Argumentum ad populum

The September update of the OED includes more than 600 new entries, among them is “Argumentum ad populum.”

Argumentum ad populum, also known as an appeal to popularity, is a logical fallacy where one asserts that a proposition must be true or valid simply because many or most people believe it to be so. The fallacy occurs when the popularity of an idea is used as evidence of its truth, rather than examining the actual merits or logical basis of the claim.

For example:

“Most people believe X, therefore X must be true.”

This reasoning is flawed because the popularity of a belief does not necessarily correlate with its accuracy or truthfulness.

But does this contradict the notion of “the wisdom of the crowd”?

Argumentum ad populum and the concept of the wisdom of the crowd may appear similar but they are distinct in their reasoning, and only seem contradictory if misunderstood.

• Argumentum ad populum is a fallacy that assumes a belief is true simply because a large number of people hold it. It focuses on the popularity of an opinion without assessing the validity or quality of the reasoning behind it.

• Wisdom of the crowd, on the other hand, refers to the idea that collective judgments, when aggregated from diverse, independent individuals, can often lead to more accurate conclusions than those made by a single expert. This concept is rooted in probability and collective knowledge, particularly when applied to situations involving estimation, problem-solving, or forecasting.

The wisdom of the crowd is not about blindly following majority opinion (as in argumentum ad populum) but rather about aggregating diverse inputs to derive a more reliable outcome. If the necessary conditions for wisdom of the crowd are not met—such as if the crowd is biased, uncritical, or lacks diversity—then it can devolve into something closer to an argumentum ad populum.