The Brain in a Vat (and the problem of other minds)
1. The Brain in the Vat: The Cartesian dreaming and evil demon arguments have gotten a contemporary update. Consider the following scenario:
You stumble upon a secret laboratory full of scientists. A friend of yours lies unconscious on an operating table. The scientists are removing his brain. They submerge the brain in a vat of fluid nutrients, and then attach various wires to the brain. The scientists see you, and one of them begins to speak:
“We have the ability to stimulate this brain to make it think whatever we want it to think,” the scientist says. “Right now, your friend thinks he is walking to work. But, he is not. The things that this brain is experiencing are all merely the result of a computer simulation—but one that is SO real, that he cannot tell it apart from reality. Your friend thinks he is arriving at work now, but—as you can see—he is actually lying on an operating table without his brain.”
You are stunned, and don’t know what to do. Before you can even grapple with what you’ve just been told, the scientist says one more thing:
“Actually, that is not the whole truth. The truth is that none of THIS is real. Nothing you are experiencing RIGHT NOW is real. For, we abducted you three months ago and removed YOUR brain. Right now, your brain is actually submerged in a vat of nutrients, being stimulated by a computer program to make you think that you are seeing your friend having his brain removed. We figured that programming this experience for you was the easiest way to let you know what we’ve done to you. And now you know the truth.”
Question: What would you do if this happened to you? Would you believe them? How could you know for sure if they were lying? If the computer is really capable of making you experience a reality that is JUST AS REAL as the REAL reality—as the scientists claim—then life in the vat would be indistinguishable from life in reality. You would have no way to prove them wrong.
External World Skepticism: Furthermore, for all you know, perhaps it is the case that YOU are merely a brain in a vat RIGHT NOW, and nothing you experience is real. How would you be able to know if you weren’t? Ask yourself this:
Do you KNOW that you are not dreaming, or a brain in a vat, right now? If so, how?
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There seems to be NO WAY for you to prove with absolute certainty that the things you are experiencing right now are real. Recall that Locke believed that there MUST be external objects which are causing our sensations because this was the best explanation of our sensations. But, isn’t this exactly what a BIV would ALSO think to itself? For, any evidence of the external world that you think you might have would be EXACTLY the same sort of evidence that a brain in a vat would have! In the end, something like the following argument arises:
1. If you cannot know that you are not merely a brain in a vat, then you do not know that you have hands. 2. You cannot know that you are not merely a brain in a vat. 3. Therefore, you do not know that you have hands (nor, in fact, ANYTHING about the things in the world around you; the objects of your experiences).
On Premise 1: Why think that premise 1 is true? It derives from the following principle:
The Closure Principle: If you know P, and P entails Q, then you can know Q.
But, let P = and Q = . If I KNOW that I have hands, then this ENTAILS that I am not a brain in a vat. So, by the Closure Principle:
If you know that you have hands, then you can know that you are not a BIV.
Premise 1 is just the contrapositive of this; i.e.,
(i) If you are 21 or older, then you can legally drink alcohol. (ii) If you cannot legally drink alcohol, then you are not 21 or older.
Other Skeptical Scenarios: Nagel gives another sort of skeptical scenario, which is originally from Bertrand Russell:
There is no logical impossibility in the hypothesis that the world sprang into being five minutes ago, exactly as it then was, with a population that “remembered” a wholly unreal past. There is no logically necessary connection between events at different times; therefore nothing that is happening now or will happen in the future can disprove the hypothesis that the world began five minutes ago. (Analysis of Mind, 1921)
Do you know that you were not merely created 5 minutes ago, with false memories of a past that never happened? In principle, there is no way to verify that this is not the case.
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2. The Problem of Other Minds: Here’s an interesting problem that arises even if you reject external world skepticism. Imagine that you believe that there ARE external objects outside of your head, and even that they are very similar to the way that we experience them—and that we are even justified in believing so. Nevertheless, this question remains:
How do you know that anyone else is conscious?
Take a step back: At the very least, how can you be sure that everyone else experiences secondary qualities in the same way that you do? For instance, how do I know whether, when you look at a ripe tomato, to you it looks like THIS:
All I have access to is your external behavior. Sure, when I ask you what color the tomato is, you’ll CALL it ‘red’ – but you would do so even if it looked like the tomato above, because you would have been brought up in a society which pointed at things like ripe tomatoes, rubies, red delicious apples, and red roses and taught you to apply the label ‘red’ to things that looked like that. (This video nicely illustrates this point; from start to 2:15)
And sure, when we cut people open and examine their internal organs, their eyes and brains seem to function in pretty much the same way. But, can you really KNOW that other people experience the world in the same way that you do?
Actually, we’re quite sure that some people do NOT experience secondary qualities in quite the same way. For instance, some people are color blind. Others are supertasters (and it’s certainly common for some to easily detect or identify certain smells or flavors in dishes, which others cannot). Younger people can hear higher frequencies. We all have different aesthetic tastes (e.g., something tastes delicious to you, but terrible to someone else). So, we’re fairly sure that experience of the world differs at least A LITTLE from person to person. But, how can we be sure that it doesn’t differ A LOT?
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Solipsism: Or worse still, how can you be sure that other people are even CONSCIOUS? Perhaps everyone around you is merely what is called a “philosophical zombie”—that is, a being which is completely indistinguishable from a conscious human being, but which actually has no conscious experiences whatsoever.
If you were living in a P-Zombie world, you would have EXACTLY the same evidence of other people being conscious as you would have in a world full of conscious people!
This is a path toward solipsism, or the view that one is the only conscious individual in existence. (An extreme form of this being that you are the ONLY THING that exists; e.g., everything else is just a product of your mind.)
[Fun side note: Do you think philosophical zombies are metaphysically possible? If so, then you might be committed to mind-body dualism! This is the whole reason that P- Zombies were discussed in the first place. The argument goes, that, if you are a Physicalist who thinks that consciousness is nothing more than matter arranged in a certain way, then it should follow that, whenever matter is arranged in exactly that same way, consciousness arises. But, since it is metaphysically possible for this to NOT be the case, then consciousness is not reducible to mere matter. Mind is more than matter. The argument goes:
1. If Physicalism is true, then any possible world which is physically identical to our own world is one where there are conscious beings. 2. But, there is a metaphysically possible world that is physically indistinguishable from ours, but where there are no conscious beings (i.e., a P-Zombie world is metaphysically possible). 3. Therefore, Physicalism is false (i.e., consciousness is not purely physical).
In short, by entertaining the Problem of Other Minds, you may have inadvertently committed yourself to some form of Dualism!]
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