3/26/2008.

There are only 2 possible reasons there could be a consensus - either it is coincidence, or there is some objective factual basis for the common conclusion. If you ask 10 people a question that has 2 possible answers and 9 of them give the same answer, only 2 things are possible:

1) The fact that 9 people gave the same answer is a coincidence and that doesn't make the answer they give any better, more correct, or more worthy of forming a basis for action than the other answer, or.

2) There is some reason they all gave the same answer, a reason that could (at least in principle) be discovered and used by a single person to reach the same answer for the same reason in the absence of any consensus.

A consensus that doesn't have a rational basis is no more worthy of forming a basis for action than any other coincidence.

So suppose we discover that some specific conclusion, X, has a consensus. It's possible this consensus is based on rational evaluation but it's also possible that it's not. If it's not, the fact that there's a consensus tells us nothing about X's truth, usefulness, or validity. We should not accept X or act on X just because of such a consensus. It would be an error to do so.

On the other hand, if the consensus has a rational basis, and is only valid because of it, why not say that it is the rational basis that is valid? That is, X is so (or we should believe it is so) because it has a rational basis.

If we should accept all and only those ideas that have a rational basis to the extent the basis justifies the idea, then what do we need consensus for? How does it help us to know that there is a consensus or isn't a consensus?

Information that is useful or not useful is something that can be analyzed. Other people's opinion on its usefulness or non-usefulness doesn't tell us how useful or not useful it is.

If there is no rational basis for the consensus, the consensus doesn't validate the thing over which there is a consensus. If there is a rational basis, what does the consensus add to the rational basis that isn't there already?

If we have a good reason to accept something, probably most people will accept that thing and a consensus will form around it. But the consensus is not the reason to accept the thing, the good reason is. A consensus that forms without a good reason tells us nothing more than that there is a consensus.