Paradox
's self-flowing flask fills itself in this diagram, but
perpetual motion machines don't exist.]]
A
paradox is an apparently
true statement that seems to lead to an
illogical contradiction, or to a situation that contradicts common intuition. Put simply, a paradox is 'the opposite of what one thinks to be true.' The identification of a paradox based on seemingly simple and reasonable concepts has often led to significant advances in
science,
philosophy and
mathematics.
The
etymology of paradox can be traced back to texts appearing at the dawn of the
renaissance, a period of accelerated scientific thought in Europe and Asia sometime after the year
1500 AD. The first forms of the word appeared as the late
Latin word
paradoxum, but is also found in
Greek texts as
paradoxon (however, Latin is predominantly derived from the
Greek alphabet--furthermore, English is derived from Roman Latin, but with the addition of the letters "J", "U" and "W"). The word is composed of the prefix
para- which means "contrary to", "altered" or "opposite of", and conjoined with the noun suffix
doxa, meaning "opinion." Compare
orthodox and
heterodox.
In
moral philosophy, paradox plays a particularly central role in debates on
ethics. For instance, an ethical admonition to "love thy neighbor" is not just in contrast with, but in contradiction to an armed neighbor actively trying to kill you: if he or she succeeds, then, you will not be able to love them. But to preemptively attack them or restrain them is not usually understood as very loving. This might be termed an
ethical dilemma. Another example is the conflict between an injunction not to steal and one to care for a family that you cannot afford to feed without stolen money.
It should be noted that many paradoxes rely on an essential assumption: that language (be it spoken, visual, or mathematic) accurately models the reality it is describing. In
quantum physics, many paradoxical behaviors can be observed (the
Heisenberg uncertainty principle, for instance) and some have attributed these paradoxes to inherent limitations of language and scientific models.
Alfred Korzybski, who founded the study of General Semantics, sums up this concept quite simply by having stated that, "The map is not the territory." A common example of the limitations of language are the forms of the word "to be." "Being" is not clearly defined (the area of philosophical study called
ontology has yet to produce a concrete meaning) and thus if a statement includes being as an essential element, it may be subject to paradox.
Types of paradoxes
Common themes in paradoxes include direct and indirect self-reference, infinity, circular definitions, and confusion of levels of reasoning.
Not all paradoxes are equal. For example, the Birthday paradox is more of a surprise than a paradox, while the resolution of Curry's paradox is still a matter of contention.
W. V. Quine (1962) distinguished three classes of paradox:\n* A veridical paradox produces a result that appears absurd but is demonstrated to be true nevertheless. Thus, the paradox of Frederic's birthday in The Pirates of Penzance establishes the surprising fact that a person may be more than N years old on his Nth birthday. Likewise, Arrow's impossibility theorem involves behavior of voting systems that is surprising but all too true.\n* A falsidical paradox establishes a result that not only appears false but actually is false; there is a fallacy in the supposed demonstration. The various invalid proofs (e.g. that 1 = 2) are classic examples, generally relying on a hidden division by zero. Another example would be the Horse paradox.\n* A paradox which is in neither class may be an antinomy, which reaches a self-contradictory result by properly applying accepted ways of reasoning. For example, the Grelling-Nelson paradox points out genuine problems in our understanding of the ideas of truth and description.1
List of paradoxes
Not all paradoxes fit neatly into one category. Some paradoxes include:
Veridical paradoxes
These are unintuitive results of correct logical reasoning.
: which door do you choose?]]
Mathematical/Logical
- Paradox of entailment: Inconsistent premises always make an argument valid. \n* Apportionment paradox: Some systems of apportioning representation can have unintuitive results\n** Alabama paradox\n** New states paradox\n** Population paradox\n* Averaging - the mathematical concept of an average, whether defined as the mean or median, leads to apparently paradoxical results - for example, it is possible that moving an entry from Wikipedia to Wiktionary would increase the average entry length on both sites - Will Rogers phenomenon\n* Arrow's paradox/Voting paradox/Condorcet paradox: You can't have all the attributes of an ideal voting system at once\n* Banach-Tarski paradox: Cut a ball into 5 pieces, re-assemble the pieces to get two balls, both of equal size to the first.\n* Birthday paradox: What is the chance that two people in a room have the same birthday?\n* Borel's paradox: Conditional probability density functions are not invariant under coordinate transformations.\n* Burali-Forti paradox: If the ordinal numbers formed a set, it would be an ordinal number which is smaller than itself.\n* Elevator paradox: Elevators can seem to be mostly going in one direction, as if they were being manufactured on the roof, and disassembled in the basement.\n* Galileo's paradox: Though most numbers are not squares, there are no more numbers than squares.\n* Gabriel's Horn or Torricelli's trumpet: A simple object with finite volume but infinite surface area. Also, the Mandelbrot set and various other fractals have finite area, but infinite perimeter. \n* Hausdorff paradox: There exists a countable subset C of the sphere S such that S\\C is equidecomposable with two copies of itself. \n* Hilbert's paradox of the Grand Hotel: If a hotel with infinitely many rooms is full, it can still take in more guests.\n* Monty Hall problem: An unintuitive consequence of conditional probability.\n* Monty Hell problem: Positive daily profits yield zero assets in the limit.\n* Raven paradox (or Hempel's Ravens): Observing a red apple increases the likelihood of all ravens being black.\n* Richard's paradox: A complete list of definitions of real numbers doesn't exist.\n* Simpson's paradox: An association in sub-populations may be reversed in the population. It appears that two sets of data separately support a certain hypothesis, but, when considered together, they support the opposite hypothesis.\n* Sleeping beauty paradox: One half or one third? news://rec.puzzles cannot agree on a probability.\n* Statistical paradox: It is quite possible to draw wrong conclusions from correlation. For example, towns with a larger number of churches generally have a higher crime rate - because both result from higher population. A professional organization once found that economists with a PhD actually had a lower average salary than those with a BS - but this was found to be due to the fact that those with a PhD worked in academia, where salaries are generally lower.
Psychological/Philosophical
- Abilene paradox: People take actions in contradiction to what they really want to do, and therefore defeat the very purposes of what they were trying to accomplish.\n* Buridan's ass: How can a rational choice be made between two outcomes of equal value?\n* Control paradox: Man can never be free of control, for to be free of control is to be controlled by oneself.\n* Paradox of hedonism: When one pursues happiness itself, one is miserable; but, when one pursues something else, one achieves happiness.\n* Epicurean paradox: The existence of evil is incompatible with the existence of an omnipotent and caring God.
Physical
Falsidical paradoxes
These are incorrect results of subtly false reasoning.\n* Epimenides paradox: A Cretan says "All Cretans are liars". (But see also the Liar paradox, an antinomy.)\n* Horse paradox: All horses are the same color.\n* Unexpected hanging paradox: The day of the hanging will be a surprise, so it can't happen at all, so it will be a surprise. (Similar to the Liar paradox, an antinomy.) \n* Zeno's paradoxes: When you reach the turtle's spot, it has already advanced a bit, so you can never catch it.
Antinomies
Paradoxes that show flaws in accepted reasoning, axioms, or definitions. Note that many of these are special cases, or adaptations, of Russell's paradox. \n* Barber paradox: The barber who shaves all men who don't shave themselves, and no-one else.\n* Berry paradox: What is "The first number not nameable in under ten words"? \n* Curry's paradox: "If I'm not mistaken, the world will end in a week."\n* Grelling-Nelson paradox: Is the word "heterological", meaning "not applicable to itself," a heterological word?\n* Liar paradox: "This sentence is false."\n* Quine's liar paradox: "Yields a falsehood when appended to its own quotation."\n* Russell's paradox: Is there a set of all those sets that do not contain themselves?
Antinomies of definition
These paradoxes rest simply on an ambiguous definition.\n* Ship of Theseus/George Washington's axe: When every component of the ship has been replaced at least once, is it still the same ship?\n* Sorites paradox: At what point does a heap stop being a heap as I take away grains of sand?\n* Richard's paradox
Conditional paradoxes
These are paradoxes only if certain special assumptions are made. \nSome of these show that those assumptions are false or incomplete, others are other types of paradoxes.\n* Fermi paradox: If there are many other sentient species in the Universe, then where are they? Shouldn't their presence be obvious?\n* Grandfather paradox: You travel back in time and kill your grandfather before he meets your grandmother which precludes your own conception.\n* The GZK paradox: high-energy cosmic rays have been observed which seem to violate the Greisen-Zatsepin-Kuzmin limit which is a consequence of special relativity \n* Jevons paradox: In economics, increases in efficiency lead to even larger increases in demand.\n* Mere addition paradox: is a large population living barely tolerable lives better than a small happy population?\n* Newcomb's paradox: How do you play a game against an omniscient opponent?\n* Nihilist paradox: if truth does not exist, the statement "truth does not exist" is a truth, thereby proving itself incorrect.\n* Olbers' paradox: If the universe is infinite, with infinitely many luminous stars uniformly distributed, the sky should be entirely bright because there's a star in every direction.\n* Omnipotence paradox: Can an omnipotent being create a rock too heavy to lift? Can an irresistible force move an unmovable object?\n* Predestination paradox: A man travels back in time and impregnates his great-great-grandmother. The result is a line of offspring and descendants, including the man's parent(s) and the man himself. Therefore, unless he makes the time-travel trip at all, he will never exist.\n* St. Petersburg paradox: People will only offer a modest fee for a reward of infinite value.
Other paradoxes
- Giffen paradox: Can increasing the price of bread make poor people eat more of it?\n* Kavka's toxin puzzle: Can one intend to drink the nondeadly toxin, if the intention is the only thing needed to get the reward?\n* Moore's paradox: "It's raining but I don't believe that it is."\n* Low birth weight paradox: Low birth weight babies have a higher mortality rate, babies of smoking mothers have lower average birth weight, babies of smoking mothers have a higher mortality rate, but low birth weight babies of smoking mothers have a lower mortality rate than other low birth weight babies.
References
Quine, W. V. (1962) "Paradox". Scientific American, April 1962, pp. 84–96.
See also
External links
Category:Core issues in ethics\nCategory:Wikipedia Featured Articles\n\n\n\n\n\n\n\nsimple:Paradox\n\n
