Another fallacy of relevance leans on the crowd. It is sometimes called the bandwagon.
Key idea
An appeal to the people argues that a claim is true, or a choice is good, because many people believe it or do it.
Why it works
Large numbers of people have believed false things, and popular choices can be popular for reasons of fashion, price or habit. How many people believe a claim tells us about the people, not about the claim.
Worked example: When popularity is the point
"This cookbook is the best-selling cookbook in the state this year, so it is a very popular cookbook."
- Here the conclusion is about popularity itself.
- Sales are exactly the right evidence for that.
Answer: Not a fallacy.
Worked example: When it is not
"Most of my friends skip breakfast, so skipping breakfast must be good for you."
- The conclusion is about health, not about what is common.
- What many friends do is no evidence about what is good for the body.
Answer: Appeal to the people.
Popularity is also relevant when the question is what people want: if nearly every student votes for tacos at the class party, that is a good reason to serve tacos.
Common mistake
Calling any mention of popularity a fallacy. Popularity is relevant to claims about popularity ("best-selling") and to choices meant to please many people. It is a fallacy when the conclusion is about truth or quality.