Some of the smartest people in the world believe the silliest things. Everyone from St Augustine to Isaac Newton. They can be simultaneously dead right about some things and dead wrong about others. It is the best example going against "argument by authority".

Perhaps it has something to do with taste, and opinion. Why does someone root for one athletic team and boo another? Not just soccer hooligans either, but sometimes very clever and reasonable people. Why do some people prefer country to rock, or Bach to Mozart? I have mentioned before here that one of my closest friends has an MS in organic chemistry from Columbia, but he believes in ghosts, telepathy, clairvoyance, channelling and a host of other paranormal phenomena. On the other hand, he does NOT believe in Atlantis, Bigfoot, UFOs or the Bermuda Triangle, and for pretty much the same reasons I don't.

My best example is a paleontologist I knew when I worked for Gulf Oil in Pittsburgh, whose professional specialty was dating rock strata by their microfossils. This man could successfully carry out his duties, which are grounded in and made possible by the discoveries of evolutionary biology and geology, but he was a fundamentalist Christian and sincerely believed the world was 6000 years old. When I pressed him on how this could be, his response was "I just identify the geological eras, others have supplied the time ranges".

The fact that this happens is undeniable, and since it happens to others who are totally unaware of it, we can never rule out that we do it too without our knowledge. So how do you avoid this? Well, there is no sure way to do it. But you can take steps to minimize the chances that you are doing it. First, you adopt a scientific methodology, the whole program, scientific method, experimental verification, peer review, professional consensus, rules of evidence, adherence to logic, systematic skepticism, etc. It must be emphasized this does not guarantee freedom from error, but it does reduce the possibility.

The Law is an alternative system with procedural and precedent rules for determining truth, too. And even though it is biased towards the innocent (false positives are much more discouraged than false negatives) it still fails frequently in determining both the guilty and the innocent. Science also has a bias, it tends to favor orthodoxy, things that are known to work now. Because of this, it is accused of closed-mindedness and overconservativism, but it is a deliberate bias like that of the law, which feels it is better for the guilty to go free than for the innocent to be punished. Science would rather disbelieve the truth than believe something which was false. And we must never forget that sometimes scientists just interpret the data differently. Science is filled with disagreement and controversy, and sometimes conflict and hostility, too.

In any field, there are some things which may be true but simply cannot be proven, one way or another. Even mathematics has its Incompleteness Theorems. If someone told me there was a secret alien base on the moon I'd tell him he was crazy because it's not likely he was able to know that without my knowing it too. We have access to the same data. But we cannot rule out there IS a secret alien base on the moon, can we? Still, I don't have to disprove it, it is up to others to convince me.

So what evidence do I have that this system is better than some other?
Science is able to predict events that other belief systems cannot. And scientific principles can be used to make devices which function properly. A deeply religious sailor may be able to navigate his ship safely to harbor, but he used his almanac, his clock and his sextant to do so, not his scripture or his prayer.