Edward K. Cheng

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Vanderbilt Law Review

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rules of evidence, FRE, privilege law, preliminary questions of fact, expert evidence


Evidence | Law


Prior to the eighteenth century, cartographers would often fill uncharted areas of maps with sea monsters, other artwork, or even rank speculation—a phenomenon labeled “horror vacui,” or fear of empty spaces. For example, in Paolo Forlani’s world map of 1565, a yet to-be-discovered southern continent was depicted with anticipated mountain chains and animals. The possible explanations for horror vacui are varied, but one reason may have been a desire “to hide [the mapmakers’] ignorance.” Not until “maps began to be thought of as more purely scientific instruments . . . [did] cartographers . . . restrain their concern about spaces lacking decoration in the interest of presenting their work as modern and professional.”

The law of evidence shares something of a kinship with those old maps. The Federal Rules of Evidence (“FRE”), perhaps the most successful codification project in the history of American law, have advanced the field in incalculable ways, but to treat them as the last word would be a grave mistake. For one thing, the FRE have significant gaps, empty spaces in need of exploration. The most obvious example is the law of privileges, where Congress rejected the rule writers’ proposed codification in favor of retaining the common law. More fundamentally, the FRE are almost entirely about admissibility, the sifting of existing evidence. They say little, if anything, about how evidence is weighed, and they do not typically reflect a concern for party incentives to collect or preserve evidence in the first place.

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Evidence Commons



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