takes place in the brain the key ingredients that make up the neurocorrelates of emotions—hormones and neurotransmitters—are created by the endocrine system, the network of glands distributed throughout the body.[3] Without these glands you would never feel love, anger, sorrow, joy, lust, hunger or disgust. The absence of these feelings would be a dead giveaway that you were a disembodied brain in a vat.[4]
But it doesn’t stop there. In addition to an endocrine system, you would need circulatory and lymphatic systems to transport the hormones from the glands to the (very specific!) parts of the brain where they are needed in order to give rise to specific emotions. You would also need a digestive system to get the chemical precursors that fuel the endocrine system, while your integumentary system (skin, hair) is essential for flushing byproducts the other systems can’t use. Lastly, all those organs need to be supported by something, making a skeletal system indispensible as well.
In short, the only way to build a brain in a vat is to make the vat out of a human body.
I suspect two objections are occurring in your brain right now. First off, how do I know we need these systems to feel emotions? What if I only think that because the evil genius programming the computer controlling my brain has led me to believe this in the first place? Haven’t I failed to take the force of the skeptical argument seriously?
Okay, I reply, but how do we know we even need a brain in the first place? Why doesn’t the thought-experiment work if it’s just a vat and a computer? For that matter, how do we know there are such things as vats or computers or evil geniuses at all? In order to be expressible in language the thought experiment has to be grounded in something, some kind of experience that explains how our experiences might be systematically misled. If the skeptic can help themselves to a host of experience-based ideas to fund their thought experiment it seems disingenuous of them to object when I do the same to defund it.
The second objection charges me with taking the thought experiment too literally. The point of the thought experiment was to explore epistemology and the limits of our sense perception, not the neuroanatomical foundations of our emotions. We can acknowledge the facts about the physiological basis for hormones and still benefit from pondering fantastic hypotheticals such as these.
This objection precisely illustrates the problem with thought experiments I mentioned in the first paragraph. Epistemology is not bounded by the limits of our imaginations alone. Human beings come to know things by using our brains and bodies, and the empirical realities of those brains and bodies places constraints on what knowledge can be, how it can work, and how we can attain it. When we abstract away from real flesh-and-neuron human beings we are left with nothing human in our epistemology. Whatever is leftover has little bearing on anything worth caring about.
Thought experiments that are accountable only to our imaginations are unlikely to provide us with insight into complex topics like the true nature of minds, morality or metaphysics. As Daniel Dennett says, “The utility of a thought experiment is inversely proportional to the size of its departures from reality.”[5] If we want to contemplate skepticism and the limits of sense perception, there are plenty of ways to engineer realistic thought experiments based on the real-world limitations of the human brain.
Garret Merriam
Department of Philosophy
University of Southern Indiana
[2] Descartes, René, (1641), The Meditations Concerning First Philosophy, (John Veitch trans., The Online Library of Liberty 1901 Meditation II, paragraph 2.
[3] Ironically, the endocrine system includes the pineal gland, which Rene Descartes speculated was the point of contact between our immaterial minds and our material brains. Rather than serving as a magic intermediary between two metaphysical planes, the pineal gland is part of what grounds the brain squarely within the body itself.
[4] It is only fair to mention that three parts of the endocrine system—the hypothalamus, the pituitary gland, and the pineal gland—are technically housed inside the brain. The supporter of the Brain-in-a-Vat argument could perhaps lay fair claim to these, as they would be included in the terms of the original thought experiment. None the less, the other parts of the endocrine system (including the thyroid, the adrenal glands, the gonads, and other glands) are distributed throughout the body placing them well out of play for the original thought experiment.
[5] Dennett, Daniel C. (2014), Intuition Pumps and Other Tools for Thinking, p.183, Norton, W.W. & Company, Inc.
I suppose we both can agree that our brain causes our mind, and that our brain wouldn’t do this if its endocrine system broke down. But that’s just OUR brain. I can easily imagine that in principle a vat brain can make do with an artificial substitute for an endocrine system, so that the artificial system helps a vat brain cause an ordinary mind very much like ours. Can’t you imagine this, even if it is ridiculously beyond the technical capabilities of current neuroscience? That is, perhaps in principle, with enough complex programming controlling the vat brain’s inputs and outputs and controlling the flow of chemicals in each brain cell, the vat brain could have a mind that feels emotions. If so, the problem of skepticism rises like a Phoenix from the ashes.
ReplyDeleteHi Brad, thanks for the reply.
DeleteYes, I can imagine this, and that counts for something. (If I couldn't imagine it, I would likely dismiss it out of hand.) But at the same time, I'm not sure how much it counts. I can imagine a whole host of things that give us no insight into the reality of things, or even worse, things that would lead us away from an understanding of that reality if we entertained them too seriously.
For example: I can imagine it being the case that we don't need a brain for consciousness at all. Perhaps rocks are just as conscious as we are, that they think and feel just as we do. But I don't think we should spend too much of our time or effort using such a possibility as a point of departure for our studies into philosophy of mind (much less ethics or geology).
If all you mean when you say skepticism rises from the ashes is to say I have not deductively disproven skepticism, I will concede the point. But I likewise cannot deductive disprove the claim that stones are conscious. If failure to deductively disprove a claim is the threshold for requiring serious intellectual consideration of that claim, then we have a very, very long list of prima facie ridiculous things that demand our consideration, and the Brain-in-a-Vat hypothesis is probably going to be pretty low on that list.
Given your last sentence, I'm having trouble seeing the consequences of agreeing with you. As you note, there are any number of skeptical hypotheses in which I am embodied, and so these problems do not arise. Suppose we agree to talk only about those hypotheses when doing epistemology. What follows? Is there some argument or objection that no longer works? What false understanding or needless confusion do we thereby avoid?
ReplyDeletePut another way, the Brain-in-a-Vat, demon, Matrix, dream, etc. hypotheses all seem to have roughly equal utility in exploring epistemological questions, despite departing from reality to wildly different degrees. Why doesn't this show that Dennett's principle is false?
Fair questions, Brandon, I'll try to answer them.
DeleteWhether or not the Brain-in-a-Vat hypothesis has 'equal utility' to a more neurologically realistic skeptical scenario depends, I think, on what we're trying to do with it. Like I said, if all we're trying to do is get a group of intro to philosophy students thinking and talking about Descartes, I agree BiV works just fine. But if we're really trying to understand the nature of knowledge as we know it, as it actually works in the real world, I think it's a distraction.
By way of contrast, let's consider a phenomena like anosognosia. This is a real condition that makes people incapable of realizing their body is seriously impaired. Something is clearly going wrong in the brain of people with anosognosia. If we investigate what that is, we can learn a lot about how human beings come to know their own bodies, what empowers us to have kinesthetic knowledge, and what at least some of the limitations of such knowledge is. That seems like a much more profitable series of questions to ask. If, that is, what we're trying to understand is how our brains and bodies come to know things.
Interesting post Garret. I share your wariness about the use of some thought experiments... but not this one.
ReplyDeleteFirstly, as Brad noted, it's irrelevant whether part or the whole of a human is required for this thought experiment to work, since it primarily directs doubt towards the external world and the veridicality of our experiences.
Secondly, you said: "When we abstract away from real flesh-and-neuron human beings we are left with nothing human in our epistemology. Whatever is leftover has little bearing on anything worth caring about." You are right to suggest that we might be computers or something else, rather than the humans with brains that we seem to be. But, you are wrong to suggest we shouldn't care about these possibilities. You argue that we should only care about thought experiments about humans with brains because that is what we are. But this just ASSUMES that we are humans with brains. If we can learn anything from these skeptical hypotheses, it is that there is very little we can be sure of, including that apparent fact that we are humans with brains.
When assessing the value of thought experiments, i think it pays to ask first what the goal is (what is the question that we want to answer), and then check whether a thought experiment can help us answer the question without eliciting biased responses.
I fully agree with you, Dan, when you say "When assessing the value of thought experiments, i think it pays to ask first what the goal is (what is the question that we want to answer), and then check whether a thought experiment can help us answer the question without eliciting biased responses."
DeleteBut I think it works the other direction, too. That is, the questions we ought to want to answer can be checked by whether or not the thought experiment (or any other such course of investigation) can effectively shed light on those questions. The BiV scenario is structured such that (seemingly) no kind of test, imaginary or otherwise, can ever disabuse us of the premise. To steal a phrase from William James, "every difference must make a difference." If a thought experiment survives counterargument only by being immune to every possible state of affairs, then it seems to me that any questions that such a thought experiment can answer will perforce be divorced from every possible state of affairs.
Thanks Garret, this is interesting. I have some sympathy with all the commenters above, but also with your skepticism about this particular thought experiment. You say:
ReplyDeleteThe only way to build a brain in a vat is to make the vat out of a human body.
I agree with Brad that we don't really know that, but I think the important point you make here is that on our current theory we are ARE brains in vats. The vat is the human body. The BIV thought experiment asks whether we might be radically mistaken about the type of vat we are in. To me this is just not a very interesting question for a few different reasons.
First, it doesn’t really matter what kind of vat it is. Whether it is a glass vat or a human body, the question is the same: How on earth does the brain convert a bunch of electrical impulses into a point of view? If the BIV thought experiment helps someone to understand how fundamentally mysterious this is, then fine. But people should see that it is no less mysterious on the assumption that the brain is embodied than that it is embivved.
Second, the BIV thought experiment is framed in terms of possibility. Sure it’s possible that I am a BIV, but that by itself is not a reason to assign it a non zero credence. Other skeptical scenarios such as Boltzmann brains or Bostrom’s simulation argument give interesting reasons for assigning a remarkably high probability to these skeptical scenarios. If someone were, like Bostrom, to give a compelling argument that an advanced civilization might have an interest in putting trillions and trillions of brains into nutrient baths, the BIV hypothesis would be more interesting to me.
Third, I think you are completely right to focus our attention on how a brain actually works. It’s very likely that other brain-related thought experiments like qualia inversion and philosophical zombies seem logically possible simply because of our ignorance of this. They are basically just appeals to personal credulity. Along the same lines, I think it’s important to be aware of why we think we have brains in the first place. Currently we think that brains evolved to make it possible to reap the benefits of motion while avoiding its dangers. This theory might be wrong, but if it is right, then it means that the more we learn about how the brain manages this incredibly complicated task, the less coherent will be thought experiments that ask us to conceive of it functioning normally in an entirely different context.
Hi Randy,
DeleteI'm gratified (but not surprised) that we have some common ground here. Thanks for adding the point about the evolutionary function of brains. That adds a layer I hadn't considered before.
If by 'know' you mean 'have absolute certainty', then I agree that I don't know that 'the only way to build a brain in a vat is to make it out of a human body.' But by that standard, I'm not really sure anyone knows anything (or at least not anything that isn't a tautology.) Perhaps one thing we can learn from BiV scenarios is that this definition of 'knows' isn't a very fruitful one.
I think you're asking the right question when you say "How on earth does the brain convert a bunch of electrical impulses into a point of view?" But I disagree with what follows: "If the BIV thought experiment helps someone to understand how fundamentally mysterious this is, then fine."
While BiV may help someone appreciate the mystery of the mind, I think it might do so at the expense of obscuring possible solutions to that mystery. Like I said, it's fine perhaps for undergrads as an appetizer to the topic, but beyond that I fear it is a waste of epistemic resources. Every journal article written, every dissertation defended, every book published that is predicated on thought experiments like this not only is the culmination of time that could have been spent on more pragmatic problems, but may also becloud an already perplexing topic.
I have some pretty critical words for Bostrom's simulation argument, too, but that perhaps is a topic for another day. (Oh, and I'm totally stealing 'embivved', by the way.)
Garret,
ReplyDeleteSo, you say to Dan:
"The BiV scenario is structured such that (seemingly) no kind of test, imaginary or otherwise, can ever disabuse us of the premise. To steal a phrase from William James, "every difference must make a difference." If a thought experiment survives counterargument only by being immune to every possible state of affairs, then it seems to me that any questions that such a thought experiment can answer will perforce be divorced from every possible state of affairs."
And, you say to Randy:
If by 'know' you mean 'have absolute certainty', then I agree that I don't know that 'the only way to build a brain in a vat is to make it out of a human body.' But by that standard, I'm not really sure anyone knows anything (or at least not anything that isn't a tautology.) Perhaps one thing we can learn from BiV scenarios is that this definition of 'knows' isn't a very fruitful one.
I think this is a pretty important epistemological lesson, and the main reason I think BiVs are useful. But they're useful in this way *just because* they can be structured so that they turn out to be immune from every possible seeming state of affairs.
I'm thinking that you would agree with this?
Yes, I have no problem using BiVs to demonstrate that some folk concepts (like 'knows means certain') are unworkable. If this is all BiVs were used for, I would sing their praises. But I don't think this is a common use for them. But perhaps I haven't been talking to the right philosophers.
DeleteGarret, hello from your friendly neighborhood dualist. (Substance, not property. Aristotelian, not Cartesian. In case folks care.)
ReplyDeleteI have a slightly different take on BiV stuff, which may reflect my sympathies with Brad's reply--and I suspect may tie in with traditional mind-body debates (about dualisms/physicalisms/functionalisms) rather than the broader epistemological debates (about knowledge/certainty etc).
Imagine two molecularly identical human individuals, both standing next to each other (perhaps in a "vat" if you please). Their neurons are firing in the relevantly similar ways--indeed, indistinguishable ways. And so they are functioning in relevantly similar ways.
Now assume one of them is you, but the other one is not. How could you ever tell which one is you?
I suppose that the question is meant to point at how no third-person description or test would help break the tie. And yet there is a fact of the matter about which one is you. So there is a fact which no third-person description of the world can tell us about. And that's kind of interesting to know, right?
Maybe that's what BiV scenarios are really getting at: the indispensability of the first-person point of view, the irreducibility of the first-person point of view, the necessity of subjectivity for getting a complete picture of the world.
Hi Russell,
DeleteThat seems like an unconventional use of BiV, but I'll roll with it.
I agree that the first-person point of view is indispensable, but disagree about how you reach this conclusion. Your 'molecular twin' example falls prey to a similar objection that BiV does in my original post: it simply isn't possible to have two systems be perfect duplicates like that. We can't even get two hydrogen atoms to sync up like that, much less a whole human being composed of ~7,000,000,000,000,000,000,000,000,000 atoms. Any intuitions we might have about the identity conditions of two such beings should be treated with extreme skepticism, in my opinion. We simply don't live in a world where that kind of thing is possible, and as such have no basis for drawing conclusions about it.
So yes, by all means let's consider and discuss the importance of the first-person point of view. But let's do so using conceptual tools that actually connect to the world--as seen from both third and first-person points of view--rather than tools created in the depths of our unaccountable imaginations.