Brain in a vat

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A brain in a vat that believes it is walking

In philosophy, the brain in a vat (BIV) is a scenario used in a variety of thought experiments intended to draw out certain features of human conceptions of knowledge, reality, truth, mind, consciousness, and meaning. It is a modern incarnation of René Descartes's evil demon thought experiment originated by Gilbert Harman.[1] Common to many science fiction stories, it outlines a scenario in which a mad scientist, machine, or other entity might remove a person's brain from the body, suspend it in a vat of life-sustaining liquid, and connect its neurons by wires to a supercomputer which would provide it with electrical impulses identical to those the brain normally receives.[2] According to such stories, the computer would then be simulating reality (including appropriate responses to the brain's own output) and the "disembodied" brain would continue to have perfectly normal conscious experiences, such as those of a person with an embodied brain, 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 for philosophical skepticism[3] and solipsism. 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 they believe, say, that they are walking down the street, or eating ice-cream); in the latter case, their beliefs are false. Since the argument says one cannot know whether one is a brain in a vat, then one cannot know whether most of one's 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. Other philosophers have drawn upon sensation and its relationship to meaning in order to question whether brains in vats are really deceived at all,[4] thus raising wider questions concerning perception, metaphysics, and the philosophy of language.

The brain-in-a-vat is a contemporary version of the argument given in Hindu Maya illusion, Plato's Allegory of the Cave, Zhuangzi's "Zhuangzi dreamed he was a butterfly", and the evil demon in René Descartes' Meditations on First Philosophy.

Recently, many contemporary philosophers believe that virtual reality will seriously affect human autonomy as a form of brain in a vat. But another view is that VR will not destroy our cognitive structure or take away our connection with reality. On the contrary, VR will allow us to have more new propositions, new insights and new perspectives to see the world.[5]

Philosophical debates[edit]

While the disembodied brain (the brain in a vat) can be seen as a helpful thought experiment, there are several philosophical debates surrounding the plausibility of the thought experiment. If these debates conclude that the thought experiment is implausible, a possible consequence would be that we are no closer to knowledge, truth, consciousness, representation, etc. than we were prior to the experiment.

Argument from biology[edit]

One argument against the BIV thought experiment derives from the idea that the BIV is not – and cannot be – biologically similar to that of an embodied brain (that is, a brain found in a person). Since the BIV is dis embodied, it follows that it does not have similar biology to that of an embodied brain. That is, the BIV lacks the connections from the body to the brain, which renders the BIV neither neuroanatomically nor neurophysiologically similar to that of an embodied brain.[6][7] If this is the case, we cannot say that it is even possible for the BIV to have similar experiences to the embodied brain, since the brains are not equal. However, it could be counter-argued that the hypothetical machine could be made to also replicate those types of inputs.

Argument from externalism[edit]

A second argument deals directly with the stimuli coming into the brain. This is often referred to as the account from externalism or ultra-externalism.[8] In the BIV, the brain receives stimuli from a machine. In an embodied brain, however, the brain receives the stimuli from the sensors found in the body (via touching, tasting, smelling, etc.) which receive their input from the external environment. This argument oftentimes leads to the conclusion that there is a difference between what the BIV is representing and what the embodied brain is representing. This debate has been hashed out, but remains unresolved, by several philosophers including Uriah Kriegel,[9] Colin McGinn,[10] and Robert D. Rupert,[11] and has ramifications for philosophy of mind discussions on (but not limited to) representation, consciousness, content, cognition, and embodied cognition.[12]

In fiction[edit]

A poster for the film The Brain That Wouldn't Die, 1962

See also[edit]


  1. ^ Harman, Gilbert 1973: Thought, Princeton/NJ, p.5.
  2. ^ Putnam, Hilary. "Brains in a Vat" (PDF). Retrieved 21 April 2015. Cite journal requires |journal= (help)
  3. ^ Klein, Peter (2 June 2015). "Skepticism". Stanford Encyclopedia of Philosophy. Retrieved 7 January 2017.
  4. ^ Bouwsma, O.K. (1949). "Descartes' Evil Genius" (PDF). The Philosophical Review. 58, No.2.: 149–151 – via JSTOR.
  5. ^ Cogburn, Jon; Silcox, Mark (2014). "Against Brain-in-a-Vatism: On the Value of Virtual Reality". Philosophy & Technology. 27 (4): 561–579. doi:10.1007/s13347-013-0137-4. ISSN 2210-5433.
  6. ^ Heylighen, Francis (2012). "A Brain in a Vat Cannot Break Out: Why the Singularity Must be Extended, Embedded, and Embodied". Journal of Consciousness Studies. 19 (1–2): 126–142.
  7. ^ Thompson, Evan; Cosmelli, Diego (Spring 2011). "Brain in a Vat or Body in a World? Brainbound versus Enactive Views of Experience". Philosophical Topics. 39 (1): 163–180. doi:10.5840/philtopics201139119. S2CID 170332029.
  8. ^ Kirk, Robert (1997). "Consciousness, Information and External Relations". Communication and Cognition. 30 (3–4).
  9. ^ Kriegel, Uriah (2014). Current Controversies in Philosophy of Mind. Routledge. pp. 180–95.
  10. ^ McGinn, Colin (1988). "Consciousness and Content". Proceedings of the British Academy. 76: 219–39.
  11. ^ Rupert, Robert (2014). The Sufficiency of Objective Representation. Current Controversies in Philosophy of Mind. Routledge. pp. 180–95.
  12. ^ Shapiro, Lawrence (2014). When Is Cognition Embodied. Current Controversies in Philosophy of Mind. Routledge. pp. 73–90.
  13. ^ "The Colossus of New York (1958)". MonsterHunter. 27 September 2013. Retrieved 11 March 2018. It turns out that Jeremy’s brain was sitting in a glass case of water hooked up to an EEG machine which led me to believe that they must have had some kind of clearance sale on set leftovers from Donovan’s Brain. (with photo).

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