Burden of proof
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- This article is on the legal definition of the term. For the philosophical use, see Burden of proof (logical fallacy).
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 their claim. For example the presumption of innocence places a legal burden upon the prosecution to prove all elements of the offence and to disprove all the defences.
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 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 US, beyond a reasonable doubt (commonly referred to as BARD), or just beyond reasonable doubt. In addition to these, the US introduced a third standard called clear and convincing evidence.
 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.
 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 US civil procedure. In order 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 all but 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 in most criminal cases. This means that the proposition must be proven to the extent that there is no "reasonable doubt" in the mind of a reasonable person (usually this means the mind of the judge or jury). There can still be a doubt, but only to the extent that it would be "unreasonable" to assume the falsity of the proposition. 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."
The difference between the criminal and civil standards of proof has raised some interesting cases. For example, O.J. Simpson was cleared in a criminal trial of murder, but, in a subsequent civil trial, due to the lower standard of proof, had substantial damages for wrongful death ordered against him.
 Legal uses
In jurisprudence, the burden of proof is the concept of holding one party to a dispute or one side of a debate responsible for producing a prima facie case. If this party fails to produce a valid case, the decision will go against them, without requiring any further evidence or discussion.
Burden of proof is one of the most important issues in litigation, and in criminal cases it is closely linked with the presumption of innocence - the principle in most modern legal systems that an accused person is "innocent until proven guilty".
The burden, therefore, initially lies with the plaintiffs in a case, and not on a defendant who would need to prove that something did not happen. Adequate evidence can, however, shift the burden of proof to the other party.
 Criminal law
In criminal cases, the burden of proof is often on the prosecutor. 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 innocent if a valid case is not presented.
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
- 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 a murderer
In practice, the question of who has burden of proof usually does not change the outcome of a case, because prosecutors rarely bring cases which are marginal enough so that who has burden of proof makes a difference. In any case, most criminal cases in the United States are resolved via plea bargaining in which burden of proof again does not make a significant difference to the outcome of the case.
 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 person's responsibility who is making the bold claim to prove it.
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 beliefs about thermodynamics.
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 humourous 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'.