An appeal to the people leans on many voices. An appeal to authority leans on one voice that is supposed to know. Sometimes that is good reasoning; sometimes it is not.
Key idea
Citing an expert in their own field, where experts agree, is reasonable. Citing someone outside their expertise, or one voice against a strong consensus, is the fallacy of appeal to unqualified authority.
Why it works
Nobody can check everything, so we rely on people who know. That reliance is justified only when the person knows about this question. A soccer star knows soccer, not nutrition. One doctor against nearly all doctors gives weak evidence, because the field as a whole is a better guide than one member.
Worked example: Fair
"The pediatrician who has treated children for twenty years says Ava needs to rest her sprained ankle for a week. So Ava should rest it."
- The question is medical, and the doctor is a medical expert.
- Doctors broadly agree on resting sprains.
Answer: A fair appeal to authority.
Worked example: Unfair
"One doctor online says people should never drink water during exercise. Almost all other doctors say the opposite. So Kai stops drinking water at practice."
- The source is a doctor, so the field is right.
- But it is one voice against nearly all experts.
Answer: Appeal to unqualified authority.
Common mistake
Thinking every appeal to authority is a fallacy. We rely on experts all the time, and rightly. Ask two questions: is this person an expert on this very question, and do other experts in the field agree?