An argument from authority is not a fallacy in and of itself. An appeal to false authority is always a fallacy, such as considering an authority's opinion on a

An argument from authority is not a fallacy in and of itself. An appeal to false authority is always a fallacy, such as considering an authority's opinion on a topic on which they're not authoritative. If the participants in a debate agree that an authority is legitimate, then an unchallenged appeal to their authority is not fallacious. If an authority's opinion is contradicted by undisputed evidence, then an appeal to their authority is fallacious. The whole point of the distinction is to admit authority as a valid source of information, in the absence of direct evidence, because we can't possibly reason from direct evidence in every single case.