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Philosophy, Preface Paradox


Evidence | Law and Philosophy


Imagine that the preface to a professor’s book implicitly asserts that all the propositions in the rest of his or her book are true, but explicitly acknowledges that experience would suggest some errors remain among those propositions. The prof thereby seems paradoxically to believe inconsistent statements. But in fact this famous preface paradox is an illusion. The first statement is a belief reflecting epistemic uncertainty, while the second is a probabilistic statement about aleatory uncertainty. If one were to convert the probability into a belief, one would see that the author rationally holds perfectly consistent beliefs.

Likewise the lottery paradox resolves. Remarkably, resolution of these philosophy paradoxes sheds important light on legal evidence and proof: once one realizes that legal factfinding deals in beliefs, not probabilities, many of the law’s proof paradoxes vaporize. All those paradoxes reveal a generally applicable and powerful principle of rational thought: if in the presence of epistemic uncertainty a person believes fact x and believes fact y because each passes the threshold for belief, then the person believes x AND y together. The explanation lies in the fact that epistemic uncertainty calls for nonadditive logic, which employs the MIN rule for conjunction rather than the product rule. The significance is broad, as it maps where one can logically believe a string of beliefs as a narrative chain.