Argumentum ad populum

Argumentum ad populum ("argument from popular appeal", "appeal to the majority") is a logical fallacy whereby a proposition is claimed to be true because it is believed by large numbers of people.

Examples

 * "Fifty million Elvis fans can't be wrong." (See also 50,000,000 Elvis Fans Can't Be Wrong.)
 * "All US presidents have been Christians. Maybe such a prestigious group of people is onto something."
 * "90% of the people in the world believe in God. Are you saying that all of them are wrong?"

Discussion
Argumentum ad populum comes in two varieties:
 * 1) The first is to argue from sheer numbers: "Everyone knows X, so X must be true".
 * This argument is appealing because in many cases, what "everyone knows" is true: the Sun rises in the east, not the south; grass is green; and George Washington was the first President of the United States.
 * This is effective because it pressures people to be "normal". People have a desire to be like their peers. Thus tactics involving alienation are often used to bully people into submission, this is often a sign of a bad argument.
 * 1) The second variety is "snob appeal": A proposition is claimed to be true because it is believed by an elite or distinguished group of people.
 * This argument often appears in advertising, (e.g., "Z Cola: The official soft drink of the Big-Time Sports Event").

Counter-apologetics
Argumentum ad populum is a fallacy because the fact that many people believe something does not make it true. For many years, most people believed that the Earth was the center and most important feature of the universe. Millions of people believe that astrology works. Neither is true.

One special case is that in which a statement is said to be true because it is believed by most of the experts in the field (9 out of 10 dentists recommend Brand X toothpaste!). For example, if most astronomers say that the Earth revolves around the Sun instead of the other way around, then that is very likely to be true. In this case, however, we are trusting the judgment of people who have carefully studied the matter. In effect, we are trusting that the experts have reached their conclusions through valid arguments based on careful observation, so there is no need for us to research the matter ourselves. This type of argument is often reliable, but not always. After all, scientific knowledge is never perfect and complete. However, for most "mature" scientific fields, the likelihood of a complete reversal of views &mdash; such as moving the Earth from the center of the universe to the outskirts of one unremarkable galaxy among millions &mdash; is incredibly, and ever increasingly, small.

Within the ad populum fallacy is the fallacy of appealing to authority, since this argument assumes that the majority hold the authority regarding truth. Counter to the example of the 10 dentists, theological belief is not a skill developed by professionals of the field; rather, it is something accessible to all upon reflection. Under this framework, appealing to theological authority (i.e. the authority of those claiming Christianity to be true) is another fallacy within this argument.