Putnam's Brain in a Vat   2017  JPG  "Imagine that a human being [...] has been subjected to an operation by an evil scientist. The person’s brain [...] has been removed from the body and placed in a vat of nutrients which keeps the brain alive. The nerve endings have been connected to a super-scientific computer which causes the person whose brain it is to have the illusion that everything is perfectly normal. [...]. It can even seem to the victim that he is sitting and reading these very words about the amusing but quite absurd supposition that there is an evil scientist who removes people’s brains from their bodies and places them in a vat of nutrients which keep the brains alive." - Hilary Putnam,  Reason, Truth, and History,  1981

Putnam's Brain in a Vat

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"Imagine that a human being [...] has been subjected to an operation by an evil scientist. The person’s brain [...] has been removed from the body and placed in a vat of nutrients which keeps the brain alive. The nerve endings have been connected to a super-scientific computer which causes the person whose brain it is to have the illusion that everything is perfectly normal. [...]. It can even seem to the victim that he is sitting and reading these very words about the amusing but quite absurd supposition that there is an evil scientist who removes people’s brains from their bodies and places them in a vat of nutrients which keep the brains alive." - Hilary Putnam, Reason, Truth, and History, 1981

  Schrödinger's Cat   2017  JPG  "A cat is penned up in a steel chamber, along with the following device [...]: in a Geiger counter, there is a tiny bit of radioactive substance, so small, that perhaps in the course of the hour one of the atoms decays, but also, with equal probability, perhaps none; if it happens, the counter tube discharges and through a relay releases a hammer that shatters a small flask of hydrocyanic acid. If one has left this entire system to itself for an hour, one would say that the cat still lives if meanwhile no atom has decayed. The first atomic decay would have poisoned it. The psi-function of the entire system would express this by having in it the living and dead cat (pardon the expression) mixed or smeared out in equal parts." - Erwin Schrödinger, "The Present Situation in Quantum Mechanics", 1935

Schrödinger's Cat

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"A cat is penned up in a steel chamber, along with the following device [...]: in a Geiger counter, there is a tiny bit of radioactive substance, so small, that perhaps in the course of the hour one of the atoms decays, but also, with equal probability, perhaps none; if it happens, the counter tube discharges and through a relay releases a hammer that shatters a small flask of hydrocyanic acid. If one has left this entire system to itself for an hour, one would say that the cat still lives if meanwhile no atom has decayed. The first atomic decay would have poisoned it. The psi-function of the entire system would express this by having in it the living and dead cat (pardon the expression) mixed or smeared out in equal parts." - Erwin Schrödinger, "The Present Situation in Quantum Mechanics", 1935

  Nagel's Spider   2017  JPG  "One summer [...] a large spider appeared in the urinal of the men's room. [...] His life seemed miserable and exhausting. [...] So one day toward the end of the term I took a paper towel from the wall dispenser and extended it to him. His legs grasped the end of the towel and I lifted him out and deposited him on the tile floor. [...] The next day I found him in the same place, his legs shriveled in that way characteristic of dead spiders. His corpse stayed there for a week, until they finally swept the floor." - Thomas Nagel,  The View from Nowhere,  1986

Nagel's Spider

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"One summer [...] a large spider appeared in the urinal of the men's room. [...] His life seemed miserable and exhausting. [...] So one day toward the end of the term I took a paper towel from the wall dispenser and extended it to him. His legs grasped the end of the towel and I lifted him out and deposited him on the tile floor. [...] The next day I found him in the same place, his legs shriveled in that way characteristic of dead spiders. His corpse stayed there for a week, until they finally swept the floor." - Thomas Nagel, The View from Nowhere, 1986

  Galileo's Ship   2017  JPG  "Shut yourself up with some friend in the main cabin below decks on some large ship, and have with you there [...] a large bowl of water with some fish in it. [...] Observe carefully how [...] the fish swim indifferently in all directions. [...] The fish in their water will swim toward the front of their bowl with no more effort than toward the back, and will go with equal ease to bait placed anywhere around the edges of the bowl." - Galileo Galilei,  Dialogue Concerning the Two Chief World Systems , 1632

Galileo's Ship

2017

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"Shut yourself up with some friend in the main cabin below decks on some large ship, and have with you there [...] a large bowl of water with some fish in it. [...] Observe carefully how [...] the fish swim indifferently in all directions. [...] The fish in their water will swim toward the front of their bowl with no more effort than toward the back, and will go with equal ease to bait placed anywhere around the edges of the bowl." - Galileo Galilei, Dialogue Concerning the Two Chief World Systems, 1632

  Ross-Littlewood Paradox   2017  JPG  "Consider an experiment [with an infinitely large urn and infinite collection of balls]: At 1 minute to 12 P.M., balls numbered 1 through 10 are placed in the urn and ball number 10 is withdrawn [taking no time]. At 1/2 minute to 12 P.M., balls numbered 11 through 20 are placed in the urn and ball number 20 is withdrawn. At 1/4 minute to 12 P.M., balls numbered 21 through 30 are placed in the urn and ball number 30 is withdrawn, [...] and so on. [...] How many balls are in the urn at 12 P.M.? [...] An infinite number of balls [is] in the urn at 12 P.M., since any ball whose number is not of the form 10n, n > 1, will have been placed in the urn and [not] withdrawn before 12 P.M." - Sheldon Ross (expanding on ideas by John Littlewood from  Miscellany , 1953),  A First Course in Probability , 1976

Ross-Littlewood Paradox

2017

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"Consider an experiment [with an infinitely large urn and infinite collection of balls]: At 1 minute to 12 P.M., balls numbered 1 through 10 are placed in the urn and ball number 10 is withdrawn [taking no time]. At 1/2 minute to 12 P.M., balls numbered 11 through 20 are placed in the urn and ball number 20 is withdrawn. At 1/4 minute to 12 P.M., balls numbered 21 through 30 are placed in the urn and ball number 30 is withdrawn, [...] and so on. [...] How many balls are in the urn at 12 P.M.? [...] An infinite number of balls [is] in the urn at 12 P.M., since any ball whose number is not of the form 10n, n > 1, will have been placed in the urn and [not] withdrawn before 12 P.M." - Sheldon Ross (expanding on ideas by John Littlewood from Miscellany, 1953), A First Course in Probability, 1976

  Thomson's Transplant Problem   2017  JPG  “Imagine yourself to be a surgeon [...]. At the moment you have five patients who need organs. Two need one lung each, two need a kidney each, and the fifth needs a heart. If they do not get those organs today, they will all die [...]. The time is almost up when a report is brought to you that a young man who has just come into your clinic for his yearly check-up has exactly the right blood-type, and is in excellent health. Lo, you have a possible donor. All you need do is cut him up and distribute his parts among the five who need them. You ask, but he says, "Sorry. I deeply sympathize, but no." Would it be morally permissible for you to operate anyway?" - Judith Jarvis Thomson, "The Trolley Problem", 1985

Thomson's Transplant Problem

2017

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“Imagine yourself to be a surgeon [...]. At the moment you have five patients who need organs. Two need one lung each, two need a kidney each, and the fifth needs a heart. If they do not get those organs today, they will all die [...]. The time is almost up when a report is brought to you that a young man who has just come into your clinic for his yearly check-up has exactly the right blood-type, and is in excellent health. Lo, you have a possible donor. All you need do is cut him up and distribute his parts among the five who need them. You ask, but he says, "Sorry. I deeply sympathize, but no." Would it be morally permissible for you to operate anyway?" - Judith Jarvis Thomson, "The Trolley Problem", 1985

  Gettier Problem   2017  JPG  "Smith and Jones have applied for a certain job. And suppose that Smith has strong evidence for the following [...]: (d) Jones is the man who will get the job, and Jones has ten coins in his pocket. [...] Proposition (d) entails: (e) the man who will get the job has ten coins in his pocket. Let us suppose that Smith sees the entailment from (d) to (e), and accepts (e) on the grounds of (d), for which he has strong evidence. In this case, Smith is clearly justified in believing that (e) is true. But imagine, further, that unknown to Smith, he [...] will get the job. And, also, unknown to Smith, he [...] has ten coins in his pocket. Proposition (e) is then true, though proposition (d), from which Smith inferred (e), is false." - Edmund L. Gettier, "Is Justified True Belief Knowledge?", 1963

Gettier Problem

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"Smith and Jones have applied for a certain job. And suppose that Smith has strong evidence for the following [...]: (d) Jones is the man who will get the job, and Jones has ten coins in his pocket. [...] Proposition (d) entails: (e) the man who will get the job has ten coins in his pocket. Let us suppose that Smith sees the entailment from (d) to (e), and accepts (e) on the grounds of (d), for which he has strong evidence. In this case, Smith is clearly justified in believing that (e) is true. But imagine, further, that unknown to Smith, he [...] will get the job. And, also, unknown to Smith, he [...] has ten coins in his pocket. Proposition (e) is then true, though proposition (d), from which Smith inferred (e), is false." - Edmund L. Gettier, "Is Justified True Belief Knowledge?", 1963

  Wittgenstein's "S"   2017  JPG  "I want to keep a diary about the recurrence of a certain sensation. To this end I associate it with the sign "S" and write this sign in a calendar for every day on which I have the sensation. [...] I speak, or write the sign down, and at the same time I concentrate my attention on the sensation [...]. This process brings it about that I remember the connection right in the future. But in the present case I have no criterion for correctness.” - Ludwig Wittgenstein,  Philosophical Investigations , 1953

Wittgenstein's "S"

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"I want to keep a diary about the recurrence of a certain sensation. To this end I associate it with the sign "S" and write this sign in a calendar for every day on which I have the sensation. [...] I speak, or write the sign down, and at the same time I concentrate my attention on the sensation [...]. This process brings it about that I remember the connection right in the future. But in the present case I have no criterion for correctness.” - Ludwig Wittgenstein, Philosophical Investigations, 1953

  Diamond's Animals with Wheels   2017  JPG  "Why did evolution not anticipate the most important element of human transportation, the wheel? [...] Let us evaluate a [...] hypothetical wheeled animal" - Jared Diamond, "The Biology of the Wheel", 1983

Diamond's Animals with Wheels

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"Why did evolution not anticipate the most important element of human transportation, the wheel? [...] Let us evaluate a [...] hypothetical wheeled animal" - Jared Diamond, "The Biology of the Wheel", 1983

  Berkeley's Orange   2017  JPG  "George Bishop stared intently at the bowl of oranges before him [...]. He started by making an obvious distinction between the features of the oranges that are mere appearances and those properties that they really have. [...] But as he started stripping away the "mere appearances" from the fruits, he found himself left with vanishingly little. [...] To truly imagine the fruit in itself, independent of the mere appearances of sense perception, he was left with the vague idea of something, he knew not what. So what is the real fruit: this gossamer "something" or the collection of mere appearances after all?" - George Berkeley,  The Principles of Human Knowledge , 1710

Berkeley's Orange

2017

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"George Bishop stared intently at the bowl of oranges before him [...]. He started by making an obvious distinction between the features of the oranges that are mere appearances and those properties that they really have. [...] But as he started stripping away the "mere appearances" from the fruits, he found himself left with vanishingly little. [...] To truly imagine the fruit in itself, independent of the mere appearances of sense perception, he was left with the vague idea of something, he knew not what. So what is the real fruit: this gossamer "something" or the collection of mere appearances after all?" - George Berkeley, The Principles of Human Knowledge, 1710

  Polchinski's Paradox   2017  JPG  "In Polchinski's paradox, the billiard ball goes back in time and, by hitting itself, prevents itself from ever going back in time.." - Kip S. Thorne in his 1995 book,  Black Holes and Time Warps , describing a thought experiment originally created by Joseph Polchinski circa 1990.

Polchinski's Paradox

2017

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"In Polchinski's paradox, the billiard ball goes back in time and, by hitting itself, prevents itself from ever going back in time.." - Kip S. Thorne in his 1995 book, Black Holes and Time Warps, describing a thought experiment originally created by Joseph Polchinski circa 1990.

  Bernoulli's St. Petersburg Paradox   2017  JPG  "Peter tosses a coin and continues to do so until it should land "heads" when it comes to the ground. He agrees to give Paul one ducat if he gets "heads" on the very first throw, two ducats if he gets it on the second, four if on the third, eight if on the fourth, and so on, so that with each additional throw the number of ducats he must pay is doubled." - Daniel Bernoulli, "Exposition of a New Theory on the Measurement of Risk", 1738

Bernoulli's St. Petersburg Paradox

2017

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"Peter tosses a coin and continues to do so until it should land "heads" when it comes to the ground. He agrees to give Paul one ducat if he gets "heads" on the very first throw, two ducats if he gets it on the second, four if on the third, eight if on the fourth, and so on, so that with each additional throw the number of ducats he must pay is doubled." - Daniel Bernoulli, "Exposition of a New Theory on the Measurement of Risk", 1738

  Einstein's Mirror   2017  JPG  "It was the problem of what one would see in a mirror if both observer and mirror were moving at the speed of light that set Einstein on his path to relativity." - Anthony J. G. Hey and Patrick Walters in their 1997 book,  Einstein's Mirror , describing a thought experiment by Albert Einstein, who conceived the idea in 1895, at the age of sixteen.

Einstein's Mirror

2017

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"It was the problem of what one would see in a mirror if both observer and mirror were moving at the speed of light that set Einstein on his path to relativity." - Anthony J. G. Hey and Patrick Walters in their 1997 book, Einstein's Mirror, describing a thought experiment by Albert Einstein, who conceived the idea in 1895, at the age of sixteen.

  Galileo's Falling Objects   2017  JPG  "Who would ever believe [...] if from a high tower two stones, one stone twice the size of the other, were flung simultaneously, that when the smaller was halfway down the tower, the larger would have already reached the ground?" - Galileo Galilei,  On Motion , c. 1589-1592

Galileo's Falling Objects

2017

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"Who would ever believe [...] if from a high tower two stones, one stone twice the size of the other, were flung simultaneously, that when the smaller was halfway down the tower, the larger would have already reached the ground?" - Galileo Galilei, On Motion, c. 1589-1592

  Tucker's Prisoner's Dilemma   2017  JPG  "Two men, charged with a joint violation of law, are held separately by the police. Each is told that (1) if one confesses and the other does not, the former will be given a reward of one unit and the latter will be fined two units, (2) if both confess, each will be fined one unit. At the same time each has good reason to believe that (3) if neither confesses, both will go clear." - Albert Tucker, "A Two-Person Dilemma", 1950

Tucker's Prisoner's Dilemma

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"Two men, charged with a joint violation of law, are held separately by the police. Each is told that (1) if one confesses and the other does not, the former will be given a reward of one unit and the latter will be fined two units, (2) if both confess, each will be fined one unit. At the same time each has good reason to believe that (3) if neither confesses, both will go clear." - Albert Tucker, "A Two-Person Dilemma", 1950

  Stevin's Continuous Motion   2017  JPG  "Descent on the one and ascent on the other side will continue for ever, because the cause is always the same, and the spheres will automatically perform a perpetual motion." - Simon Stevin,  The Principles of the Art of Weighing , 1586

Stevin's Continuous Motion

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"Descent on the one and ascent on the other side will continue for ever, because the cause is always the same, and the spheres will automatically perform a perpetual motion." - Simon Stevin, The Principles of the Art of Weighing, 1586

  Chekhov's Gun   2017  JPG  "If in the first act you have hung a pistol on the wall, then in the following one it should be fired. Otherwise don't put it there." - Anton Chekhov, "Reminiscences of A. P. Chekhov", 1904

Chekhov's Gun

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"If in the first act you have hung a pistol on the wall, then in the following one it should be fired. Otherwise don't put it there." - Anton Chekhov, "Reminiscences of A. P. Chekhov", 1904

  Condillac's Statue   2017  JPG  "We imagined a statue internally organized like ourselves, and animated by a mind deprived of every kind of idea. We further supposed that its marble exterior did not allow it the use of any of its senses, and we reserved for ourselves the freedom to open them at will to the different impressions they are susceptible of." - Étienne Bonnot de Condillac,  A Treatise on the Sensations , 1754

Condillac's Statue

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"We imagined a statue internally organized like ourselves, and animated by a mind deprived of every kind of idea. We further supposed that its marble exterior did not allow it the use of any of its senses, and we reserved for ourselves the freedom to open them at will to the different impressions they are susceptible of." - Étienne Bonnot de Condillac, A Treatise on the Sensations, 1754

  Decartes' Demon   2017  JPG  "Some evil demon [...] 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 judgement. I shall consider myself as not having hands or eyes, or flesh, or blood or senses, but as falsely believing that I have all these things." - René Descartes,  Meditations on First Philosophy , 1641

Decartes' Demon

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"Some evil demon [...] 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 judgement. I shall consider myself as not having hands or eyes, or flesh, or blood or senses, but as falsely believing that I have all these things." - René Descartes, Meditations on First Philosophy, 1641

  Nietzsche's Demon   2017  JPG  “What, if some day or night a demon were to steal after you into your loneliest loneliness and say to you: 'This life as you now live it and have lived it, you will have to live once more and innumerable times more; and there will be nothing new in it, but every pain and every joy and every thought and sigh and everything unutterably small or great in your life will have to return to you, all in the same succession and sequence [...]. The eternal hourglass of existence is turned upside down again and again, and you with it, speck of dust!'" - Friedrich Nietzsche,  The Gay Science , 1882

Nietzsche's Demon

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“What, if some day or night a demon were to steal after you into your loneliest loneliness and say to you: 'This life as you now live it and have lived it, you will have to live once more and innumerable times more; and there will be nothing new in it, but every pain and every joy and every thought and sigh and everything unutterably small or great in your life will have to return to you, all in the same succession and sequence [...]. The eternal hourglass of existence is turned upside down again and again, and you with it, speck of dust!'" - Friedrich Nietzsche, The Gay Science, 1882

  Bostrom's Paperclip Maximizer   2017  JPG  "It also seems perfectly possible to have a superintelligence whose sole goal is something completely arbitrary, such as to manufacture as many paperclips as possible, and who would resist with all its might any attempt to alter this goal. [...] The consequence [could be] that it starts transforming first all of earth and then increasing portions of space into paperclip manufacturing facilities." - Nick Bostrom, "Ethical Issues in Advanced Artificial Intelligence", 2003

Bostrom's Paperclip Maximizer

2017

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"It also seems perfectly possible to have a superintelligence whose sole goal is something completely arbitrary, such as to manufacture as many paperclips as possible, and who would resist with all its might any attempt to alter this goal. [...] The consequence [could be] that it starts transforming first all of earth and then increasing portions of space into paperclip manufacturing facilities." - Nick Bostrom, "Ethical Issues in Advanced Artificial Intelligence", 2003

  Jackson's Mary   2017  JPG  "Mary is a brilliant scientist [...] forced to investigate the world from a black and white room via a black and white television monitor. She specializes in the neurophysiology of vision and acquires, let us suppose, all the physical information there is to obtain about what goes on when we see ripe tomatoes, or the sky, and use terms like "red", "blue", and so on. [...] What will happen when Mary is released from her black and white room [...]? Will she learn anything or not?" - Frank Jackson, "Epiphenomenal Qualia", 1982

Jackson's Mary

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"Mary is a brilliant scientist [...] forced to investigate the world from a black and white room via a black and white television monitor. She specializes in the neurophysiology of vision and acquires, let us suppose, all the physical information there is to obtain about what goes on when we see ripe tomatoes, or the sky, and use terms like "red", "blue", and so on. [...] What will happen when Mary is released from her black and white room [...]? Will she learn anything or not?" - Frank Jackson, "Epiphenomenal Qualia", 1982

  Jackson's Slug   2017  JPG  "Suppose we discovered living on the bottom of the deepest oceans a sort of sea slug which manifested intelligence. Perhaps survival in the conditions required rational powers. [...] They have developed sciences which work surprisingly well in these restricted terms. They also have philosophers, called slugists. [...] The tough-minded slugists hold that the restricted terms (or ones pretty like them which may be introduced as their sciences progress) suffice in principle to describe everything without remainder. [...] Their opponents, the soft-minded slugists [point out] that no slugist has ever succeeded in spelling out how this mysterious residue fits into the highly successful view that their sciences have and are developing of how their world works.” - Frank Jackson, "Epiphenomenal Qualia", 1982

Jackson's Slug

2017

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"Suppose we discovered living on the bottom of the deepest oceans a sort of sea slug which manifested intelligence. Perhaps survival in the conditions required rational powers. [...] They have developed sciences which work surprisingly well in these restricted terms. They also have philosophers, called slugists. [...] The tough-minded slugists hold that the restricted terms (or ones pretty like them which may be introduced as their sciences progress) suffice in principle to describe everything without remainder. [...] Their opponents, the soft-minded slugists [point out] that no slugist has ever succeeded in spelling out how this mysterious residue fits into the highly successful view that their sciences have and are developing of how their world works.” - Frank Jackson, "Epiphenomenal Qualia", 1982

  Foot's Trolley Problem   2017  JPG  "[Suppose] that [the] driver of a runaway tram [...] can only steer from one narrow track on to another; five men are working on one track and one man on the other; anyone on the track he enters is bound to be killed." - Philippa Foot, "The Problem of Abortion and the Doctrine of the Double Effect", 1967

Foot's Trolley Problem

2017

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"[Suppose] that [the] driver of a runaway tram [...] can only steer from one narrow track on to another; five men are working on one track and one man on the other; anyone on the track he enters is bound to be killed." - Philippa Foot, "The Problem of Abortion and the Doctrine of the Double Effect", 1967

  Putnam's Brain in a Vat   2017  JPG  "Imagine that a human being [...] has been subjected to an operation by an evil scientist. The person’s brain [...] has been removed from the body and placed in a vat of nutrients which keeps the brain alive. The nerve endings have been connected to a super-scientific computer which causes the person whose brain it is to have the illusion that everything is perfectly normal. [...]. It can even seem to the victim that he is sitting and reading these very words about the amusing but quite absurd supposition that there is an evil scientist who removes people’s brains from their bodies and places them in a vat of nutrients which keep the brains alive." - Hilary Putnam,  Reason, Truth, and History,  1981
  Schrödinger's Cat   2017  JPG  "A cat is penned up in a steel chamber, along with the following device [...]: in a Geiger counter, there is a tiny bit of radioactive substance, so small, that perhaps in the course of the hour one of the atoms decays, but also, with equal probability, perhaps none; if it happens, the counter tube discharges and through a relay releases a hammer that shatters a small flask of hydrocyanic acid. If one has left this entire system to itself for an hour, one would say that the cat still lives if meanwhile no atom has decayed. The first atomic decay would have poisoned it. The psi-function of the entire system would express this by having in it the living and dead cat (pardon the expression) mixed or smeared out in equal parts." - Erwin Schrödinger, "The Present Situation in Quantum Mechanics", 1935
  Nagel's Spider   2017  JPG  "One summer [...] a large spider appeared in the urinal of the men's room. [...] His life seemed miserable and exhausting. [...] So one day toward the end of the term I took a paper towel from the wall dispenser and extended it to him. His legs grasped the end of the towel and I lifted him out and deposited him on the tile floor. [...] The next day I found him in the same place, his legs shriveled in that way characteristic of dead spiders. His corpse stayed there for a week, until they finally swept the floor." - Thomas Nagel,  The View from Nowhere,  1986
  Galileo's Ship   2017  JPG  "Shut yourself up with some friend in the main cabin below decks on some large ship, and have with you there [...] a large bowl of water with some fish in it. [...] Observe carefully how [...] the fish swim indifferently in all directions. [...] The fish in their water will swim toward the front of their bowl with no more effort than toward the back, and will go with equal ease to bait placed anywhere around the edges of the bowl." - Galileo Galilei,  Dialogue Concerning the Two Chief World Systems , 1632
  Ross-Littlewood Paradox   2017  JPG  "Consider an experiment [with an infinitely large urn and infinite collection of balls]: At 1 minute to 12 P.M., balls numbered 1 through 10 are placed in the urn and ball number 10 is withdrawn [taking no time]. At 1/2 minute to 12 P.M., balls numbered 11 through 20 are placed in the urn and ball number 20 is withdrawn. At 1/4 minute to 12 P.M., balls numbered 21 through 30 are placed in the urn and ball number 30 is withdrawn, [...] and so on. [...] How many balls are in the urn at 12 P.M.? [...] An infinite number of balls [is] in the urn at 12 P.M., since any ball whose number is not of the form 10n, n > 1, will have been placed in the urn and [not] withdrawn before 12 P.M." - Sheldon Ross (expanding on ideas by John Littlewood from  Miscellany , 1953),  A First Course in Probability , 1976
  Thomson's Transplant Problem   2017  JPG  “Imagine yourself to be a surgeon [...]. At the moment you have five patients who need organs. Two need one lung each, two need a kidney each, and the fifth needs a heart. If they do not get those organs today, they will all die [...]. The time is almost up when a report is brought to you that a young man who has just come into your clinic for his yearly check-up has exactly the right blood-type, and is in excellent health. Lo, you have a possible donor. All you need do is cut him up and distribute his parts among the five who need them. You ask, but he says, "Sorry. I deeply sympathize, but no." Would it be morally permissible for you to operate anyway?" - Judith Jarvis Thomson, "The Trolley Problem", 1985
  Gettier Problem   2017  JPG  "Smith and Jones have applied for a certain job. And suppose that Smith has strong evidence for the following [...]: (d) Jones is the man who will get the job, and Jones has ten coins in his pocket. [...] Proposition (d) entails: (e) the man who will get the job has ten coins in his pocket. Let us suppose that Smith sees the entailment from (d) to (e), and accepts (e) on the grounds of (d), for which he has strong evidence. In this case, Smith is clearly justified in believing that (e) is true. But imagine, further, that unknown to Smith, he [...] will get the job. And, also, unknown to Smith, he [...] has ten coins in his pocket. Proposition (e) is then true, though proposition (d), from which Smith inferred (e), is false." - Edmund L. Gettier, "Is Justified True Belief Knowledge?", 1963
  Wittgenstein's "S"   2017  JPG  "I want to keep a diary about the recurrence of a certain sensation. To this end I associate it with the sign "S" and write this sign in a calendar for every day on which I have the sensation. [...] I speak, or write the sign down, and at the same time I concentrate my attention on the sensation [...]. This process brings it about that I remember the connection right in the future. But in the present case I have no criterion for correctness.” - Ludwig Wittgenstein,  Philosophical Investigations , 1953
  Diamond's Animals with Wheels   2017  JPG  "Why did evolution not anticipate the most important element of human transportation, the wheel? [...] Let us evaluate a [...] hypothetical wheeled animal" - Jared Diamond, "The Biology of the Wheel", 1983
  Berkeley's Orange   2017  JPG  "George Bishop stared intently at the bowl of oranges before him [...]. He started by making an obvious distinction between the features of the oranges that are mere appearances and those properties that they really have. [...] But as he started stripping away the "mere appearances" from the fruits, he found himself left with vanishingly little. [...] To truly imagine the fruit in itself, independent of the mere appearances of sense perception, he was left with the vague idea of something, he knew not what. So what is the real fruit: this gossamer "something" or the collection of mere appearances after all?" - George Berkeley,  The Principles of Human Knowledge , 1710
  Polchinski's Paradox   2017  JPG  "In Polchinski's paradox, the billiard ball goes back in time and, by hitting itself, prevents itself from ever going back in time.." - Kip S. Thorne in his 1995 book,  Black Holes and Time Warps , describing a thought experiment originally created by Joseph Polchinski circa 1990.
  Bernoulli's St. Petersburg Paradox   2017  JPG  "Peter tosses a coin and continues to do so until it should land "heads" when it comes to the ground. He agrees to give Paul one ducat if he gets "heads" on the very first throw, two ducats if he gets it on the second, four if on the third, eight if on the fourth, and so on, so that with each additional throw the number of ducats he must pay is doubled." - Daniel Bernoulli, "Exposition of a New Theory on the Measurement of Risk", 1738
  Einstein's Mirror   2017  JPG  "It was the problem of what one would see in a mirror if both observer and mirror were moving at the speed of light that set Einstein on his path to relativity." - Anthony J. G. Hey and Patrick Walters in their 1997 book,  Einstein's Mirror , describing a thought experiment by Albert Einstein, who conceived the idea in 1895, at the age of sixteen.
  Galileo's Falling Objects   2017  JPG  "Who would ever believe [...] if from a high tower two stones, one stone twice the size of the other, were flung simultaneously, that when the smaller was halfway down the tower, the larger would have already reached the ground?" - Galileo Galilei,  On Motion , c. 1589-1592
  Tucker's Prisoner's Dilemma   2017  JPG  "Two men, charged with a joint violation of law, are held separately by the police. Each is told that (1) if one confesses and the other does not, the former will be given a reward of one unit and the latter will be fined two units, (2) if both confess, each will be fined one unit. At the same time each has good reason to believe that (3) if neither confesses, both will go clear." - Albert Tucker, "A Two-Person Dilemma", 1950
  Stevin's Continuous Motion   2017  JPG  "Descent on the one and ascent on the other side will continue for ever, because the cause is always the same, and the spheres will automatically perform a perpetual motion." - Simon Stevin,  The Principles of the Art of Weighing , 1586
  Chekhov's Gun   2017  JPG  "If in the first act you have hung a pistol on the wall, then in the following one it should be fired. Otherwise don't put it there." - Anton Chekhov, "Reminiscences of A. P. Chekhov", 1904
  Condillac's Statue   2017  JPG  "We imagined a statue internally organized like ourselves, and animated by a mind deprived of every kind of idea. We further supposed that its marble exterior did not allow it the use of any of its senses, and we reserved for ourselves the freedom to open them at will to the different impressions they are susceptible of." - Étienne Bonnot de Condillac,  A Treatise on the Sensations , 1754
  Decartes' Demon   2017  JPG  "Some evil demon [...] 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 judgement. I shall consider myself as not having hands or eyes, or flesh, or blood or senses, but as falsely believing that I have all these things." - René Descartes,  Meditations on First Philosophy , 1641
  Nietzsche's Demon   2017  JPG  “What, if some day or night a demon were to steal after you into your loneliest loneliness and say to you: 'This life as you now live it and have lived it, you will have to live once more and innumerable times more; and there will be nothing new in it, but every pain and every joy and every thought and sigh and everything unutterably small or great in your life will have to return to you, all in the same succession and sequence [...]. The eternal hourglass of existence is turned upside down again and again, and you with it, speck of dust!'" - Friedrich Nietzsche,  The Gay Science , 1882
  Bostrom's Paperclip Maximizer   2017  JPG  "It also seems perfectly possible to have a superintelligence whose sole goal is something completely arbitrary, such as to manufacture as many paperclips as possible, and who would resist with all its might any attempt to alter this goal. [...] The consequence [could be] that it starts transforming first all of earth and then increasing portions of space into paperclip manufacturing facilities." - Nick Bostrom, "Ethical Issues in Advanced Artificial Intelligence", 2003
  Jackson's Mary   2017  JPG  "Mary is a brilliant scientist [...] forced to investigate the world from a black and white room via a black and white television monitor. She specializes in the neurophysiology of vision and acquires, let us suppose, all the physical information there is to obtain about what goes on when we see ripe tomatoes, or the sky, and use terms like "red", "blue", and so on. [...] What will happen when Mary is released from her black and white room [...]? Will she learn anything or not?" - Frank Jackson, "Epiphenomenal Qualia", 1982
  Jackson's Slug   2017  JPG  "Suppose we discovered living on the bottom of the deepest oceans a sort of sea slug which manifested intelligence. Perhaps survival in the conditions required rational powers. [...] They have developed sciences which work surprisingly well in these restricted terms. They also have philosophers, called slugists. [...] The tough-minded slugists hold that the restricted terms (or ones pretty like them which may be introduced as their sciences progress) suffice in principle to describe everything without remainder. [...] Their opponents, the soft-minded slugists [point out] that no slugist has ever succeeded in spelling out how this mysterious residue fits into the highly successful view that their sciences have and are developing of how their world works.” - Frank Jackson, "Epiphenomenal Qualia", 1982
  Foot's Trolley Problem   2017  JPG  "[Suppose] that [the] driver of a runaway tram [...] can only steer from one narrow track on to another; five men are working on one track and one man on the other; anyone on the track he enters is bound to be killed." - Philippa Foot, "The Problem of Abortion and the Doctrine of the Double Effect", 1967

Putnam's Brain in a Vat

2017

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"Imagine that a human being [...] has been subjected to an operation by an evil scientist. The person’s brain [...] has been removed from the body and placed in a vat of nutrients which keeps the brain alive. The nerve endings have been connected to a super-scientific computer which causes the person whose brain it is to have the illusion that everything is perfectly normal. [...]. It can even seem to the victim that he is sitting and reading these very words about the amusing but quite absurd supposition that there is an evil scientist who removes people’s brains from their bodies and places them in a vat of nutrients which keep the brains alive." - Hilary Putnam, Reason, Truth, and History, 1981

Schrödinger's Cat

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"A cat is penned up in a steel chamber, along with the following device [...]: in a Geiger counter, there is a tiny bit of radioactive substance, so small, that perhaps in the course of the hour one of the atoms decays, but also, with equal probability, perhaps none; if it happens, the counter tube discharges and through a relay releases a hammer that shatters a small flask of hydrocyanic acid. If one has left this entire system to itself for an hour, one would say that the cat still lives if meanwhile no atom has decayed. The first atomic decay would have poisoned it. The psi-function of the entire system would express this by having in it the living and dead cat (pardon the expression) mixed or smeared out in equal parts." - Erwin Schrödinger, "The Present Situation in Quantum Mechanics", 1935

Nagel's Spider

2017

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"One summer [...] a large spider appeared in the urinal of the men's room. [...] His life seemed miserable and exhausting. [...] So one day toward the end of the term I took a paper towel from the wall dispenser and extended it to him. His legs grasped the end of the towel and I lifted him out and deposited him on the tile floor. [...] The next day I found him in the same place, his legs shriveled in that way characteristic of dead spiders. His corpse stayed there for a week, until they finally swept the floor." - Thomas Nagel, The View from Nowhere, 1986

Galileo's Ship

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"Shut yourself up with some friend in the main cabin below decks on some large ship, and have with you there [...] a large bowl of water with some fish in it. [...] Observe carefully how [...] the fish swim indifferently in all directions. [...] The fish in their water will swim toward the front of their bowl with no more effort than toward the back, and will go with equal ease to bait placed anywhere around the edges of the bowl." - Galileo Galilei, Dialogue Concerning the Two Chief World Systems, 1632

Ross-Littlewood Paradox

2017

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"Consider an experiment [with an infinitely large urn and infinite collection of balls]: At 1 minute to 12 P.M., balls numbered 1 through 10 are placed in the urn and ball number 10 is withdrawn [taking no time]. At 1/2 minute to 12 P.M., balls numbered 11 through 20 are placed in the urn and ball number 20 is withdrawn. At 1/4 minute to 12 P.M., balls numbered 21 through 30 are placed in the urn and ball number 30 is withdrawn, [...] and so on. [...] How many balls are in the urn at 12 P.M.? [...] An infinite number of balls [is] in the urn at 12 P.M., since any ball whose number is not of the form 10n, n > 1, will have been placed in the urn and [not] withdrawn before 12 P.M." - Sheldon Ross (expanding on ideas by John Littlewood from Miscellany, 1953), A First Course in Probability, 1976

Thomson's Transplant Problem

2017

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“Imagine yourself to be a surgeon [...]. At the moment you have five patients who need organs. Two need one lung each, two need a kidney each, and the fifth needs a heart. If they do not get those organs today, they will all die [...]. The time is almost up when a report is brought to you that a young man who has just come into your clinic for his yearly check-up has exactly the right blood-type, and is in excellent health. Lo, you have a possible donor. All you need do is cut him up and distribute his parts among the five who need them. You ask, but he says, "Sorry. I deeply sympathize, but no." Would it be morally permissible for you to operate anyway?" - Judith Jarvis Thomson, "The Trolley Problem", 1985

Gettier Problem

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"Smith and Jones have applied for a certain job. And suppose that Smith has strong evidence for the following [...]: (d) Jones is the man who will get the job, and Jones has ten coins in his pocket. [...] Proposition (d) entails: (e) the man who will get the job has ten coins in his pocket. Let us suppose that Smith sees the entailment from (d) to (e), and accepts (e) on the grounds of (d), for which he has strong evidence. In this case, Smith is clearly justified in believing that (e) is true. But imagine, further, that unknown to Smith, he [...] will get the job. And, also, unknown to Smith, he [...] has ten coins in his pocket. Proposition (e) is then true, though proposition (d), from which Smith inferred (e), is false." - Edmund L. Gettier, "Is Justified True Belief Knowledge?", 1963

Wittgenstein's "S"

2017

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"I want to keep a diary about the recurrence of a certain sensation. To this end I associate it with the sign "S" and write this sign in a calendar for every day on which I have the sensation. [...] I speak, or write the sign down, and at the same time I concentrate my attention on the sensation [...]. This process brings it about that I remember the connection right in the future. But in the present case I have no criterion for correctness.” - Ludwig Wittgenstein, Philosophical Investigations, 1953

Diamond's Animals with Wheels

2017

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"Why did evolution not anticipate the most important element of human transportation, the wheel? [...] Let us evaluate a [...] hypothetical wheeled animal" - Jared Diamond, "The Biology of the Wheel", 1983

Berkeley's Orange

2017

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"George Bishop stared intently at the bowl of oranges before him [...]. He started by making an obvious distinction between the features of the oranges that are mere appearances and those properties that they really have. [...] But as he started stripping away the "mere appearances" from the fruits, he found himself left with vanishingly little. [...] To truly imagine the fruit in itself, independent of the mere appearances of sense perception, he was left with the vague idea of something, he knew not what. So what is the real fruit: this gossamer "something" or the collection of mere appearances after all?" - George Berkeley, The Principles of Human Knowledge, 1710

Polchinski's Paradox

2017

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"In Polchinski's paradox, the billiard ball goes back in time and, by hitting itself, prevents itself from ever going back in time.." - Kip S. Thorne in his 1995 book, Black Holes and Time Warps, describing a thought experiment originally created by Joseph Polchinski circa 1990.

Bernoulli's St. Petersburg Paradox

2017

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"Peter tosses a coin and continues to do so until it should land "heads" when it comes to the ground. He agrees to give Paul one ducat if he gets "heads" on the very first throw, two ducats if he gets it on the second, four if on the third, eight if on the fourth, and so on, so that with each additional throw the number of ducats he must pay is doubled." - Daniel Bernoulli, "Exposition of a New Theory on the Measurement of Risk", 1738

Einstein's Mirror

2017

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"It was the problem of what one would see in a mirror if both observer and mirror were moving at the speed of light that set Einstein on his path to relativity." - Anthony J. G. Hey and Patrick Walters in their 1997 book, Einstein's Mirror, describing a thought experiment by Albert Einstein, who conceived the idea in 1895, at the age of sixteen.

Galileo's Falling Objects

2017

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"Who would ever believe [...] if from a high tower two stones, one stone twice the size of the other, were flung simultaneously, that when the smaller was halfway down the tower, the larger would have already reached the ground?" - Galileo Galilei, On Motion, c. 1589-1592

Tucker's Prisoner's Dilemma

2017

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"Two men, charged with a joint violation of law, are held separately by the police. Each is told that (1) if one confesses and the other does not, the former will be given a reward of one unit and the latter will be fined two units, (2) if both confess, each will be fined one unit. At the same time each has good reason to believe that (3) if neither confesses, both will go clear." - Albert Tucker, "A Two-Person Dilemma", 1950

Stevin's Continuous Motion

2017

JPG

"Descent on the one and ascent on the other side will continue for ever, because the cause is always the same, and the spheres will automatically perform a perpetual motion." - Simon Stevin, The Principles of the Art of Weighing, 1586

Chekhov's Gun

2017

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"If in the first act you have hung a pistol on the wall, then in the following one it should be fired. Otherwise don't put it there." - Anton Chekhov, "Reminiscences of A. P. Chekhov", 1904

Condillac's Statue

2017

JPG

"We imagined a statue internally organized like ourselves, and animated by a mind deprived of every kind of idea. We further supposed that its marble exterior did not allow it the use of any of its senses, and we reserved for ourselves the freedom to open them at will to the different impressions they are susceptible of." - Étienne Bonnot de Condillac, A Treatise on the Sensations, 1754

Decartes' Demon

2017

JPG

"Some evil demon [...] 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 judgement. I shall consider myself as not having hands or eyes, or flesh, or blood or senses, but as falsely believing that I have all these things." - René Descartes, Meditations on First Philosophy, 1641

Nietzsche's Demon

2017

JPG

“What, if some day or night a demon were to steal after you into your loneliest loneliness and say to you: 'This life as you now live it and have lived it, you will have to live once more and innumerable times more; and there will be nothing new in it, but every pain and every joy and every thought and sigh and everything unutterably small or great in your life will have to return to you, all in the same succession and sequence [...]. The eternal hourglass of existence is turned upside down again and again, and you with it, speck of dust!'" - Friedrich Nietzsche, The Gay Science, 1882

Bostrom's Paperclip Maximizer

2017

JPG

"It also seems perfectly possible to have a superintelligence whose sole goal is something completely arbitrary, such as to manufacture as many paperclips as possible, and who would resist with all its might any attempt to alter this goal. [...] The consequence [could be] that it starts transforming first all of earth and then increasing portions of space into paperclip manufacturing facilities." - Nick Bostrom, "Ethical Issues in Advanced Artificial Intelligence", 2003

Jackson's Mary

2017

JPG

"Mary is a brilliant scientist [...] forced to investigate the world from a black and white room via a black and white television monitor. She specializes in the neurophysiology of vision and acquires, let us suppose, all the physical information there is to obtain about what goes on when we see ripe tomatoes, or the sky, and use terms like "red", "blue", and so on. [...] What will happen when Mary is released from her black and white room [...]? Will she learn anything or not?" - Frank Jackson, "Epiphenomenal Qualia", 1982

Jackson's Slug

2017

JPG

"Suppose we discovered living on the bottom of the deepest oceans a sort of sea slug which manifested intelligence. Perhaps survival in the conditions required rational powers. [...] They have developed sciences which work surprisingly well in these restricted terms. They also have philosophers, called slugists. [...] The tough-minded slugists hold that the restricted terms (or ones pretty like them which may be introduced as their sciences progress) suffice in principle to describe everything without remainder. [...] Their opponents, the soft-minded slugists [point out] that no slugist has ever succeeded in spelling out how this mysterious residue fits into the highly successful view that their sciences have and are developing of how their world works.” - Frank Jackson, "Epiphenomenal Qualia", 1982

Foot's Trolley Problem

2017

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"[Suppose] that [the] driver of a runaway tram [...] can only steer from one narrow track on to another; five men are working on one track and one man on the other; anyone on the track he enters is bound to be killed." - Philippa Foot, "The Problem of Abortion and the Doctrine of the Double Effect", 1967

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