Brains in Vats and the Evil Demon

Matrix Readings

Before breaking out of the Matrix, Neo's life was not what he thought it was. It was a lie. Morpheus described it as a "dreamworld," but unlike a dream, this world was not the creation of Neo's mind. The truth is more sinister: the world was a creation of the artificially intelligent computers that have taken over the Earth and have subjugated mankind in the process.

These creatures have fed Neo a simulation that he couldn't possibly help but take as the real thing. What's worse, it isn't clear how any of us can know with certainty that we are not in a position similar to Neo before his "rebirth." Our ordinary confidence in our ability to reason and our natural tendency to trust the deliverances of our senses can both come to seem rather naive once we confront this possibility of deception.

A viewer of The Matrix is naturally led to wonder: how do I know I am not in the Matrix? How do I know for sure that my world is not also a sophisticated charade, put forward by some super-human intelligence in such a way that I cannot possibly detect the ruse? The philosopher Rene Descartes suggested a similar worry: the frightening possibility that all of one's experiences might be the result of a powerful outside force, a "malicious demon."

"And yet firmly implanted in my mind is the long-standing opinion that there is an omnipotent God who made me the kind of creature that I am. How do I know that he has not brought it about that there is no earth, no sky, no extended thing, no shape, no size, no place, while at the same time ensuring that all these things appear to me to exist just as they do now?

What is more, just as I consider that others sometimes go astray in cases where they think they have the most perfect knowledge, how do I know that God has not brought it about that I too go wrong every time I add two and three or count the sides of a square, or in some even simpler matter, if that is imaginable?

But perhaps God would not have allowed me to be deceived in this way, since he is said to be supremely good; [...] I will suppose therefore that not God, who is supremely good and the source of truth, but rather some malicious demon of the utmost power and cunning has employed all his energies in order to deceive me. I shall think that the sky, the air, the earth, colours, shapes, sounds and all external things are merely the delusions of dreams which he has devised to ensnare my judgment." (Meditations, 15)

The narrator of Descartes' Meditations concludes that none of his former opinions are safe. Such a demon could not only deceive him about his perceptions, it could conceivably cause him to go wrong when performing even the simplest acts of reasoning.

This radical worry seems inescapable. How could you possibly prove to yourself that you are not in the kind of nightmarish situation Descartes describes? It would seem that any argument, evidence or proof you might put forward could easily be yet another trick played by the demon. As ludicrous as the idea of the evil demon may sound at first, it is hard, upon reflection, not to share Descartes' worry: for all you know, you may well be a mere plaything of such a malevolent intelligence. More to the point of our general discussion: for all you know, you may well be trapped in the Matrix.

Many contemporary philosophers have discussed a similar skeptical dilemma that is a bit closer to the scenario described in The Matrix. It has come to be known as the "brain in a vat" hypothesis, and one powerful formulation of the idea is presented by the philosopher Jonathan Dancy:

"You do not know that you are not a brain, suspended in a vat full of liquid in a laboratory, and wired to a computer which is feeding you your current experiences under the control of some ingenious technician scientist (benevolent or malevolent according to taste). For if you were such a brain, then, provided that the scientist is successful, nothing in your experience could possibly reveal that you were; for your experience is ex hypothesi identical with that of something which is not a brain in a vat. Since you have only your own experience to appeal to, and that experience is the same in either situation, nothing can reveal to you which situation is the actual one." (Introduction to Contemporary Epistemology, 10)

If you cannot know whether you are in the real world or in the word of a computer simulation, you cannot be sure that your beliefs about the world are true. And, what was even more frightening to Descartes, in this kind of scenario it seems that your ability to reason is no safer than the deliverances of the senses: the evil demon or malicious scientist could be ensuring that your reasoning is just as flawed as your perceptions.

As you have probably already guessed, there is no easy way out of this philosophical problem (or at least there is no easy philosophical way out!). Philosophers have proposed a dizzying variety of "solutions" to this kind of skepticism but, as with many philosophical problems, there is nothing close to unanimous agreement regarding how the puzzle should be solved.

Descartes' own way out of his evil demon skepticism was to first argue that one cannot genuinely doubt the existence of oneself. He pointed out that all thinking presupposes a thinker: even in doubting, you realize that there must at least be a self which is doing the doubting. (Thus Descartes' most famous line: "I think, therefore I am.") He then went on to claim that, in addition to our innate idea of self, each of us has an idea of God as an all-powerful, all-good, and infinite being implanted in our minds, and that this idea could only have come from God. Since this shows us that an all-good God does exist, we can have confidence that he would not allow us to be so drastically deceived about the nature of our perceptions and their relationship to reality. While Descartes' argument for the existence of the self has been tremendously influential and is still actively debated, few philosophers have followed him in accepting his particular theistic solution to skepticism about the external world.

One of the more interesting contemporary challenges to this kind of skeptical scenario has come from the philosopher Hilary Putnam. His point is not so much to defend our ordinary claims to knowledge as to question whether the "brain in a vat" hypothesis is coherent, given certain plausible assumptions about how our language refers to objects in the world. He asks us to consider a variation on the standard "brain in a vat" story that is uncannily similar to the situation described in The Matrix:

"Instead of having just one brain in a vat, we could imagine that all human beings (perhaps all sentient beings) are brains in a vat (or nervous systems in a vat in case some beings with just nervous systems count as ‘sentient’). Of course, the evil scientist would have to be outside? or would he? Perhaps there is no evil scientist, perhaps (though this is absurd) the universe just happens to consist of automatic machinery tending a vat full of brains and nervous systems.

This time let us suppose that the automatic machinery is programmed to give us all a collective hallucination, rather than a number of separate unrelated hallucinations. Thus, when I seem to myself to be talking to you, you seem to yourself to be hearing my words…. I want now to ask a question which will seem very silly and obvious (at least to some people, including some very sophisticated philosophers), but which will take us to real philosophical depths rather quickly. Suppose this whole story were actually true. Could we, if we were brains in a vat in this way, say or think that we were?" (Reason, Truth, and History, 7)

Putnam's surprising answer is that we cannot coherently think that we are brains in vats, and so skepticism of that kind can never really get off the ground. While it is difficult to do justice to Putnam’s ingenious argument in a short summary, his point is roughly as follows:

Not everything that goes through our heads is a genuine thought, and far from everything we say is a meaningful utterance. Sometimes we get confused or think in an incoherent manner — sometimes we say things that are simply nonsense. Of course, we don't always realize at the time that we aren't making sense — sometimes we earnestly believe we are saying (or thinking) something meaningful. High on Nitrous Oxide, the philosopher William James was convinced he was having profound insights into the nature of reality — he was convinced that his thoughts were both sensical and important. Upon sobering up and looking at the notebook in which he had written his drug-addled thoughts, he saw only gibberish.

Just as I might say a sentence that is nonsense, I might also use a name or a general term which is meaningless in the sense that it fails to hook up to the world. Philosophers talk of such a term as "failing to refer" to an object. In order to successfully refer when we use language, there must be an appropriate relationship between the speaker and the object referred to. If a dog playing on the beach manages to scrawl the word "Ed" in the sand with a stick, few would want to claim that the dog actually meant to refer to someone named Ed. Presumably the dog doesn’t know anyone named Ed, and even if he did, he wouldn’t be capable of intending to write Ed’s name in the sand. The point of such an example is that words do not refer to objects "magically" or intrinsically: certain conditions must be met in the world in order for us to accept that a given written or spoken word has any meaning and whether it actually refers to anything at all.

Putnam claims that one condition which is crucial for successful reference is that there be an appropriate causal connection between the object referred to and the speaker referring. Specifying exactly what should count as "appropriate" here is a notoriously difficult task, but we can get some idea of the kind of thing required by considering cases in which reference fails through an inappropriate connection: if someone unfamiliar with the film The Matrix manages to blurt out the word "Neo" while sneezing, few would be inclined to think that this person has actually referred to the character Neo. The kind of causal connection between the speaker and the object referred to (Neo) is just not in place. For reference to succeed, it can’t be simply accidental that the name was uttered. (Another way to think about it: the sneezer would have uttered "Neo" even if the film The Matrix had never been made.)

The difficulty, according to Putnam, in coherently supposing the brain in a vat story to be true is that brains raised in such an environment could not successfully refer to genuine brains, or vats, or anything else in the real world. Consider the example of someone who has lived their entire life in the Matrix: when they talk of "chickens," they don’t actually refer to real chickens; at best they refer to the computer representations of chickens that have been sent to their brain. Similarly, when they talk of human bodies being trapped in pods and fed data by the Matrix, they don’t successfully refer to real bodies or pods — they can’t refer to physical bodies in the real world because they cannot have the appropriate causal connection to such objects.

Thus, if someone were to utter the sentence "I am simply a body stuck in a pod somewhere being fed sensory information by a computer" that sentence would itself be necessarily false. If the person is in fact not trapped in the Matrix, then the sentence is straightforwardly false. If the person is trapped in the Matrix, then he can't successfully refer to real human bodies when he utters the words "human body," and so it appears that his statement must also be false. Such a person seems thus doubly trapped: incapable of knowing that he is in the Matrix, and even incapable of successfully expressing the thought that he might be in the Matrix! (Could this be why at one point Morpheus tells Neo that "no one can be told what the Matrix is"?)

Putnam's argument is controversial, but it is noteworthy because it shows that the kind of situation described in The Matrix raises not just the expected philosophical issues about knowledge and skepticism, but more general issues regarding meaning, language, and the relationship between the mind and the world.