Argumentum ad populum
Argumentum ad populum (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.
- "Fifty million 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?"
Argumentum ad populum comes in two varieties: 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.
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., "XYZ Cola: the official soft drink of the National Football League".
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. 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 studied the matter. In effect, we are trusting that the experts have reached their conclusions through valid arguments, so there is no need for us to research the matter ourselves.