I contend that these peculiar rules are two of the most successful social conventions which the human species has ever evolved. Put them into effect, and you have laid the groundwork for a knowledge-producing and dispute-resolving system that beats all competitors hands down. They are the basis of liberal inquiry and of science. Everything that follows in this essay is ultimately an attempt to defend them, and the attacks of the creationists and humanitarians and others are ultimately attempts to undermine them.

First, the skeptical rule. If people follow it then no idea, however wise and insightful its proponent, can ever have any claim to be exempt from criticism by anyone, no matter how stupid and grubby-minded the critic. The skeptical rule is,

This is more or less, what the great twentieth-century philosopher of science Karl R. Popper and his followers have called the principle of falsifiability. Science is distinctive, not because it proves true statement, but because it seeks systematically to disprove (falsify) false ones. In practice, of course, it is sometimes hard, if not impossible, to say whether a given statement is falsifiable or not. But what counts is the way the rule directs us to try to act. In principle, if you do not try to check ideas by trying to debunk them, then you are not practicing science. You are entitled to claim that a statement is objectively true only insofar as it is both checkable and has stood up to checking, and not otherwise. Decicions about what is and is not true are always provisional, standing only until debunked.

Second, the empirical rule. If people follow it in deciding who is right and who is wrong, then no one gets special say simply on the basis of who he happens to be. The empirical rule is,

In other words, whatever you do to check a proposition must be something that anyone can do, at least in principle, and get the same result. Who you are doesn't count, the rules apply to everybody, regardless of identity. A test is valid only insofar as it works for anyone who tries it. Where different checkers (debunkers) get different results, no one's result supersedes anyone else's, and no result can be declared. The test remains inconclusive. (It is important to note that "no personal authority" says nothing against expertise. It only says that no one, expert or amateur, gets to claim special authority simply because of who he happens to be or what he is saying. Whatever you do to become an expert must thus be something that others also could do. You may have a Ph.D., but I could get one. The views of experts, no less than those of laymen, are expected to withstand checking.)

Those two rules define a decision-making system which people can agree to use to figure out whose opinions are worth believing. Under this system, you can do anything you wish to test a statement, as long as you follow the rules, which effectively say:

• The system may not fix the outcome in advance or for good (no final say).
• The system may not distinguish between participants (no personal authority).

The rules establish, if you will, a game -- like chess or baseball. And this particular game has the two distinctive characteristics that define a liberal game: if you play it, you can't set the outcome in advance, and you can't exempt any player from the rules, no matter who he happens to be.