Brain in a vat
In philosophy
Philosophy is the study of general and fundamental problems, such as those connected with existence, knowledge, values, reason, mind, and language. Philosophy is distinguished from other ways of addressing such problems by its critical, generally systematic approach and its reliance on rational...

, the brain in a vat is an element used in a variety of thought experiment
Thought experiment
A thought experiment or Gedankenexperiment considers some hypothesis, theory, or principle for the purpose of thinking through its consequences...

s intended to draw out certain features of our ideas of knowledge, reality, truth, mind, and meaning. It is drawn from the idea, common to many science fiction
Science fiction
Science fiction is a genre of fiction dealing with imaginary but more or less plausible content such as future settings, futuristic science and technology, space travel, aliens, and paranormal abilities...

 stories, that a mad scientist
Mad scientist
A mad scientist is a stock character of popular fiction, specifically science fiction. The mad scientist may be villainous or antagonistic, benign or neutral, and whether insane, eccentric, or simply bumbling, mad scientists often work with fictional technology in order to forward their schemes, if...

, machine
A machine manages power to accomplish a task, examples include, a mechanical system, a computing system, an electronic system, and a molecular machine. In common usage, the meaning is that of a device having parts that perform or assist in performing any type of work...

 or other entity might remove a person's brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...

 from the body, suspend it in a vat of life-sustaining liquid, and connect its neurons by wires to a supercomputer
A supercomputer is a computer at the frontline of current processing capacity, particularly speed of calculation.Supercomputers are used for highly calculation-intensive tasks such as problems including quantum physics, weather forecasting, climate research, molecular modeling A supercomputer is a...

 which would provide it with electrical impulses
Action potential
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...

 identical to those the brain normally receives. According to such stories, the computer would then be simulating reality
Simulated reality
Simulated reality is the proposition that reality could be simulated—perhaps by computer simulation—to a degree indistinguishable from "true" reality. It could contain conscious minds which may or may not be fully aware that they are living inside a simulation....

 (including appropriate responses to the brain's own output) and the person with the "disembodied" brain would continue to have perfectly normal conscious experiences without these being related to objects or events in the real world.

The simplest use of brain-in-a-vat scenarios is as an argument
In philosophy and logic, an argument is an attempt to persuade someone of something, or give evidence or reasons for accepting a particular conclusion.Argument may also refer to:-Mathematics and computer science:...

 for philosophical skepticism
Philosophical skepticism
Philosophical skepticism is both a philosophical school of thought and a method that crosses disciplines and cultures. Many skeptics critically examine the meaning systems of their times, and this examination often results in a position of ambiguity or doubt...

 and solipsism
Solipsism is the philosophical idea that only one's own mind is sure to exist. The term comes from Latin solus and ipse . Solipsism as an epistemological position holds that knowledge of anything outside one's own mind is unsure. The external world and other minds cannot be known, and might not...

. A simple version of this runs as follows: Since the brain in a vat gives and receives exactly the same impulses as it would if it were in a skull, and since these are its only way of interacting with its environment, then it is not possible to tell, from the perspective of that brain, whether it is in a skull or a vat. Yet in the first case most of the person's beliefs may be true (if he believes, say, that he is walking down the street, or eating ice-cream); in the latter case they are false. Since the argument says one cannot know whether he or she is a brain in a vat, then he or she cannot know whether most of his or her beliefs might be completely false. Since, in principle, it is impossible to rule out oneself being a brain in a vat, there cannot be good grounds for believing any of the things one believes; a skeptical argument would contend that one certainly cannot know them, raising issues with the definition of knowledge.

The brain-in-a-vat is a contemporary version of the argument given in buddhist
Buddhism is a religion and philosophy encompassing a variety of traditions, beliefs and practices, largely based on teachings attributed to Siddhartha Gautama, commonly known as the Buddha . The Buddha lived and taught in the northeastern Indian subcontinent some time between the 6th and 4th...

 Maya illusion
Maya (illusion)
Maya , in Indian religions, has multiple meanings, usually quoted as "illusion", centered on the fact that we do not experience the environment itself but rather a projection of it, created by us. Maya is the principal deity that manifests, perpetuates and governs the illusion and dream of duality...

, Plato
Plato , was a Classical Greek philosopher, mathematician, student of Socrates, writer of philosophical dialogues, and founder of the Academy in Athens, the first institution of higher learning in the Western world. Along with his mentor, Socrates, and his student, Aristotle, Plato helped to lay the...

's Allegory of the Cave
Allegory of the cave
The Allegory of the Cave—also known as the Analogy of the Cave, Plato's Cave, or the Parable of the Cave—is an allegory used by the Greek philosopher Plato in his work The Republic to illustrate "our nature in its education and want of education"...

, Zhuangzi
Zhuangzi was an influential Chinese philosopher who lived around the 4th century BCE during the Warring States Period, a period corresponding to the philosophical summit of Chinese thought — the Hundred Schools of Thought, and is credited with writing—in part or in whole—a work known by his name,...

's "Zhuangzi dreamed he was a butterfly", and the evil demon in René Descartes
René Descartes
René Descartes ; was a French philosopher and writer who spent most of his adult life in the Dutch Republic. He has been dubbed the 'Father of Modern Philosophy', and much subsequent Western philosophy is a response to his writings, which are studied closely to this day...

' Meditations on First Philosophy
Meditations on First Philosophy
Meditations on First Philosophy is a philosophical treatise written by René Descartes and first published in 1641 . The French translation was published in 1647 as Méditations Metaphysiques...


Philosophical responses

Such puzzles have been worked over in many variations by philosophers in recent decades. American philosopher Hilary Putnam
Hilary Putnam
Hilary Whitehall Putnam is an American philosopher, mathematician and computer scientist, who has been a central figure in analytic philosophy since the 1960s, especially in philosophy of mind, philosophy of language, philosophy of mathematics, and philosophy of science...

 popularized the modern terminology over Descartes's "evil demon," although it brings up such complications and objections as whether the mind is reducible to the workings of a brain. Some, including Barry Stroud
Barry Stroud
Barry Stroud is a philosopher known for his work on philosophical skepticism, David Hume, and Wittgenstein, among other topics. He received a B.A. in philosophy from the University of Toronto, followed by a Ph.D. in philosophy from Harvard University, under the direction of Morton White. Since...

, continue to insist that such puzzles constitute an unanswerable objection to any knowledge claims. Hilary Putnam, in his 1981 book Reason, Truth, and History, argued against the special case of a brain born in a vat. In the first chapter of his book, Putnam claims that the thought experiment is inconsistent on the grounds that a brain born in a vat could not have the sort of history and interaction with the world that would allow its thoughts or words to be about the vat that it is in.

In other words, if a brain in a vat stated "I am a brain in a vat", it would always be stating a falsehood. If the brain making this statement lives in the "real" world, then it is not a brain in a vat. On the other hand, if the brain making this statement is really just a brain in the vat then by stating "I am a brain in a vat" what the brain is really stating is "I am what nerve stimuli have convinced me is a 'brain,' and I reside in an image that I have been convinced is called a 'vat'." That is, a brain in a vat would never be thinking about real brains or real vats, but rather about images sent into it that resemble real brains or real vats. This of course makes our definition of "real" even more muddled. This refutation of the vat theory is a consequence of his endorsement, at that time, of the causal theory of reference
Causal theory of reference
A causal theory of reference is a theory of how terms acquire specific referents. Such theories have been used to describe many referring terms, particularly logical terms, proper names, and natural kind terms...

. Roughly, in this case: if you've never experienced the real world, then you can't have thoughts about it, whether to deny or affirm them. Putnam contends that by "brain" and "vat" the brain in a vat must be referring not to things in the "outside" world but to elements of its own "virtual world"; and it is clearly not a brain in a vat in that sense. One of the other problems is that the supposed brain in a vat cannot have any evidence for being a brain in a vat, because that would be saying "I have what nerve stimuli have convinced me is evidence to my being a brain in a vat" and also "Nerve stimuli have convinced me of the fact that I am a brain in a vat".

Many writers have found Putnam's proposed solution unsatisfying, as it appears, in this regard at least, to depend on a shaky theory of meaning: that we cannot meaningfully talk or think about the "external" world because we cannot experience it; sounds like a version of the outmoded verification principle. Consider the following quote: "How can the fact that, in the case of the brains in a vat, the language is connected by the program with sensory inputs which do not intrinsically or extrinsically represent trees (or anything external) possibly bring it about that the whole system of representations, the language in use, does refer to or represent trees or any thing external?" Putnam here argues from the lack of sensory inputs representing (real world) trees to our inability to meaningfully think about trees. But it is not clear why the referents of our terms must be accessible to us in experience. One cannot, for example, have experience of other people's private states of consciousness; does this imply that one cannot meaningfully ascribe mental states to others? In effect, Putnam demonstrates that the state of being an envatted brain is invisible and indescribable from within, but it is unclear that this semantic victory goes far to address the problem in relation to knowledge.

Subsequent writers on the topic have been particularly interested in the problems it presents for content: that is, how - if at all - can the brain's thoughts be about a person or place with whom it has never interacted and which perhaps does not exist.

See also

  • Dream argument
    Dream argument
    The dream argument is the postulation that the act of dreaming provides preliminary evidence that the senses we trust to distinguish reality from illusion should not be fully trusted, and therefore any state that is dependent on our senses should at the very least be carefully examined and...

  • Evil demon
  • Experience machine
  • Externalism
    Externalism is a group of positions in the philosophy of mind which hold that the mind is not only the result of what is going on inside the nervous system but also of what either occur or exist outside the subject. It is often contrasted with internalism which holds that the mind emerges out of...

  • Internalism and externalism
    Internalism and externalism
    Internalism and externalism are two opposing ways of explaining various subjects in several areas of philosophy. These include human motivation, knowledge, justification, meaning and truth. The distinction arises in many areas of debate with similar but distinct meanings...

  • Neurally controlled animat
    Neurally controlled animat
    A Neurally Controlled Animat is the conjunction of#a cultured neuronal network#a virtual body, the Animat, "living" in a virtual computer generated environment, connected to this array...

  • Simulated reality
    Simulated reality
    Simulated reality is the proposition that reality could be simulated—perhaps by computer simulation—to a degree indistinguishable from "true" reality. It could contain conscious minds which may or may not be fully aware that they are living inside a simulation....

  • Skeptical hypothesis
  • Solipsism
    Solipsism is the philosophical idea that only one's own mind is sure to exist. The term comes from Latin solus and ipse . Solipsism as an epistemological position holds that knowledge of anything outside one's own mind is unsure. The external world and other minds cannot be known, and might not...

  • Technological singularity
    Technological singularity
    Technological singularity refers to the hypothetical future emergence of greater-than-human intelligence through technological means. Since the capabilities of such an intelligence would be difficult for an unaided human mind to comprehend, the occurrence of a technological singularity is seen as...

Cultural references

  • Cold Lazarus
    Cold Lazarus
    Cold Lazarus is a four-part British television drama written by Dennis Potter with the knowledge that he was dying of cancer of the pancreas....

  • Donovan's Brain (film)
    Donovan's Brain (film)
    Donovan's Brain is a 1953 film, starring Lew Ayres, Gene Evans, and Nancy Reagan , based on the 1942 horror novel Donovan's Brain by Curt Siodmak.-Plot:...

  • Futurama
    Futurama is an American animated science fiction sitcom created by Matt Groening and developed by Groening and David X. Cohen for the Fox Broadcasting Company. The series follows the adventures of a late 20th-century New York City pizza delivery boy, Philip J...

  • The Matrix (series)
  • Source Code (film)
    Source Code (film)
    Source Code is a 2011 American science fiction-techno-thriller film directed by Duncan Jones, written by Ben Ripley, starring Jake Gyllenhaal, Michelle Monaghan, Vera Farmiga, Russell Peters and Jeffrey Wright...

  • Spock's Brain episode of Star Trek
    Star Trek
    Star Trek is an American science fiction entertainment franchise created by Gene Roddenberry. The core of Star Trek is its six television series: The Original Series, The Animated Series, The Next Generation, Deep Space Nine, Voyager, and Enterprise...

  • Inception
    Inception: The Subconscious Jams 1994-1995 is a compilation of unreleased tracks by the band Download.-Track listing:# "Primitive Tekno Jam" – 3:23# "Bee Sting Sickness" – 8:04# "Weed Acid Techno" – 8:19...

  • The Thirteenth Floor
    The Thirteenth Floor
    The Thirteenth Floor is a 1999 science fiction film directed by Josef Rusnak and loosely based upon Simulacron-3 , a novel by Daniel F. Galouye...

  • Dark Star
    Dark Star (film)
    Dark Star is a 1974 American comedic science fiction motion picture directed by John Carpenter and co-written with Dan O'Bannon.-Backstory and plot:...

  • Gangers in Doctor Who
    Doctor Who
    Doctor Who is a British science fiction television programme produced by the BBC. The programme depicts the adventures of a time-travelling humanoid alien known as the Doctor who explores the universe in a sentient time machine called the TARDIS that flies through time and space, whose exterior...

  • See episode 11 in the 3rd season of the cartoon show 'American Dad!' The plot constitutes an argument in favor of our being, at least sometimes, only brains in a vat. Doing so makes for better vacations. Go to

External links

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