Appeal to authority is not not deductively valid and thus it's logical fallacy. On the other hand very little can be learned with deductive reasoning at once.

Appeal to authority is not not deductively valid and thus it's logical fallacy. On the other hand very little can be learned with deductive reasoning at once. Deductive chains in debate are very short and shortcuts must be used. Authority can be used to weigh or prioritize evidence. If you are not doing serious research into the subject, authority is one heuristic that works extremely well. For example, when two relatively ignorant layman debate in the internet and have limited interest or effort invested to get into the truth. Finding out that something is mainstream view among authorities in the field should end the argument for the time being for the lack of more information. Unfortunately the discussion usually ends with questioning that particular field, then the progress of the society as a whole. Scientists have been wrong before so .. they can also be corrupt ...