Evidence (law)
The
law of
evidence governs the use of
testimony (e.g. oral or written statements, such as an
affidavit) and
exhibits (e.g. physical objects) or other documentary material which is admissible (i.e. allowed to be considered by the
trier of fact, such as
jury) in a
judicial or administrative proceeding (e.g., a
court of law).
In every jurisdiction based on the English common law tradition, evidence must conform to a number of rules and restrictions to be admissible. Evidence must be
relevant — that is, it must have a tendency to make a fact at issue in the proceeding be more or less probable than it would be without the evidence.
However, relevance is ordinarily a necessary condition but not a sufficient condition for the admissibility of evidence. For example, relevant evidence may be excluded if it is unfairly prejudicial, confusing, or cumulative. Furthermore, a variety of social policies operate to exclude relevant evidence. Thus, there are limitations on the use of evidence of
liability insurance,
subsequent remedial measures,
settlement offers, and
plea negotiations, mainly because it is thought that the use of such evidence discourages parties from carrying insurance, fixing hazardous conditions, offering to settle, and pleading guilty to crimes, respectively.
Of all jurisdictions worldwide, the United States of America has the most complicated system of evidentiary rules. The unusual complexity of American evidence law arises from two factors: (1) the right of American defendants to have findings of fact made by a jury in practically all criminal cases as well as many civil cases; and (2) the widespread consensus that tight limitations on the admissibility of evidence are necessary to prevent a jury of untrained laypersons from being swayed by irrelevant distractions (such as the infamous
Chewbacca Defense). Legal historian Lawrence Friedman has explained that "
[a] trained judge would not need all these rules; and indeed, the law of evidence in systems that lack a jury is short, sweet, and clear."
Certain kinds of evidence, such as documentary evidence, may be subject to further restrictions such as the
best evidence rule, which requires certain documents to be produced unless they can shown to be unavailable.
In systems of proof based on the English common law tradition, almost all evidence must be sponsored by a
witness, who has sworn or solemnly affirmed to tell the truth. The bulk of the law of evidence regulates the types of evidence that may be sought from witnesses and the manner in which the interrogation of witnesses is conducted during
direct examination and
cross-examination of witnesses. Other types of evidentiary rules specify the standards of persuasion (e.g., proof beyond a reasonable doubt) that a trier of fact such as a jury must apply when it assesses evidence.
Today all persons are presumed to be qualified to serve as witnesses in trials and other legal proceedings, and all persons are also presumed to have a legal obligation to serve as witnesses if their testimony is sought. However, legal rules sometimes exempt people from the obligation to give evidence and legal rules disqualify people from serving as witnesses under some circumstances.
Privilege rules give the holder of the privilege a right to prevent a witness from giving testimony. These privileges are ordinarily (but not always) designed to protect socially valued types of confidential communications. Some of the privileges that are often recognized are the
marital secrets privilege, the
adverse spousal testimony privilege, the
attorney-client privilege, the
doctor-patient privilege, the
psychotherapist-patient and
counselor-patient privilege, and the
clergy-penitent privilege. A variety of additional privileges are recognized in different jurisdictions, but the list of recognized privileges varies from jurisdiction to jurisdiction; for example, some jurisdictions recognize a social worker-client privilege and other jurisdictions do not.
Witness
competence rules are legal rules that specify circumstances under which persons are ineligible to serve as witnesses. For example, neither a judge nor a juror is competent to testify in a trial in which they are serving in that capacity; and in jurisdictions with a
dead man statute, a person is deemed not competent to testify as to statements of or transactions with a deceased opposing party.
Hearsay is one of the largest and most complex areas of the law of evidence. The default rule is that hearsay evidence is inadmissible. Hearsay is an out of court statement offered to prove the truth of the matter asserted. A party is offering a statement to prove the truth of the matter asserted if the party is trying to prove that the assertion made by the declarant (the maker of the pretrial statement) is true. For example, prior to trial Bob says, "Jane went to the store." If the party offering this statement as evidence at trial is trying to prove that Jane actually went to the store, the statement is being offered to prove the truth of the matter asserted. However, at both common law and under evidence codifications such as the
Federal Rules of Evidence, there are dozens of exemptions from and exceptions to the hearsay rule. One common exception is the
voir dire from a police officer, which is generally excepted in trial.
Different types of proceedings require parties to meet different
burdens of proof, the typical examples being
reasonable doubt,
clear and convincing, and
preponderance of the evidence. Many jurisdictions have burden-shifting provisions, which require that if one party produces evidence tending to prove a certain point, the burden shifts to the other party to produce superior evidence tending to disprove it.
One special category of information in this area includes things of which the court may take
judicial notice. This category covers matters that are so well known that the court may deem them proven without the introduction of
any evidence. For example, if a defendant is alleged to have illegally transported goods across a state line by driving them from
Boston to
Los Angeles, the court may take judicial notice of the fact that it is impossible to drive from Boston to Los Angeles without crossing a number of state lines. In a civil case, where the court takes judicial notice of the fact, that fact is deemed conclusively proven. In a criminal case, however, the defense may always submit evidence to rebut a point for which judicial notice has been taken.
Some rules that affect the admissibility of evidence are nonetheless considered to belong to other areas of law. These include the
exclusionary rule of
criminal procedure, which prohibits the admission in a criminal trial of evidence gained by unconstitutional means, and the
parol evidence rule of
contract law, which prohibits the admission of extrinsic evidence of the contents of a written contract.
Because of its importance to the practice of law, all American
law schools offer a course in evidence, and most require the subject either as a first year class, or as an upper-level class, or as a prerequisite to later courses. Furthermore, evidence is heavily tested on the
Multistate Bar Examination ("MBE") - of the 200
multiple choice questions asked in that test, approximately one sixth will be in the area of evidence. The MBE tests evidence predominately under the
Federal Rules of Evidence, giving little attention to matters for which state law is likely to be inconsistent.
Lawrence M. Friedman,
American Law in the Twentieth Century (New Haven: Yale University Press, 2002), 266.
*
Burden of proof*
Expert witness*
Hearsay*
Falsified evidence*
Spectral evidence (testimony about ghosts or apparitions)
*
Evidence under Bayes theorem*
Direct_evidence
