622
Opinion of the Court
The burden of showing something by a "preponderance of the evidence," the most common standard in the civil law, "simply requires the trier of fact 'to believe that the existence of a fact is more probable than its nonexistence before [he] may find in favor of the party who has the burden to persuade the [judge] of the fact's existence.' " In re Winship, 397 U. S. 358, 371-372 (1970) (Harlan, J., concurring) (brackets in original) (citation omitted). "A finding is 'clearly erroneous' when although there is evidence to support it, the reviewing [body] on the entire evidence is left with the definite and firm conviction that a mistake has been committed." United States v. United States Gypsum Co., 333 U. S. 364, 395 (1948). A showing of "unreasonableness" would require even greater certainty of error on the part of a reviewing body. See, e. g., Anderson v. Liberty Lobby, Inc., 477 U. S. 242, 252 (1986).
In creating the presumption at issue, these terms are combined in a very strange way. As our descriptions indicate, the first, "preponderance," is customarily used to prescribe one possible burden or standard of proof before a trier of fact in the first instance, as when the proponent of a proposition loses unless he proves a contested proposition by a preponderance of the evidence. The term thus belongs in the same category with "clear and convincing" and "beyond a reasonable doubt," which are also used to prescribe standards of proof (but when greater degrees of certainty are thought necessary). Before any such burden can be satisfied in the first instance, the factfinder must evaluate the raw evidence, finding it to be sufficiently reliable and sufficiently probative to demonstrate the truth of the asserted proposition with the requisite degree of certainty.
The second and third terms differ from the first in an important way. They are customarily used to describe, not a degree of certainty that some fact has been proven in the first instance, but a degree of certainty that a factfinder in the first instance made a mistake in concluding that a fact
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