So far, I have discussed issues about when we should believe experts and what evidence we can use against good expert opinion. However, there is another issue. Most of the time, experts do not say that almost all experts agree with me, and the same number of experts have reasons within our knowledge for that position. They just say “scientists say…” or “we know that…”. So in these situations, can we use the arguments of experts? We cannot. Until we can confirm that the opinion of the experts is good enough, their opinion is no better than ours.
Imagine that you met a stranger at grocery store. This stranger told you that you should not eat the eggs because some of them were rotten. You might become wary of the eggs and avoid buying them. Would the bare claim that he is an expert on eggs somehow make his claim about the rottenness of eggs better? I do not think so. The reason why the stranger’s opinion matters is that it alerts us to something that we may not be checking thoroughly enough. We will check the eggs if have time and know how, but if we do not we will either ask someone who we know is a relative expert on eggs or we will avoid buying them.
Imagine that our situation was different. Now an expert on eggs (on TV) tells you that eggs that have soft shells, are discolored or smell like sulfur are rotten. They also tell you that all experts on eggs will agree on this because of how eggs become rotten chemically. Now you will be able to return to the store and pick up the eggs. They had none of those features so they are not rotten. We are not accepting the expert’s advice because he is alerting us to some problem. We are accepting his advice because we believe it to be true. We have no understanding of why eggs become rotten, or how long it takes for eggs to become rotten or anything else other than what rotten eggs look like. We only know that because the expert said so.
This means that if an expert on eggs says that they are an expert on eggs, says that all experts agree with them and says that all experts believe this for the same reason that she does, then we can believe that opinion as an expert opinion. We can do so just until someone disagrees. If another person comes along and claims that the original person is not an expert, or that he is an expert and all experts do not agree, or that he is an expert and experts do not agree on the reasons for the opinion, then that ‘expert’ opinion is no longer the opinion of an expert. We believe expert opinion because the testimony of the expert is consistent with everything that we already know about what makes that person an expert on that subject. If it should no longer be consistent, then we should not believe that they are an expert any longer.