Evidence, broadly construed, is anything presented in support of an assertion. This support might be strong or weak. The strongest type of evidence is that which provides direct proof of the truth of an assertion. At the additional extreme is evidence that's merely consistent with an assertion but doesn't rule out other, contradictory assertions, as in circumstantial evidence.

In law, rules of evidence govern the types of evidence that are admissible in a legal proceeding. Types of legal evidence include testimony, documentary evidence, and physical evidence. The parts of a legal case which aren't in controversy are known, in general, as the "facts of the case." Beyond any facts that are undisputed, a judge or jury is usually tasked with being a trier of fact for the additional issues of a case. Evidence and rules are used to decide questions of fact that are disputed, a few of which might be determined by the legal burden of proof relevant to the case. Evidence in certain cases (e.g. capital crimes) must be more compelling than in additional situations (e.g. minor civil disputes), which drastically affects the quality and quantity of evidence necessary to decide a case.

Scientific evidence consists of observations and experimental results that serve to support, refute, or modify a scientific hypothesis or theory, when collected and interpreted in accordance with the scientific method.

In philosophy, the study of evidence is closely tied to epistemology, which considers the nature of knowledge and how it can be acquired.

Burden of proof

The burden of proof is the obligation of a party in an argument or dispute to provide sufficient evidence to shift the additional party's or a third party's belief from their initial position. The burden of proof must be fulfilled by both establishing confirming evidence and negating oppositional evidence. Conclusions drawn from evidence might be subject to criticism based on a perceived failure to fulfil the burden of proof.

Two principal considerations are:

  1. On whom does the burden of proof rest?
  2. To what degree of certitude must the assertion be supported?

The latter question depends on the nature of the point under contention and determines the quantity and quality of evidence required to meet the burden of proof.

In a criminal trial in the United States, for example, the prosecution carries the burden of proof after the defendant is presumed innocent until proven guilty beyond a reasonable doubt. Similarly, in most civil procedures, the plaintiff carries the burden of proof and must convince a judge or jury that the preponderance of the evidence is on their side. Other legal standards of proof include "reasonable suspicion", "probable cause" (as for arrest), "prima facie evidence", "credible evidence", "substantial evidence", and "clear and convincing evidence".

In a philosophical debate, there's an implicit burden of proof on the party asserting a claim, after the default position is generally one of neutrality or unbelief. Each party in a debate will therefore carry the burden of proof for any assertion they make in the argument, although a few assertions might be granted by the additional party without further evidence. If the debate is set up as a resolution to be supported by one side and refuted by another, the overall burden of proof is on the side supporting the resolution.

Evidence in science

In scientific research evidence is accumulated through observations of phenomena that occur in the natural world, or which are created as experiments in a laboratory or additional controlled conditions. Scientific evidence usually goes towards supporting or rejecting a hypothesis.

One must always remember that the burden of proof is on the person making a contentious claim. Within science, this translates to the burden resting on presenters of a paper, in which the presenters argue for their specific findings. This paper is placed before a panel of judges where the presenter must defend the thesis against all challenges.

When evidence is contradictory to predicted expectations, the evidence and the ways of making it are often closely scrutinised (see experimenter's regress) and only at the end of this process is the hypothesis rejected: this can be referred to as 'refutation of the hypothesis'. The rules for evidence used by science are collected systematically in an attempt to avoid the bias inherent to anecdotal evidence.

Evidence in law

An FBI Evidence Response Team gathering evidence by dusting an area for fingerprints

Evidence forms the quite foundation of legal system, without which law would be subject to the whims of those with power.

In law, the production and presentation of evidence depends first on establishing on whom the burden of proof lies. Admissible evidence is that which a court receives and considers for the purposes of deciding a particular case. Two primary burden-of-proof considerations exist in law. The first is on whom the burden rests. In many, especially Western, courts, the burden of proof is placed on the prosecution in criminal cases and the plaintiff in civil cases. The second consideration is the degree of certitude proof must reach, depending on both the quantity and quality of evidence. These degrees are different for criminal and civil cases, the former requiring evidence beyond a reasonable doubt, the latter considering only which side has the preponderance of evidence, or whether the proposition is more likely true or false. The decision maker, often a jury, but at times a judge, decides whether the burden of proof has been fulfilled.

After deciding who'll carry the burden of proof, evidence is first gathered and then presented before the court:

Gathering evidence

In criminal investigation, rather than attempting to prove an abstract or hypothetical point, the evidence gatherers attempt to determine who's responsible for a criminal act. The focus of criminal evidence is to connect physical evidence and reports of witnesses to a specific person.

Evidence before the court

The path that physical evidence takes from the scene of a crime or the arrest of a suspect to the courtroom is called the chain of custody. In a criminal case, this path must be clearly documented or attested to by those who handled the evidence. If the chain of evidence is broken, a defendant might be able to persuade the judge to declare the evidence inadmissible.

Presenting evidence before the court differs from the gathering of evidence in important ways. Gathering evidence might take a large number of forms; presenting evidence that tend to prove or disprove the point at issue is strictly governed by rules. Failure to follow these rules leads to any number of consequences. In law, certain policies allow (or require) evidence to be excluded from consideration based either on indicia relating to reliability, or broader social concerns. Testimony (which tells) and exhibits (which show) are the two main categories of evidence presented at a trial or hearing. In the United States, evidence in federal court is admitted or excluded under the Federal Rules of Evidence.

Types of evidence