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Any matter of fact that a party to a lawsuit offers to prove or disprove an issue in the case. A system of rules and standards that is used to determine which facts may be admitted, and to what extent a judge or jury may consider those facts, as proof of a particular issue in a lawsuit.

Until 1975, the law of evidence was largely a creature of the common law: Evidence rules in most jurisdictions were established by cases rather than by organized, official codifications. Legal scholars long pushed for legislation to provide uniformity and predictability to the evidentiary issues that arise during litigation. Following a lengthy campaign begun by the American Law Institute, which drafted its Model RULES OF EVIDENCE in 1942, and the National Conference of Commissioners on Uniform State Rules, which drafted the Uniform Rules of Evidence in 1953, Congress in 1975 adopted the federal rules of evidence. The Federal Rules of Evidence are the official rules in federal court proceedings. Most states now also have codified rules of evidence based on these federal rules. Both state and federal rules of evidence serve as a guide for judges and attorneys so that they can determine whether to admit evidence—that is, whether to allow evidence to be observed by the judge or jury making factual conclusions in a trial.

One important benchmark of admissibility is relevance. Federal Rule of Evidence 402 states, in part, "All relevant evidence is admissible, except as otherwise provided." The goal of this rule is to allow parties to present all of the evidence that bears on the issue to be decided, and to keep out all evidence that is immaterial or that lacks probative value. Evidence that is offered to help prove something that is not at issue is immaterial. For example, the fact that a defendant attends church every week is immaterial, and thus irrelevant, to a charge of running a red light. Probative value is a tendency to make the existence of any material fact more or less probable. For instance, evidence that a murder defendant ate spaghetti on the day of the murder would normally be irrelevant because people who eat spaghetti are not more or less likely to commit murder, as compared with other people. However, if spaghetti sauce were found at the murder scene, the fact that the defendant ate spaghetti that day would have probative value and thus would be relevant evidence.



The most common form of evidence is the testimony of witnesses. A witness can be a person who actually viewed the crime or other event at issue, or a witness can be a person with other relevant information—someone who heard a dog bark near the time of a murder, or who saw an allegedly injured plaintiff lifting weights the day after his accident, or who shared an office with the defendant and can describe her character and personality. Any competent person may testify as a witness, provided that the testimony meets other requirements, such as relevancy.

The Federal Rules of Evidence contain broad competency requirements. To testify, a witness must swear or affirm that he or she will testify truthfully; possess personal knowledge of the subject matter of the testimony; have the physical and mental capacity to perceive accurately, record, and recollect fact impressions; and possess the capacity to understand questions and to communicate understandably, with an interpreter if necessary. When an issue of state law is being determined, the state rules of evidence govern the competency of a witness. States that have not adopted the Federal Rules of Evidence may have other grounds for incompetency, such as mental incapacity, immaturity, religious beliefs, and criminal convictions. The Federal Rules of Evidence and most jurisdictions state that jurors and presiding judges are not competent to testify in the case before them.

To be admissible, testimony must be limited to matters of which the witness has personal knowledge, meaning matters that the witness learned about using any of his or her senses. Second, the witness must declare under oath or affirmation that the testimony will be truthful. The purpose of this requirement is to "awaken the witness' conscience and impress the witness' mind with the duty to [be truthful]" (Fed. R. Evid. 603). The oath or affirmation requirement also serves as a ground for perjury if the witness does not testify truthfully. Although the oath frequently invokes the name of God, the witness need not possess any religious beliefs; a secular affirmation is sufficient.

Witnesses may be called to testify by any party to the lawsuit. The party who calls a witness to testify generally questions the witness first, in what is known as direct examination. The judge may exercise reasonable control over the questioning of witnesses in order "(1) to make the interrogation and presentation effective for the ascertainment of the truth; (2) to avoid needless consumption of time, and (3) to protect the witnesses from harassment, or undue embarrassment" (Fed. R. Evid. 611(a)). Thus, the judge may prevent a witness from rambling in a narrative fashion and may require an attorney to ask specific questions in order to ascertain the truth quickly and effectively.

The federal rules and most jurisdictions discourage the use of leading questions on direct examination. These are questions that are designed to elicit a particular answer by suggesting it. For example, the question "Didn't the defendant then aim the gun at the police officer?" is a leading question, and normally it would not be permitted on direct examination. By contrast, "What did the defendant do next?" is a nonleading question that would be permitted on direct examination. In most cases, questions that can be answered with either "Yes" or "No" are considered to be leading questions. Courts generally will permit leading questions during direct examination if the witness is adverse or hostile toward the questioning party.

Leading questions are permitted, and are common practice, during cross-examination. Once a party conducts a direct examination, the opposing party is entitled to cross-examine the same witness. The scope of questions asked during cross-examination is limited to the subject matter that was covered during direct examination, and any issues concerning the witness's credibility. Attorneys use cross-examination for many purposes, including eliciting from a witness favorable facts; having the witness modify, explain, or qualify unfavorable versions of disputed facts elicited during direct examination; and impeaching, or discrediting, the witness.

If a witness is a lay witness (i.e., not testifying as an expert), the witness generally may testify as to facts and not as to opinions or inferences, unless the opinions or inferences are "(a) rationally based on the perception of the witness and (b) helpful to a clear understanding of the witness' testimony or the determination of a fact in issue" (Fed. R. Evid.). For example, a witness may not testify that she smelled marijuana unless she can sufficiently establish that she knows what marijuana smells like. Lay witnesses commonly testify about such things as the speed that a car was going, or someone's approximate age, but these types of inferences are less likely to be permitted the more closely they address critical issues in the case.

Expert Witnesses

"If scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue, a witness who is qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise" (Fed. R. Evid. 702). The admissibility of expert testimony hinges on whether such testimony would help the judge or jury, and whether the witness is properly qualified as an expert. Expert witnesses may, and usually do, testify in the form of an opinion. The opinion must be supported by an adequate foundation of relevant facts, data, or opinions, rather than by conjecture. Thus, an expert frequently relies on firsthand or secondhand observations of facts, data, or opinions perceived prior to trial, or presented at trial during testimony or during a hypothetical question posed by an attorney. Courts do not require experts to have firsthand knowledge of facts, data, or opinions because experts in the field do not always rely on such firsthand knowledge. For instance, physicians routinely make diagnoses based on information from several sources, such as hospital records, X-ray reports, and opinions from other physicians.

When an expert offers a scientific fact as substantive evidence or as the basis of his or her opinion, the court must determine the reliability of the scientific fact by looking at such things as the validity of the underlying scientific principle, the validity of the technique applying that principle, adherence to proper procedures, the condition of instruments used in the process, and the qualifications of those who perform the test and interpret the results. Issues frequently arise over such scientific tools and techniques as lie detectors, DNA testing, and hypnosis. Some scientific tests, such as drug tests, radar, and paternity blood tests, generally are accepted as reliable, and their admissibility may be provided for by statute.

In Kumho Tire Co. v. Carmichael 526 U.S. 137, 119 S.Ct. 1167, 143 L.Ed.2d 238 (U.S.Ala., Mar 23, 1999) (NO. 97-1709), a tire on the vehicle driven by Carmichael blew out, and the vehicle overturned, killing one passenger and injuring others. The survivors and decedent's representative brought a diversity suit against Kumho, the tire's maker, and its distributor. Their claim that the tire was defective relied mainly upon the depositions of a tire-failure analyst, whose expert testimony was to have been that a defect in the tire's manufacture or design caused the blow-out. The expert's opinion was based upon an inspection of the tire and upon the theory that in the absence of certain symptoms indicating tire abuse, a failure of the sort that occurred was caused by a defect. Kumho moved to exclude the expert's testimony, claiming that his methodology failed to satisfy Federal Rule of Evidence 702, which does not distinguish between "scientific" knowledge and "technical" or "other specialized" knowledge. The U.S. Supreme Court disagreed and ruled that the trial judge has the power to test the reliability of all expert testimony, whether by a scientific expert or by an expert who is not a scientist. The court held that Rule 702 does not address the testimony of scientists only, but that it applies to any type of expert testimony.

The American Medical Association maintains guidelines for physicians who testify both as treating physician experts and as nontreating expert witnesses. Many state medical associations also have guidelines for doctors who testify.


The credibility of any witness's testimony depends upon three factors: (1) whether the witness accurately perceived what he or she described; (2) whether the witness retained an accurate memory of that perception; and (3) whether the witness's narration accurately conveys that perception. In order to be allowed to testify, the witness generally must take an oath, must be personally present at the trial, and must be subjected to cross-examination. These conditions promote the factors that lend themselves to the witness's credibility. The rule against hearsay further bolsters the oath, personal presence, and cross-examination requirements.

Hearsay is a statement, made out of court, offered in court to prove the truth of the matter asserted. The statement may be oral or written, or it may be nonverbal conduct intended as an assertion, such as pointing to a crime suspect in a police line-up. The act of pointing in response to a request for identification is the same as stating, "He did it." Not all nonverbal conduct is intended as an assertion, of course. For example, a person usually opens an umbrella to stay dry, not to make the assertion, "It is raining."

Sometimes, statements made out of court are not hearsay because they are not offered for the purpose of proving the truth of the matter asserted. For example, suppose that a man who

claims that a collision between his car and a truck rendered him unconscious files a lawsuit against the truck driver for negligence. The truck driver wishes to introduce as evidence a statement that the man made seconds after the accident: "I knew I should have gotten my brakes fixed; they haven't been working for weeks!" If the purpose of offering the statement is only to prove that the man was conscious and talking following the accident, the statement is not hearsay. However, if the statement is offered to prove that the man's brakes were not working and therefore that he caused the accident, then the statement is offered for its truth, and it is hearsay.

The Federal Rules of Evidence state generally that hearsay is not admissible evidence. The reason is that it is impractical, and in most cases simply impossible, to cross-examine the declarant of an out-of-court statement, or to have the declarant take an oath prior to making the statement. Thus, the credibility of an out-of-court statement cannot be easily ascertained. But the hearsay doctrine is extremely complex. Under the federal rules, for example, most admissions of guilt are not considered hearsay and are therefore admissible, even though they might be stated out of court and then offered as evidence. The federal rules list more than 25 exceptions to the general hearsay prohibition. These exceptions apply to circumstances believed to produce trustworthy assertions.

Some exceptions to the hearsay rule require that the person who made the statement be unavailable to testify at trial. One example of this is when a person who is mortally wounded makes a statement about the cause of her death, just before dying. Under this hearsay exception, the victim's statement assigning guilt or causation is made admissible because the victim is not available to testify at trial, and the need for the information is given greater weight than the fear that she lied. Some have argued that the dying declaration exception exists at least in part because of the belief that persons would not waste their last breaths to utter a falsehood. One federal court commented, "More realistically, the dying declaration is admitted because of compelling need for the statement, rather than any inherent trustworthiness" (United States v. Thevis, 84 F.R.D. 57 [N.D. Ga. 1979]). This exception proved noteworthy in the October 1995 trial and ultimate conviction of Yolanda Saldivar, who was accused of gunning down tejana singing star Selena Quintanilla Perez in a Corpus Christi, Texas, motel. Motel employees testified that Selena's last words before collapsing and dying were, "Lock the door! She'll shoot me again!" and "Yolanda Saldivar in Room 158." Saldivar received a sentence of life in prison following her conviction of murdering the 23-year-old recording artist.

Under some circumstances, the availability of the declarant to testify is immaterial. For example, the excited-utterance exception to the hearsay rule allows the admission of an out-of-court statement "relating to a startling event or condition made while the declarant was under the stress of excitement caused by the event or condition" (Fed. R. Evid.803(2)). The premise for this exception is that excitement caused by the event or condition leaves a declarant without sufficient time or capacity for reflection to fabricate, thus the statement is considered truthful. An example of an admissible excited utterance is the statement, "Look out! That green truck is running a red light and is headed toward that school bus!" Other examples of hearsay exceptions include statements of medical diagnosis, birth and marriage certificates, business records, and statements regarding a person's character or reputation.

Authentication and Identification

Evidence is not relevant unless its authenticity can be demonstrated. A letter in which the defendant admits her guilt in a tax-fraud trial is inadmissible unless the prosecution can first show that the defendant actually wrote it. Blood-stained clothing is irrelevant without some connection to the issues of the trial, such as evidence that the clothing belonged to the accused murderer. The process of linking a piece of evidence to a case—of authenticating or identifying the evidence—is frequently referred to as laying a foundation. Under the Federal Rules of Evidence, a foundation is sufficient if a reasonable juror would find it more probably true than not true that the evidence is what the party offering it claims it to be.

The most basic way to lay an evidentiary foundation is to demonstrate that a witness has personal knowledge. For example, the witness may testify that he wrote the letter, or that he saw the plaintiff sign the contract, or that he found the bullet in the kitchen. When the evidence is an object, the witness must testify that the object introduced at the trial is in substantially the same condition as it was when it was witnessed.

Objects that are not readily identifiable often must be authenticated through chain-of-command testimony. In the case of a blood sample, a proper foundation would include testimony from each individual who handled the blood—from the nurse who drew the blood, to the lab technician who tested it, to the courier who delivered it to the courthouse for trial. Unless each individual can testify that the blood sample's condition remained substantially the same from the time it was drawn until the time it was offered as evidence (accounting for any loss in amount, due to testing), the court could sustain an objection from the other side. The sample then would be inadmissible for lack of authentication.

Under the Federal Rules of Evidence, some evidentiary items are self-authenticating and need no additional authentication before being admitted. Documents containing the official seal of a government unit within the United States, and certified copies of public records such as birth certificates, are self-authenticating, as are newspapers and congressional documents.

Polygraph Tests

In United States v. Scheffer, 523 U.S. 303, 118 S.Ct. 1261, 140 L.Ed.2d 413 (U.S., Mar 31, 1998) (NO. 96-1133), the U. S. Supreme Court upheld a military court evidence rule, Rule 707, which prohibits the use of polygraph, or lie detector, test results in military trials. Scheffer, a military investigator, took a routine urine test, which came back positive for amphetamines. Scheffer then asked for, and was given, a polygraph test which showed that he had no knowledge of amphetamine use. At his trial on drug-use charges based on the urine test, Scheffer tried to introduce evidence of his favorable lie-detector results. The court refused to admit this evidence on the basis of military evidence Rule 707. Scheffer appealed, claiming that he should have been able to introduce the test results as part of his constitutional right "to prepare a defense". The Court upheld the exclusion of the lie-detector test on the grounds that there is too much controversy about the reliability of lie-detector test results; that lie-detector tests might undercut the role of the jury in assessing witness credibility; and that lie-detector tests create too much possibility of side issues about the reliability of the test.

The Best-Evidence Rule

The Best-evidence rule is a misleading name for the courts' preference for original writings, recordings, and photographs over copies, when the contents are sought to be proved. The purpose of this rule at common law was to avoid the potential for inaccuracies contained in handmade copies. The current rule contained in the Federal Rules of Evidence requires the use of original writings, recordings, and photographs (including X-rays and motion pictures), but the rule defines original to include most photocopies or prints from the same negative. The risk of inaccuracies from these types of duplicates is almost non-existent. When the original evidence is lost, destroyed, unobtainable, or in the possession of the opponent, the court will not require a party to produce the original.

Judicial Notice

Some matters that are relevant to a trial are so obvious that a court will not require evidence to prove them—for example, that it is dark outside at midnight, or that April 30, 1995, fell on a Sunday. To prevent wasting a court's time, the rules of evidence permit courts to take judicial notice of such matters; that is, to accept them as true without formal evidentiary proof. Courts may take judicial notice of facts that are generally known to be true (e.g., that gasoline is flammable) or facts that are verifiable from dependable sources (e.g., that Des Moines, Iowa, is in Polk County, which can be verified on a map). As a matter of course, courts judicially notice the contents of laws of and within the United States.


It is a basic tenet in U.S. Jurisprudence that "the public … has a right to every [person's] evidence," and that parties in litigation should avail themselves of all rational means of ascer taining truth (Trammel v. United States, 445 U.S. 40, 100 S. Ct. 906, 63 L. Ed. 2d 186 [1980]). Yet courts view certain interests and relationships to be of such importance that they protect those interests and relationships from certain efforts to gather evidence. These protections, or exclusions from the general rule of free access to evidence, are known as privileges.

Federal courts recognize several types of privileges. To encourage clients to communicate freely with their lawyers and to fully disclose any information that may enable their lawyers to provide appropriate legal advice, courts allow clients to refuse to disclose and to prevent any other person from disclosing confidential communications made when seeking legal services. This privilege applies to clients' communications with their attorneys and with the attorneys' office staff. It protects only confidential communications, not communications made to friends or acquaintances in addition to an attorney.

The attorney-client privilege applies to the client, not the attorney. Thus, the client, but not the attorney, has the right to waive the privilege and to testify regarding protected communications. The privilege does not terminate even when the attorney-client relationship does. The privilege does not apply to a client's allegations of a breach of duty by the attorney.

To promote open communication within marital relationships, the rules of evidence also recognize a marital privilege. In criminal cases, a person has the privilege to refuse to testify against a spouse. This privilege covers only evidentiary matters that would incriminate the non-testifying spouse (i.e., the defendant), as other matters are not likely to jeopardize the marriage relationship. The non-testifying spouse does not have the right to assert the privilege; the privilege belongs only to the testifying spouse.

In criminal and civil cases, testimony about any confidential communications between spouses is also afforded a privilege. Either spouse, not just the testifying spouse, may assert this privilege. Unlike the testifying-spouse privilege, the confidential-marital-communications privilege survives the termination of the marriage by death or divorce, but it does not apply to permanently separated spouses.

Courts also recognize a political-vote privilege, a clergy-penitent privilege, and qualified privileges for trade secrets, state secrets, and the identity of an informant. Some courts also recognize a physician-patient privilege, an accountant-client privilege, and a privilege granted to journalists seeking to protect their news sources.

Past Bad Acts

Generally, evidence of past bad acts by a criminal defendant is not admissible to prove that the defendant is a bad person and therefore committed the crime charged. However, evidence of past bad acts will be admitted for other purposes such as to show motive, intent, preparation, plan, knowledge, identity, or absence of a mistake or accident. Such evidence is also admissible for impeachment purposes, (for example, if a defendant takes the stand) and when a defendant seeks to introduce the evidence in his or her defense.

In Ohler v. United States, 529 U.S. 753, 120 S.Ct. 1851, 146 L.Ed.2d 826 (U.S.Cal., May 22, 2000) (NO. 98-9828), the defendant Ohler was tried for importation of marijuana and possession of marijuana with the intent to distribute. After the trial court granted the government's motion to admit evidence of her previous conviction for methamphetamine possession, as impeachment evidence under Federal Rule of Evidence 609(a)(1), Ohler decided to bring out her prior conviction under direct examination, in order to "remove the sting" from the prosecutor's possible elicitation of the conviction on cross-examination. (Under the trial court's ruling, the prior conviction was only admissible in the event that Ohler testified.) The jury convicted Ohler on both counts, and she appealed, claiming that the trial court erred in admitting her prior conviction. The U.S. Court of Appeals for the Ninth Circuit and the United States Supreme Court affirmed her conviction, holding that Ohler had waived her objection to the evidence by introducing it herself.

Further Readings

Gillmor, Barron, and Terry Simon. 1990. Mass Communication Law Cases and Comment. 5th ed. St. Paul, Minn.: West.

Leonard, David P. 1995. "Foreword: Twenty Years of the Federal Rules of Evidence." Loyola of Los Angeles Law Review 28 (June).

Mauet, Thomas A. 1988. Fundamentals of Trial Techniques. 2d ed. Boston: Little, Brown.

McCormick on Evidence. 1984 and Supp. 1987. 3d ed. St. Paul, Minn.: West.

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