Demands for Particular Proof: Appendices

26 Eliezer_Yudkowsky 15 February 2010 07:58AM

Appendices toYou're Entitled to Arguments, But Not (That Particular) Proof

(The main article was getting long, so I decided to move the appendices to a separate article which wouldn't be promoted, thus minimizing the size of the article landing in a promoted-article-only-reader's feed.)

A.  The absence of unobtainable proof is not even weak evidence of absence.

The wise will already know that absence of evidence actually is evidence of absence; and they may ask, "Since a time-lapse video record of apes evolving into humans would, in fact, be strong evidence in favor of the theory of evolution, is it not mandated by the laws of probability theory that the absence of this videotape constitute some degree of evidence against the theory of evolution?"

(Before you reject that proposition out of hand for containing the substring "evidence against the theory of evolution", bear in mind that grownups understand that evidence accumulates.  You don't get to pick out just one piece of evidence and ignore all the rest; true hypotheses can easily generate a minority of weak pieces of evidence against themselves; conceding one point of evidence does not mean conceding the debate; and people who try to act as if it does are nitwits.  Also there are probably no creationists reading this blog.)

The laws of probability theory do mandate that if P(H|E) > P(H), then P(H|~E) < P(H).  So - even if absence of proof is by no means proof of absence, and even if we reject the philosophy that absence of a particular proof means you get to discard all the other arguments about evidence and priors - must we not at least concede that absence of proof is necessarily evidence of absence, even though it may be very weak evidence?

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