The argument from authority is one of the most commonly used debate tactics for the simple reason that the debater, any debater, can’t know everything about all the topics a debate will inevitably spill into. Contrary to what many theists believe, omniscience doesn’t exist, so an appeal to experts is both useful and necessary...as long as they are in fact honest experts. Unfortunately, the argument from authority is also one of the most common fallacious debate tactics. Lately, I’ve been thinking about the difference.
An easy way of upping the authoritative worth of your given authority is by using consensus of unbiased individuals. A scientific consensus is among the strongest because the consensus centers around experimentation and evidence. You’d be right to ask if there is evidence available, then why is an authority even needed? If I needed to refer to basic principles of physics in my argument, I could easily demonstrate that the equations we learned in school that govern motion actually work. I don’t need to take my teacher’s word for it, I can run basic momentum/acceleration/gravity/whatever experiments myself and observe that the results match what is expected. Authority is only needed when the experimentation goes beyond what I can carry out. I could go gain a higher education and rent time on super computers or particle accelerator to run results that would convince me of such-and-such scientific principle, but I am either unwilling to do this or simply don’t have the resources. In this case, taking the word of a scientific consensus is an acceptable substitute. It is acceptable because the findings and results are repeated by other scientists who have a vested interest in accuracy. If something incorrect as accepted, then everything built on that something will also be incorrect. Things are peer-reviewed and double-blinded to eliminate biases. Competition breeds better science, a concept the often science illiterate free-market capitalists should appreciate, but I digress.
Let’s compare science to history. The evidence in this case are records which have a varying degree of authenticity. Video records are by far the best, followed by audio and the more easily ‘shopped photographic records. These both are only available in the modern age--which can often be backed up with other modern records, even living witnesses on occasion. Moving back in time we only have written records. Before the printing press, these records are subject to deterioration or else revised editions which could have been altered purposefully or incidentally. Remember the childhood game of telephone? Like that. Further back still, these written records are controlled only by the elite minority educated enough to read and write. It’s understood that the further back the records the less reliable they are. The historian with a focus on whatever time period in question surely knows more than I, but I will always remain more skeptical of him or her than a scientist reporting results. For all these reasons it becomes rarer and rarer that historians come to a consensus the older the age in question.
Appealing to a consensus among theologians is more problematic. Whereas science relies on gathering evidence without biases and history relies on interpretations of possibly biased records, theology (in most cases) relies on interpretations of possibly biased records with the intention to justify a bias. Catholics, for example, appeal to the authority of the Church, a group with a vested interest in maintaining their relevancy. Of course there is a consensus among Bishops that the Eucharist is the literal body of Christ, but this is as meaningless to anyone outside the church as a consensus among high schoolers that they shouldn’t have homework on Fridays. Or as I analogize to Catholics, who are often Republicans due to their pro-life stance, a consensus among non tax payers that taxes should be raised isn’t exactly an unbiased consensus.
A motto of the freethinker is to "always question authority." It's a good motto. How do your trusted authorities hold up?