The rationale for the best evidence rule can be understood from the context in which it arose: in the eighteenth century a copy was usually made by hand by a clerk (or even a litigant). The best evidence rule was predicated on the assumption that, if the original was not produced, there was a significant chance of error or fraud in relying on such a copy.
In the age of digital facsimiles, etc. the rule is more difficult to justify. The likelihood of actual error (as opposed to mere illegibility) through copying is slight. The balance of convenience favours avoiding needless effort and delay where there is no dispute about the fairness and adequacy of a digital facsimile. Further, it is by no means clear what the 'original' of an electronic communication such as an e-mail actually is: as a great many electronic 'copies' of a message might come into existence from creation to receipt.
The best evidence rule is also thought to be the basis for the rule precluding the admissibility of hearsay evidence, although the two rules are now quite distinct.
The rule requires that when writings are introduced as evidence in a trial, the original writing must be produced as the "best evidence". In Federal practice, however, any exact copies of the original carry the same legal weight as the original unless their authenticity is in question.
The term "writing" has been liberally interpreted to include photographs, x-rays, and films. Note that for photographs and film, this could be construed to mean negatives, not prints, as they are the true 'original'.
The rule applies in two situations:
There is an exception. If the original document is unavailable for reasons other than serious misconduct of the proponent, secondary sources of evidence (such as oral testimony) can be used in place of the original.
Currently, both California law and the Federal rules allow the use of mechanically produced duplicates unless a party has raised a genuine question about the accuracy of the copy or can show that its use would be unfair.
The best evidence rule, which was used in the 18th and early 19th centuries as an exclusionary principle, i.e. to prevent the admission of certain evidence where better evidence was available, is now all but defunct.Lord Denning MR has stated:
The old rule, that a party must produce the best evidence that the nature of the case will allow, and that any less good evidence is to be excluded, has gone by the board long ago. The only remaining instance of it is that, if an original document is available on one’s hands, one must produce it; that one cannot give secondary evidence by producing a copy. Nowadays we do not confine ourselves to the best evidence. We admit all relevant evidence. The goodness or badness of it goes only to weight, and not to admissibility.
citing Doe d. Gilbert v. Ross (1840) 7 M. & W. 102, 151 E.R. 696 (Exch.) as the source. This page then provides the clarification that