William James’ squirrel:
SOME YEARS AGO, being with a camping party in the mountains, I returned from a solitary ramble to find every one engaged in a ferocious metaphysical dispute. The corpus of the dispute was a squirrel – a live squirrel supposed to be clinging to one side of a tree-trunk; while over against the tree’s opposite side a human being was imagined to stand. This human witness tries to get sight of the squirrel by moving rapidly round the tree, but no matter how fast he goes, the squirrel moves as fast in the opposite direction, and always keeps the tree between himself and the man, so that never a glimpse of him is caught. The resultant metaphysical problem now is this: Does the man go round the squirrel or not? He goes round the tree, sure enough, and the squirrel is on the tree; but does he go round the squirrel? [Stop for discussion] In the unlimited leisure of the wilderness, discussion had been worn threadbare. Every one had taken sides, and was obstinate; and the numbers on both sides were even. Each side, when I appeared therefore appealed to me to make it a majority. Mindful of the scholastic adage that whenever you meet a contradiction you must make a distinction, I immediately sought and found one, as follows: “Which party is right,” I said, “depends on what you practically mean by ‘going round’ the squirrel. If you mean passing from the north of him to the east, then to the south, then to the west, and then to the north of him again, obviously the man does go round him, for he occupies these successive positions. But if on the contrary you mean being first in front of him, then on the right of him, then behind him, then on his left, and finally in front again, it is quite as obvious that the man fails to go round him, for by the compensating movements the squirrel makes, he keeps his belly turned towards the man all the time, and his back turned away. Make the distinction, and there is no occasion for any farther dispute. You are both right and both wrong according as you conceive the verb ‘to go round’ in one practical fashion or the other.”
[“What is pragmatism?” 1904 lecture]
Descartes’ Evil Genius:
I shall then suppose, not that God who is supremely good and the fountain of truth, but some evil genius not less powerful than deceitful, has employed his whole energies in deceiving me; I shall consider that the heavens, the earth, colors, figures, sound, and all other external things are nothing but the illusions and dreams of which this genius has availed himself in order to lay traps for my credulity; I shall consider myself as having no hands, no eyes, no flesh, no blood, nor any senses, yet falsely believing myself to possess all these things; I shall remain obstinately attached to this idea, and if by this means it is not in my power to arrive at the knowledge of any truth, I may at least do what is in my power [i.e. suspend my judgment], and with firm purpose avoid giving credence to any false thing, or being imposed upon by this arch deceiver, however powerful and deceptive he may be. But this task is a laborious one, and insensibly a certain lassitude leads me into the course of my ordinary life. And just as a captive who in sleep enjoys an imaginary liberty, when he begins to suspect that his liberty is but a dream fears to awaken, and conspires with these agreeable illusions that the deception may be prolonged, so insensibly of my own accord I fall back into my former opinions, and I dread awakening from this slumber, lest the laborious wakefulness which would follow the tranquility of this repose should have to be spent not in daylight, but in the excessive darkness of the difficulties which have just been discussed.
I suppose, then, that all the things that I see are false; I persuade myself that nothing has ever existed of all that my fallacious memory represents to me. I consider that I possess no senses; I imagine that body, figure, extension, movement and place are but the fictions of my mind. What, then, can be esteemed as true? Perhaps nothing at all, unless that there is nothing in the world that is certain.
There is a village in which all the adult males are clean shaven. In the village is a barber. The barber shaves all and only those adult males who do not shave themselves. So, if Bob shaves himself then the barber does not shave Bob. And, if Bob does not shave himself then the barber does shave Bob.
Question: Does the barber shave himself?
Hypothesis: The world and everything in it was created five minutes ago.
Russell wants to show that the memories of something are logically independent of that something, but the hypothesis has been used to support skepticism.
Russell’s teapot, sometimes called the Celestial Teapot, was an analogy first coined by the philosopher Bertrand Russell, to refute the idea that the burden of proof lies somehow upon the sceptic to disprove the unfalsifiable claims of religion. In an article entitled Is There a God?, commissioned (but never published) by Illustrated magazine in 1952, Russell said the following:
If I were to suggest that between the Earth and Mars there is a china teapot revolving about the sun in an elliptical orbit, nobody would be able to disprove my assertion provided I were careful to add that the teapot is too small to be revealed even by our most powerful telescopes. But if I were to go on to say that, since my assertion cannot be disproved, it is intolerable presumption on the part of human reason to doubt it, I should rightly be thought to be talking nonsense. If, however, the existence of such a teapot were affirmed in ancient books, taught as the sacred truth every Sunday, and instilled into the minds of children at school, hesitation to believe in its existence would become a mark of eccentricity and entitle the doubter to the attentions of the psychiatrist in an enlightened age or of the Inquisitor in an earlier time.
In his book A Devil’s Chaplain, Richard Dawkins developed the teapot theme a little further:
The reason organized religion merits outright hostility is that, unlike belief in Russell’s teapot, religion is powerful, influential, tax-exempt and systematically passed on to children too young to defend themselves. Children are not compelled to spend their formative years memorizing loony books about teapots. Government-subsidized schools don’t exclude children whose parents prefer the wrong shape of teapot. Teapot-believers don’t stone teapot-unbelievers, teapot-apostates, teapot-heretics and teapot-blasphemers to death. Mothers don’t warn their sons off marrying teapot-shiksas whose parents believe in three teapots rather than one. People who put the milk in first don’t kneecap those who put the tea in first.
Similar concepts to Russell’s teapot are the Invisible Pink Unicorn, and Flying Spaghetti Monster.