Legal evidence

Legal evidence is evidence that is the basis for legal decisions. 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) a court of law).

Relevance and social policy
Legal scholars of the Anglo-American tradition, but not only that tradition, have long regarded evidence as being of central importance to the 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 be directed at proving or disproving a legal element.

However, the relevance of evidence 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.

The question of how the relevance or irrelevance of evidence is to be determined has been the subject of a vast amount of discussion in the last 100-200 years. There is now a consensus among legal scholars and judges in the U.S. that the relevance or irrelevance of evidence cannot be determined by syllogistic reasoning– if-then logic– alone. There is also general agreement that assessment of relevance or irrelevance involves or requires judgments about probabilities or uncertainties. Beyond that, there is little agreement. Many legal scholars and judges agree that ordinary reasoning, or common sense reasoning, plays an important role. There is less agreement about whether or not judgments of relevance or irrelevance are defensible only if the reasoning that supports such judgments is made fully explicit. However, most trial judges would reject any such requirement and would say that some judgments can and must rest in part on unarticulated and unarticulable hunches and intuitions. However, there is general (though implicit) agreement that the relevance of at least some types of expert evidence– particularly evidence from the hard sciences– requires particularly rigorous, or in any event more arcane reasoning than is usually needed or expected. There is a general agreement that judgments of relevance are largely within the discretion of the trial court– although relevance rulings that lead to the exclusion of evidence are more likely to be reversed on appeal than are relevance rulings that lead to the admission of evidence.

Under the Federal Rules of Evidence (FRE) Rule 401: "Relevant evidence" means evidence having any tendency to make the existence of any fact that is of consequence to the determination of the action more probable or less probable than it would be without the evidence.

Federal Rule 403 allows relevant evidence to be excluded if its probative value is substantially outweighed by danger of unfair prejudice, confusing or misleading the jury or waste of the court's time. California Evidence Code section 352 also allows for exclusion to avoid "substantial danger of undue prejudice." For example, evidence that the victim of a car accident was apparently a "liar, cheater, womanizer, and a man of low morals" was unduly prejudicial and irrelevant to whether he had a valid product liability claim against the manufacturer of the tires on his van (which had rolled over resulting in severe brain damage).

Presence or absence of a jury
The United States of America has a very complicated system of evidentiary rules; for example, John Wigmore's celebrated treatise on it filled ten volumes. James Bradley Thayer reported in 1898 that even English lawyers were surprised by the complexity of American evidence law, such as its reliance on exceptions to preserve evidentiary objections for appeal.

Some legal experts, notably Stanford legal historian Lawrence Friedman, have argued that the 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. In Professor Friedman's words: "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."

However, some respected observers disagree with the commonplace thesis that the institution of trial by jury is the main reason for the existence of rules of evidence even in countries such as the United States and Australia; they argue that other variables are at work.

Unfairness
Under English and Welsh law, evidence that would otherwise be admissible at trial may be excluded at the discretion of the trial judge if it would be unfair to the defendant to admit it.

Evidence of a confession may be excluded because it was obtained by oppression or because the confession was made in consequence of anything said or done to the defendant that would be likely to make the confession unreliable. In these circumstances, it would be open to the trial judge to exclude the evidence of the confession under Section 78(1) of the Police and Criminal Evidence Act 1984 (PACE), or under Section 73 PACE, or under common law, although in practice the confession would be excluded under section 76 PACE.

Other admissible evidence may be excluded, at the discretion of the trial judge under 78 PACE, or at common law, if the judge can be persuaded that having regard to all the circumstances including how the evidence was obtained “admission of the evidence would have such an adverse effect on the fairness of the proceedings that the court ought not to admit it."

Authentication
Certain kinds of evidence, such as documentary evidence, are subject to the requirement that the offeror provide the trial judge with a certain amount of evidence (which need not be much and it need not be very strong) suggesting that the offered item of tangible evidence (e.g., a document, a gun) is what the offeror claims it is. The authentication requirement has bite primarily in jury trials. If evidence of authenticity is lacking in a bench trial, the trial judge will simply dismiss the evidence as unpersuasive or irrelevant.

Witnesses
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, the state secrets 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
Hearsay is one of the largest and most complex areas of the law of evidence in common-law jurisdictions. 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 exclusions from and exceptions to the hearsay rule.

Circumstantial evidence
Evidence of an indirect nature which implies the existence of the main fact in question but does not in itself prove it. That is, the existence of the main fact is deduced from the indirect or circumstantial evidence by a process of probable reasoning. The introduction of a defendant's fingerprints or DNA sample are examples of circumstantial evidence. The fact that a defendant had a motive to commit a crime is circumstantial evidence.

It is possible to argue that all evidence is ultimately circumstantial, on the premises that no experience whatsoever can directly prove a fact. Recall, however, that courts of law deal with what is reasonable, not with ontology.

Evidence that the defendant lied
Lies, on their own, are not sufficient evidence of a crime. However, lies may indicate that the defendant knows he is guilty, and the prosecution may rely on the fact that the defendant has lied alongside other evidence.

Burdens of proof
Different types of proceedings require parties to meet different burdens of proof, the typical examples being beyond a reasonable doubt, clear and convincing evidence, 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.

Evidentiary rules stemming from other areas of law
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.

Evidence as an area of study
In countries that follow the civil law system, evidence is normally studied as a branch of procedural law.

Nevertheless, 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 predominantly tests evidence under the Federal Rules of Evidence, giving little attention to matters for which state law is likely to be inconsistent.

The doctrine of corroboration is required under Scots law meaning that there must be two different and independent sources in support of each crucial fact. Testimony from some experts, such as coroners or doctors, however, is accepted by the court on the basis of the expert's report alone, therefore requiring no corroboration.