An argumentum ad populum (Latin: "appeal to the people"), in logic, is a fallacious argument that concludes a proposition to be true because many or all people believe it; it alleges that "If many believe so, it is so."

This type of argument is known by several names^[1], including appeal to the masses, appeal to belief, appeal to the majority, appeal to the people, argument by consensus, authority of the many, and bandwagon fallacy, and in Latin by the names argumentum ad populum ("appeal to the people"), argumentum ad numerum ("appeal to the number"), and consensus gentium ("agreement of the clans"). It is also the basis of a number of social phenomena, including communal reinforcement and the bandwagon effect, the spreading of various religious and anti-religious beliefs, and of the Chinese proverb "three men make a tiger".

Examples

This fallacy is sometimes committed while trying to convince a person that a widely popular theory is true.

• 9 out of 10 of my constituents oppose the financial rescue package, therefore it is a bad idea.
• 9 out of 10 of my fellow congressmen favour the financial rescue package, therefore it is a good idea.
• Since 88% of the people polled believed in UFOs, they must exist.
• Since citizens have to pay taxes and are ruled by the government, the state must be a judicial reasoned and rightful institution.

It is sometimes committed when trying to convince a person that widely unpopular theories are false.

• It's silly for you to claim that Hitler would not have attacked the United States if they hadn't entered World War II. Everyone knows that he planned to conquer the world.

The fallacy is commonly found in arguments over ethics:

• Most Americans hold that the Vietnam War was morally wrong. Therefore, the Vietnam War was morally wrong.
• Since most people in the world eat meat, there are no ethical issues involved in meat-eating.
• Christianity is believed in by the greatest number of people in the world[4], so it must be true.

The fallacy is also commonly found in marketing:

• Brand X vacuum cleaners are the leading brand in America. You should buy Brand X vacuum cleaners.
• Watch Show X - the #1 watched show on television!

Other examples:

• Fifty million Elvis fans can't be wrong.
• "All of my friends are doing it"
• "Every society but ours believed in magic; why should we think otherwise?" "Every society but ours thought the sun revolved about the Earth, rather than the other way round. Would you decide the matter by majority vote?" - Isaac Asimov.
• In a court of law, the jury vote by majority, therefore they will always make the correct decision.
• Most analysts consider (at a certain time) Enron Corporation a well-run company with excellent management, so its common stock is a good investment.
• Everyone believes that humans are causing enhanced global warming, so that is without a doubt what is occurring.
• Millions of people downloaded songs from Napster; there's nothing wrong with it.
• Everyone jaywalks here and as long as I look carefully, nothing will happen.^[2]

Explanation

World War I propaganda using argumentum ad populum: everyone else is involved in the war effort, so you should help too.

It is logically fallacious because the mere fact that a belief is widely held is not necessarily a guarantee that the belief is correct; if the belief of any individual can be wrong, then the belief held by multiple persons can also be wrong. If for instance, a logical proof that the answer is A attempted to make the argument that 75% of people polled think the answer is A, there is a 25% chance that the answer is not A. However small the percentage of those polled is distributed among any remaining answers, this chance by definition disproves any guarantee of the correctness of the majority. In addition, this would be true even if the answer given by those polled were unanimous, as the sample size may be insufficient, or some fact may be unknown to those polled that, if known, would result in a different distribution of answers.

This fallacy is similar in structure to certain other fallacies that involve a confusion between the justification of a belief and its widespread acceptance by a given group of people. When an argument uses the appeal to the beliefs of a group of supposed experts, it takes on the form of an appeal to authority; if the appeal is to the beliefs of a group of respected elders or the members of one's community over a long period of time, then it takes on the form of an appeal to tradition.

One who commits this fallacy may assume that individuals commonly analyze and edit their beliefs and behaviors. This is often not the case (see conformity).

The argumentum ad populum can be a valid argument in inductive logic; for example, a poll of a sizeable population may find that 90% prefer a certain brand of product over another. A cogent (strong) argument can then be made that the next person to be considered will also prefer that brand, and the poll is valid evidence of that claim. However, it is unsuitable as an argument for deductive reasoning as proof, for instance to say that the poll proves that the preferred brand is superior to the competition in its composition or that everyone prefers that brand to the other.

Evidence

• One could claim that smoking is a healthy pastime, since millions of people do it. However, knowing the dangers of smoking, we instead say that smoking is not a healthy pastime despite the fact that millions do it.
• One could claim Brad Pitt is the best-looking man in the world, because he is regularly voted such, although the sample he is part of (celebrities) is insufficient.

Exceptions

Appeal to belief is valid only when the question is whether the belief exists. Appeal to popularity is therefore valid only when the questions are whether the belief is widespread and to what degree. I.e., ad populum only proves that a belief is popular, not that it is true.

Democracy

The "correctness" of electoral processes lies in the prior acceptance by the electorate that the outcome of an election shall be enacted no matter what it is.

• "Most of the voting members at the last Rotary Club meeting thought that the Club should hold a fund-raiser in October. Therefore, the Club shall hold a fund-raiser in October."
• The people have spoken^[3]

Democracy by the common plurality voting system is based on appeal to popularity. As a means of determining the truth of beliefs, it is fallacious. Democracy does not obviate this; it merely makes the fallacy irrelevant by defining law as subjective rather than objective.

Argumentum ad populum explains how some democracies have fallen victim to the tyranny of the majority. (See Propaganda and Nazi Germany.)

Social convention

Matters of social convention, such as etiquette or polite manners, depend upon the wide acceptance of the convention. As such, argumentum ad populum is not fallacious when referring to the popular belief about what is polite or proper:

• "Most people in Russia think that it is polite for men to kiss each other in greeting. Therefore, it is polite for men to kiss each other in greeting in Russia."

Social conventions can change, however, sometimes very quickly. Thus, the fact that everyone in Russia this year thinks that it is polite to kiss can't be used as evidence that everyone always believed that, or that they should always believe it.

The philosophical question of moral relativism asks whether such arguments apply to statements of morals.

Safety

Whether to follow a tenet decided by popularity rather than logical design may be a matter of safety or convenience:

• "Nearly all Americans think that you should drive on the right side of the road. Therefore, you should drive on the right side of the road in the United States."

In this case, the choice of which side to drive on is basically arbitrary. However, to avoid head-on collisions, everyone on the road must agree on it. In many cases, what is safe to do depends on what others expect one will do, and thus on the "popularity" of that choice.

References

4.http://www.adherents.com/Na/Na_173.html

See also

• Cognitive dissonance
• Communal reinforcement
• Consensus reality

• Conventional wisdom
• Fundamental attribution bias
• Groupthink

• Reductio ad Hitlerum
• Scientific Consensus
• The Wisdom of Crowds
• Three men make a tiger

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