What Is the Burden of Proof? Deciding Who Has to Make the Case

In any dispute where the evidence does not settle the question, the party bearing the burden fails. That makes the allocation decisive in exactly the cases that are genuinely difficult, which is most of them. The general principle is that whoever asserts something must support it, expressed in the legal maxim that proof lies on the person who asserts rather than on the person who denies, and the practical rationale is that proving a negative is frequently impossible while proving a positive requires only producing the evidence you presumably have. That is why the presumption of innocence places the burden on the prosecution, and why the alternative arrangement, requiring a defendant to demonstrate innocence, is regarded as unacceptable rather than merely inconvenient. The same reasoning applies outside law, so a person claiming that an unusual thing exists must make the case, and a person who is unconvinced need not disprove it, which is the structure behind the widely quoted principle that extraordinary claims require extraordinary evidence.

Bearing a burden means meeting a standard, and the standards differ substantially by context:

• •Beyond reasonable doubt, the criminal standard, deliberately demanding because convicting an innocent person is regarded as far worse than acquitting a guilty one
• •The balance of probabilities, the civil standard, requiring only that a claim be more likely than not, which is why the same facts can produce different outcomes in criminal and civil proceedings
• •Clear and convincing evidence, an intermediate standard used in some jurisdictions for particular matters
• •Reasonable suspicion and probable cause, lower thresholds governing investigative powers rather than final determinations
• •Prima facie, meaning enough evidence to require an answer, which shifts a burden to the other party rather than deciding anything
• •Scientific conventions including significance thresholds, which serve a comparable function by specifying how much evidence counts as enough before a claim is provisionally accepted

Burdens move during a dispute in legitimate ways and are shifted illegitimately in argument. Legally, an evidential burden can pass to a defendant who raises a specific defence, and certain statutory provisions reverse the burden explicitly, which is controversial and subject to challenge under human rights law. In ordinary argument the commonest abuse is asserting a claim and then demanding that the other party disprove it, which reverses the allocation without justification and is sometimes called shifting the burden. Related moves include the argument from ignorance, which treats the absence of disproof as proof, and the loaded question, which presupposes a contested claim so that any answer concedes it. A subtler problem arises when both parties assert something, since each then bears a burden, and disputes frequently proceed with each side demanding that the other go first. The usual resolution is that the party departing from the default position, whatever that is in the context, argues first.

Many real disputes are arguments about what the default should be rather than about the evidence, and recognising that clarifies them. Regulatory debates turn on whether a substance or technology must be shown safe before use or shown harmful before restriction, which is the core of the precautionary principle and which reverses the burden in a way its critics regard as paralysing and its supporters as prudent. Planning disputes turn on whether development is permitted unless objections succeed or forbidden unless a case is made. Medical decisions turn on whether an intervention must be justified or a refusal must be. Public policy arguments about liberty and restriction are frequently disputes about which party must justify themselves. In each case appealing to evidence will not settle the matter, since both sides may agree about the facts and disagree about who must act in the face of uncertainty, and the honest form of the argument states that openly rather than dressing it as a factual dispute.

Whoever bears the burden loses when the evidence is inconclusive, which makes the allocation decisive in exactly the hard cases. The default places it on whoever asserts, because proving a negative is usually impossible, which is why the prosecution must prove guilt. Standards differ, so the same facts can fail a criminal case and succeed in a civil one. Many real disputes are arguments about the default rather than about evidence.