When we appeal to popularity, we are suggesting that just because many people believe something, it is true.
Example of appeal to popularity
Premise: Most people believe the Earth is flat.
Conclusion: The Earth is flat.
Why it’s illogical
Much like with the ad hominem fallacy, people believing in a thing doesn’t change its truth.
Oddly, people also like to use the opposite type of reasoning for some arguments – which I like to call the appeal to sheeple, or appeal to free thinking.
In this case, someone will argue that you should believe something because it’s the opposite of what everyone else believes. For instance:
Which can be written as:
Premise: Society wants you to think the Earth is round.
Conclusion: The Earth is not round.