Burden of proof

For Burden of Proof use in Rhetoric see: Burden of proof (rhetoric)

In the common law, burden of proof is the obligation to prove allegations which are presented in a legal action. More colloquially, burden of proof refers to an obligation in a particular context to defend a position against a prima facie other position.

Types of burden
There are generally three broad types of burdens.

A legal burden or a burden of persuasion is an obligation that remains on a single party for the duration of the claim. Once the burden has been entirely discharged to the satisfaction of the trier of fact, the party carrying the burden will succeed in its claim. For example, the presumption of innocence places a legal burden upon the prosecution to prove all elements of the offence (generally beyond a reasonable doubt) and to disprove all the defences except for affirmative defenses in which the proof of nonexistence of all affirmative defence(s) is not constitutionally required of the prosecution (432 U.S. 197).

An evidentiary burden or burden of leading evidence is an obligation that shifts between parties over the course of the hearing or trial. A party may submit evidence that the court will consider prima facie proof of some state of affairs. This creates an evidentiary burden upon the opposing party to present evidence to refute the presumption.

A tactical burden is an obligation similar to an evidentiary burden. Presented with certain evidence, the Court has the discretion to infer a fact from it unless the opposing party can present evidence to the contrary.

Standard of proof
The standard of proof is the level of proof required in a legal action to discharge the burden of proof, ie convince the court that a given proposition is true. The degree of proof required depends on the circumstances of the proposition. Typically, most countries have two levels of proof: the balance of probabilities (BOP), called the preponderance of evidence in the U.S., (which is the lowest level, generally thought to be greater than 50%, although numeric approximations are controversial) and beyond a reasonable doubt (which is the highest level, but defies numeric approximation). In addition to these, the U.S. introduced a third standard called clear and convincing evidence, (which is the medium level of proof).

The first attempt to quantify reasonable doubt was made by Simon in 1970. In the attempt, she presented a trial to groups of students. Half of the students decided the guilt or innocence of the defendant. The other half recorded their perceived likelihood, given as a percentage, that the defendant committed the crime. She then matched the highest likelihoods of guilt with the guilty verdicts and the lowest likelihoods of guilt with the innocent verdicts. From this, she gauged that the cutoff for reasonable doubt fell somewhere between the highest likelihood of guilt matched to an innocent verdict and the lowest likelihood of guilt matched to a guilty verdict. From these samples, Simon concluded that the standard was between .70 and .74.

Air of reality
The "air of reality" is a standard of proof used to determine whether a criminal defense may be used. The test asks whether a defense can be successful if it is assumed that all the claimed facts are to be true.

Reasonable suspicion
Reasonable suspicion is a low standard of proof in the U.S. to determine whether a brief investigative stop or a brief search by a police officer or any government agent is warranted. In Terry v. Ohio,, the United States Supreme Court ruled that reasonable suspicion requires specific, articulable, and individualized suspicion that crime is afoot. A mere guess or "hunch" is not enough to constitute reasonable suspicion. As a result of the low threshold, the extent of intrusiveness of the search and/or seizure allowed is lower than the extent of intrusiveness allowed when a government agent has probable cause to suspect that evidence of a crime will be found.

A good illustration of this is the continuum of a typical police/citizen interaction:

Consensual encounter between officer and citizen (no level of suspicion required) →a stop initiated by the officer that would cause a reasonable person to feel that he/she is not free to leave (reasonable suspicion required) →arrest (probable cause required).

Probable Cause
Probable cause is a relatively low standard of proof, which is used in the United States to determine whether a search, or an arrest, is warranted. It is also used by grand juries to determine whether to issue an indictment. In the civil context, this standard is often used where plaintiffs are seeking a prejudgment remedy.

In the criminal context, the U.S. Supreme Court in United States v. Sokolow,, determined that probable cause requires "a fair probability that contraband or evidence of a crime will be found." Courts vary when determining what constitutes a "fair probability," some say 30%, others 40%, others 51%.

Balance of probabilities
Also known as the "preponderance of evidence", this is the standard required in most civil cases. The standard is met if the proposition is more likely to be true than not true. Effectively, the standard is satisfied if there is greater than 50% chance that the proposition is true. Lord Denning in Miller v. Minister of Pension described it simply as "more probable than not".

Clear and convincing evidence
Clear and convincing evidence is the intermediate level of burden of persuasion sometimes employed in the U.S. civil procedure. To prove something by "clear and convincing evidence", the party with the burden of proof must convince the trier of fact that it is substantially more likely than not that the thing is in fact true. This is a lesser requirement than "proof beyond a reasonable doubt", which requires that the trier of fact be close to certain of the truth of the matter asserted, but a stricter requirement than proof by "preponderance of the evidence," which merely requires that the matter asserted seem more likely true than not.

Beyond a reasonable doubt
This is the standard required by the prosecution in most criminal cases within an adversarial system. This means that the proposition being presented by the government must be proven to the extent that there is no "reasonable doubt" in the mind of a reasonable person that the defendant is guilty. There can still be a doubt, but only to the extent that it would not affect a "reasonable person's" belief that the defendant is guilty. If the doubt that is raised does affect a "reasonable person's" belief that the defendant is guilty, the jury is not satisfied beyond a "reasonable doubt". The precise meaning of words such as "reasonable" and "doubt" are usually defined within jurisprudence of the applicable country. In the United States, it is usually reversible error to instruct a jury that they should find guilt on a certain percentage of certainty (such as 90% certain). Usually, reasonable doubt is defined as "any doubt which would make a reasonable person hesitate in the most important of his or her affairs."

Criminal law
In criminal cases, the burden of proof is often on the prosecutor - sometimes referred to by the latin legal expression "ei incumbit probatio qui dicit, non que negat" (the burden of proof rests on who asserts, not on who denies). The principle that it should be is known as the presumption of innocence, but is not upheld in all legal systems or jurisdictions. Where it is upheld, the accused will be found not guilty if this burden of proof is not sufficiently carried by the prosecution.

For example, if the defendant (D) is charged with murder, the prosecutor (P) bears the burden of proof to show the jury that D did murder someone.


 * Burden of proof: P
 * Burden of production: P has to show some evidence that D had committed murder
 * e.g. witness, forensic evidence, autopsy report
 * Failure to meet the burden: the issue will be decided as a matter of law (the judge makes the decision), in this case, D is presumed innocent
 * Burden of persuasion: if at the close of evidence, the jury cannot decide if P has established with relevant level of certainty that D had committed murder, the jury must find D not guilty of the crime of murder
 * Measure of proof: P has to prove every element of the offence beyond a reasonable doubt, but not necessarily prove every single fact beyond a reasonable doubt.

Civil law
In civil law cases, the "burden of proof" requires the plaintiff to convince the trier of fact (whether judge or jury) of the plaintiff's entitlement to the relief sought. This means that the plaintiff must prove each element of the claim, or cause of action, in order to recover.

The burden of proof must be distinguished from the "burden of going forward," which simply refers to the sequence of proof, as between the plaintiff and defendant. The two concepts are often confused.

Science and other uses
Outside a legal context, "burden of proof" means that someone suggesting a new theory or stating a claim must provide evidence to support it: it is not sufficient to say "you can't disprove this." Specifically, when anyone is making a bold claim, it is not someone else's responsibility to disprove the claim, but is rather the responsibility of the person who is making the bold claim to prove it. In short, X is not proven simply because "not X" cannot be proven (see negative proof).

Taken more generally, the standard of proof demanded to establish any particular conclusion varies with the subject under discussion. Just as there is a difference between the standard required for a criminal conviction and in a civil case, so there are different standards of proof applied in many other areas of life.

The less reasonable a statement seems, the more proof it requires. The scientific consensus on cold fusion is a good example. The majority believes this can not really work, because believing that it would do so would force the alteration of a great many other tested and generally accepted theories about nuclear physics.

A classic example comes from Criswell's final speech at the end of Ed Wood's Plan 9 from Outer Space: "My friends, you have seen this incident, based on sworn testimony. Can you prove that it didn't happen?". Considering that the incident in question involved grave robbers from space, the burden of proof is being incorrectly assigned.

A humorous example comes from the television series Futurama during the opening credit gag for the episode Obsoletely Fabulous states regarding the premise of the show; 'You can't prove it won't happen'.