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Argumentum ad populum ("argument to the people") is a logical fallacy that occurs when something is considered to be true or good solely because it is popular. Undoubtedly many popular notions are true, but their truth is not a function of their popularity, except in circumstances where other factors ensure that popularity correlates with truth. The fallacy is the opposite of an appeal to the minority.
 Alternate names
- appeal to popularity
- appeal to numbers (argumentum ad numerum)
- consensus gentium
- appeal to majority
- appeal to mass opinion
- appeal to popular prejudice
- appeal to the gallery
- appeal to the mob
- argument by consensus
- authority of the many
- bandwagon fallacy
- common belief
- democratic fallacy
P1: X is popular.
P2: (unstated) Popular things are true.
C1: X is true.
 Bandwagon variant
P1: X is popular/gaining popularity.
P2: (unstated) I should do what is popular.
C1: I should do X.
The argument is problematic because unfortunately, the premise "the majority is always right" may not be true. When phrased like this, few people would say that they'd fall for such a stupid thing - but it's still a remarkably easy trap to fall into, precisely because people don't realise that it's a bandwagon that they're jumping on. In a manner similar to the Matthew effect[wp], something that gains attention (legitimately or otherwise) will attract more interest. This interest generates more interest, like an internet meme circulating around internet forums, and before you know it everyone is on the bandwagon shouting "yee haw!!" While this is merely just how information tends to propagate, the bandwagon argument truly becomes fallacious when people use it as an excuse to say that an issue is important or that the circulating opinion must be correct.
It should be noted that it is not necessary for the facts to get in the way of a good argument, the bandwagon has its own momentum and will carry its passengers whether true or not.
Sometimes, when events are due to external causes, both political sides will jump onto the same bandwagon and each will accuse the other of doing so (for example, terrorism).
 Legitimate use
When the truth-value of the proposition is really a function of the popularity. This can arguably be the case in grammar (most native speakers think a certain construction is grammatical, thus it is grammatical),and matters of convention and etiquette.
The idea that groups of people are better at decision making than the individual is the cornerstone of voting and governmental systems such as democracy. It is also the key component of Wikipedia, where the contributions of many editors over time will produce a reliable and good quality article and of news aggregation sites (RationalWiki's WIGO system being one example) where articles are voted up/down based on group consensus.
 Scientific consensus
What's the difference between most people believe X and scientific consensus which is, at the end of the day, most scientists believe X? Doesn't this make out scientists to be somehow superior to the rest of the population?
There are two significant differences:
- Scientific consensus doesn't claim to be true, it claims to be our best understanding currently held by those who study the matter. Scientific claims for truth are always tentative rather than final, even if they are often very impressive tentative claims for truth.
- Scientific consensus is built upon a foundation of logic and systematic evidence - the scientific method - rather than popular prejudice. The consensus comes not from blindly agreeing with those in authority, but from having their claims to be thoroughly reviewed and criticised by their peers. (Note that even long-established scientific consensus can be overthrown by better logic and better evidence typically preceded by anomalous research findings.)
This logical fallacy is often used by children as an excuse for wanting something (everybody's got one) or getting into mischief (everybody's doing it). Despite the juvenile nature of the argument, it is often used by people who should know better, particularly by those who are trying to force other people to their way of thinking. A case in point is the push in the United States to get creationism taught in public school science classes. The argument runs along the lines of suggesting that because a majority of people in the U.S. believe in creationism, it should therefore be taught as science.
 Fifty million Frenchmen
"Fifty million Frenchmen can't be wrong" is used, though often sarcastically, to justify a point of view by alluding to its general acceptance. It is a demonstration of argumentum ad populum and is falsified prima facie by the French obsession with Jerry Lewis as a comic genius in the 1960s. It derives from the 1927 song "Fifty Million Frenchmen Can't Be Wrong" which compared free attitudes in 1920s Paris with censorship and prohibition in the United States.
It has also been noted that "The entire population of Germany can't be wrong twice."[citation NOT needed]
 Argumentum ad populum... without the populum
A twist on the argumentum ad populum is claiming that some idea is more popular than it is, and then using that alleged popularity in order to justify some extreme measures against the alleged promoters of the idea. Examples include:
- Christian fundamentalists countering Islamic terrorists' farm system of suicide bombers by brainwashing children into thinking "we are enlisted in the holy military service of Christ that all our life long we should fight against the world, Satan, and our own flesh," as shown in the documentary Jesus Camp.
- The claims of Joseph McCarthy and the John Birch Society that there was a massive secret communist conspiracy to subvert the First World and capture it for the Soviet Union.
- The claims underlying homosexual recruitment conspiracy theories, as well as Bill O'Reilly's chatter about a lesbian gang epidemic: that an idea of homosexuality as superior to heterosexuality is commonplace among the gay population, thus justifying their exclusion from schools etc.
- Some exaggerated claims by such organs as Searchlight magazine about the popularity of the British National Party, positing that the party might turn Britain into a fascist dictatorship sometime next week and start curtailing civil rights. This, the magazine argues, means that the civil rights of all persons even tangentially associated with the BNP must be promptly curtailed.
The term "silent majority" is often invoked by people who decide to fall back on argumentum ad populum without any actual evidence that their view is at all popular. The flaw with the phrase is obvious: if the majority is silent, then how can one identify its views?
 Wisdom of the crowd
The wisdom of the crowd (from the 2004 book The Wisdom of Crowds) is a perceived phenomenon whereby groups of people can make better informed decisions than individuals alone. If crowds were truly wiser than individuals, this would suggest that an argumentum ad populum could be true, at least in certain circumstances.
Most of the evidence for such phenomena are entirely anecdotal.
The original observation was supposedly seen at a church or village fair (or fête or wherever) in the 19th century, where the crowd were asked to guess the weight of a pig (or the number of beans in a jar, you know the sort of game). Of course, estimates vary wildly for this sort of thing, from sensible answers to outright embarrassing answers. The majority of these answers would, of course, be completely wrong, and it is possible that not a single one could be right. However, one observer noted that if you took all the answers, and calculated the arithmetic mean of them, not only was the answer very close, but it was exactly right. Hence the crowd, collectively, could calculate better than an individual.
 Situational success
Some evidence suggests that this sort of works, but only in certain situations. Namely, situations where the knowledge required is very well defined. This can be seen in the game show Who Wants to be a Millionaire where a player can ask the audience for an answer out of 4 possible ones. Here, the audience can be split into two groups; those that know the answer, and those who don't. Those who don't know the answer will, in theory, select randomly and on average, these answers will be uniformly distributed amongst the possible answers. This leaves the people who know the answer, who will choose the correct one and bring that answer above average. With the exception of circumstances where the answer may be part of a widely believed myth or the question is ambiguous, the situation works out well on average and the wisdom of the crowd holds.
 Situational failure
The idea of "the wisdom of the crowd" does not hold where the the knowledge is poorly defined. An exact outcome, such as the "number of beans in a jar" discussed above, is very well defined, but the results of the lottery (which Derren Brown cheekily tried to claim he predicted using the "wisdom of the crowd" method) isn't, and thus isn't subject to the method. Similarly, the Who Wants to be a Millionaire scenario works because the questions are on general knowledge, there are limited options and enough of the population will be expected to know the right answer. If the answer was more open-ended, subjective or far fewer individuals would be expected to know the right answer - so few that their contribution would be statistically significant - then the system would fail. The whole wisdom of crowds, therefore, falls short when the "crowd" in question is subject to groupthink or other biases, in including a lack of specialist knowledge.
The lack of specialist knowledge in a crowd is one of the main factors working against "wisdom of crowds" having a universal application to open ended or specialist questions. The majority population at large would not have the knowledge of atmospheric chemistry, climate models, hydrosphere dynamics or many other areas of knowledge to effectively evaluate the effects of climate change on the planet. Indeed, when chess master Gary Kasparov played against "the world", he won. Given that the only way to effectively implement the system in most circumstances is by vote majority consensus, what the majority may believe may not necessarily be right. The high prevalence of some urban legends and conspiracy theories is certainly evidence of this.
 See also
- See the Wikipedia article on Bandwagon fallacy.
- Appeal to Popularity, Bruce Thompson
- Bandwagon, Fallacy Files
- Appeal to the People, Internet Encyclopedia of Philosophy
- Argumentum ad Populum, Agnosticism/Atheism About.com
- Appeal to popularity, Stephen Downes
- Your logical fallacy is bandwagon, YLFI
- ↑ Bill Maher lays waste to global warming deniers
- ↑ Glenn, Cheryl; Loretta Gray. Hodges' Harbrace Handbook. 16th ed. Thomson: Boston, 2007: p. 479.
- ↑ Source of the expression?
- ↑ Second Helvetic Confession (foundational Calvinist creed), chapter XX
- ↑ Full title (deep breath!): The Wisdom of Crowds: Why the Many Are Smarter Than the Few and How Collective Wisdom Shapes Business, Economies, Societies and Nations
- ↑ BBC News - Should we trust the wisdom of crowds?
- ↑ Or out of two if they've already chosen "phone a friend", but it still works out
- ↑ Michael Nielsen - Kasparov versus the World.