fallacy

Bandwagon fallacy

Also called: Appeal to popularity, Argumentum ad populum

The bandwagon fallacy argues that a claim is true, or a choice is right, because many people believe or do it.

How it works

Social proof is a powerful shortcut, and popularity can be weak evidence in some domains. But large numbers of people have been wrong many times, and popularity can be manufactured through repetition or selective polling.

Examples

"Millions of people use this remedy, so it must be effective."

Wide use shows popularity, not effectiveness; only controlled evidence can show that.

"Everyone in the office is backing the proposal, so you should too."

The reasons for the proposal, not the head count, should decide your view.

How to spot it

"Everyone knows", "most people agree", "join the millions".
Numbers of supporters are given, but not reasons.
Pressure to conform rather than to evaluate.

How to respond

Ask why the many believe it and whether those reasons hold.
Check whether the popularity figure itself is reliable.
Note when the crowd is relevant, such as for questions about conventions or preferences.