Evidence (law)

Evidence law—often called the rules of evidence—sets the guidelines for how facts are proven in court. It decides what a judge (in a bench trial) or a jury (in a jury trial) can or cannot consider when making a decision. The law also addresses how much evidence is needed, how reliable it must be, and what type of proof is required to win a case. These rules shift depending on whether the case is in criminal, civil, or family court, and they differ from one jurisdiction to another.

The amount of evidence required is known as the quantum, while the quality refers to how trustworthy that evidence is considered. Key rules governing what evidence is allowed include those on hearsay, authentication, relevance, privilege, witnesses, opinions, expert testimony, identification, and physical evidence. Standards of evidence—such as reasonable suspicion, preponderance of the evidence, clear and convincing evidence, or beyond a reasonable doubt—indicate how strong the proof must be to meet the legal burden in a given situation.

Evidence comes in several forms or from different sources. It covers testimony (like oral statements or written affidavits), exhibits (physical objects), documentary material, and demonstrative evidence. These are admissible—meaning the judge or jury can consider them—in a judicial or administrative proceeding, such as a court of law.

When a dispute, civil or criminal, goes to court, one party usually has to prove certain issues to persuade the court to rule in their favor. The law sets guidelines to ensure that evidence presented is trustworthy.

**History**

**Ancient and medieval law** Hammurabi’s Code included rules requiring oaths and witnesses, as seen in laws 10, 11, and 12. The Old Testament demanded at least two witnesses to convict someone of a crime. Ancient Roman law gave judges freedom to evaluate evidence but insisted that proof falls on the party affirming a fact, not the one denying it, and that no one should be convicted on suspicion alone. Medieval Roman law developed a detailed grading of evidence. Building on the Biblical two-witness rule, it held that a single witness or private documents could count as half-proof—not enough for conviction but enough to justify torture to get more evidence. Because judges, not juries, evaluated evidence in the continental (civil law) system, it did not develop the exclusionary rules found in English law.

**Anglophone (Common) law** A key feature of English common law was the jury as finder of fact, while the judge handled the law. Modern jury trials in the 16th and 17th centuries required rules to regulate what testimony and evidence could be presented to the jury. Early common law evidence rules came from judicial decisions, but Parliament also acted. In 1677, the Statute of Frauds and Perjuries barred plaintiffs from alleging certain contract breaches to the jury without a signed, written document. Another early rule banned hearsay—using an out-of-court statement to prove the truth of what it says. In the early 19th century, Chief Justice Lord Mansfield of the Court of Common Pleas noted that in Scotland and most continental states, judges decide both facts and law, so they can safely hear hearsay evidence and disregard it or give it little weight. But in England, where juries alone judge facts, hearsay was excluded because no one could predict its effect on their minds. Hearsay rules have been updated many times since. In England and Wales, the Civil Evidence Act 1995, section 1, now allows hearsay evidence in civil cases; legislation also permits it in criminal proceedings, which can let accusers bring in friends or family to give false evidence, since it would normally be rejected by the judge. Some presiding authorities are not bound by evidence rules, such as U.S. military tribunals and Australian tribunals that try health professionals.

**Relevance and social policy** In every jurisdiction based on English common law, evidence must follow several rules to be admissible. It must be relevant—aimed at proving or disproving a legal element. But relevance is usually necessary, not sufficient, for admissibility. Relevant evidence can be excluded if it is unfairly prejudicial or confusing. The relevance or irrelevance of evidence cannot be determined by logical analysis alone. There is general agreement that assessing relevance involves judgments about probabilities or uncertainties. Beyond that, little agreement exists. Many legal scholars and judges believe ordinary reasoning, or common sense, plays a key role. There is less agreement on whether anything else is involved.