Proof beyond a reasonable doubt is the highest level of proof demanded in American courts. It is the usual standard for criminal cases, and in criminal litigation it has constitutional grounding in decisions of the United States Supreme Court. Although the reasonable doubt standard is not often used in noncriminal settings, there are exceptional situations, usually where liberty is placed in jeopardy, when a jurisdiction will borrow the criminal standard of proof for a civil case.
Any standard of proof chosen by an American court recognizes that in all litigation there is the chance of a mistake. If opposing litigants agree on the various matters that constitute their case, usually the case is settled. There is little for a judge or a jury to do. Once a dispute arises, however, adversaries offer conflicting evidence and conflicting interpretations of evidence to decision makers. Rarely, if ever, is there a dispute in which every witness and every aspect of physical and scientific evidence presented by opposing parties point with perfect certainty to one specific conclusion. Witnesses may suffer from ordinary human frailties—they have memory problems; they sometimes confuse facts; they see events differently from each other; they have biases and prejudices that call into question their judgment; and they may be frightened and have trouble communicating on the witness stand. Physical evidence might be damaged or destroyed and thus of minimal or no use at trial. Or, it might be difficult to connect physical evidence with the parties before the court. Even scientific tests often provide little more than probabilities concerning the relationship of evidence to the issues in a case.
Were judges and juries required to decide cases on the basis of absolute certainty about what occurred, it is doubtful that they ever would find the standard satisfied. Whoever was required to prove the case would always lose. Recognizing that absolute certainty is not reasonably possible, American courts have chosen to demand less. How much less determines the extent to which they are willing to accept the risk of error in the course of litigation.
In criminal cases the typical requirement is that the government must prove the essential elements of any offense it chooses to charge beyond a reasonable doubt. This means that, although the decision maker need not be certain that a defendant is guilty before convicting, any reasonable doubt requires that it find the defendant not guilty. Such a standard allocates most of the risk of error in criminal cases to the state. It cannot assure that no innocent person will ever be convicted, but the standard is demanding enough to make it most unlikely that someone who is actually innocent will be found guilty. It is more likely that truly guilty persons may go free, but that is the price American criminal justice pays to avoid mistakes that harm the innocent.
It is uncertain when this standard of proof was first used in criminal cases. In early England, whether or not a person would be convicted depended on his ability to produce compurgators or to avoid misfortune in an ordeal. Subsequently, success turned on whether or not a suspect could succeed in trial by combat. As trial by jury replaced other forms of proof, the jurors originally decided cases on the basis of their own knowledge, and even if they relied on informants, the jurors themselves were responsible for the accuracy of the facts. Not until the notion of an independent fact finder, typically a jury, developed was a standard of proof very meaningful. With the development of the independent and neutral fact finder, the "beyond a reasonable doubt" concept took on importance.
Although there is no mention of the proof beyond a reasonable doubt concept in the United States Constitution, trial by jury is in all but petty cases guaranteed by the Sixth Amendment, and with the Supreme Court's decision in duncan v. louisiana (1968), this right is now binding on the states. By the time the Sixth Amendment was adopted, proof beyond a reasonable doubt was closely associated with the right to an impartial jury guaranteed by the Constitution in criminal cases.
Thus, it is not surprising that the Supreme Court has found the proof beyond a reasonable doubt standard to be constitutionally required in criminal cases with respect to all essential elements of offenses charged, whether the criminal case is litigated in state or federal court (in re winship, 1970). The Court associated the high proof standard with the strong presumption of innocence in criminal cases and observed that before a defendant may be stigmatized by criminal conviction and punished for criminal wrongdoing, due process requires the state to prove guilt beyond a reasonable doubt. (See Jackson v. Virginia, 1979.)
There is little agreement on exactly what a reasonable doubt is. No single definition of reasonable doubt has ever gained acceptance in American courts. There does seem to be some consensus that a decision maker should understand that a reasonable doubt is one based in reason as applied to the proof offered in a case. This elaboration of the standard is consistent with the oath that judges administer to jurors who are called upon to decide a case. Beyond this, it is difficult to define the term. Any language that is used is likely to be challenged as being either too demanding or not demanding enough.
Judges and juries have come to know that the proof beyond a reasonable doubt standard represents American regard for liberty and the dignity of the individual who stands against the state and who seeks to preserve his freedom and independence. A reasonable doubt will protect him.
Stephen A. Saltzburg
(see also: Burden of Proof.)
Kalven, Harry, Jr. and Zeisel, Hans 1966 The American Jury. Boston: Little, Brown.
Tribe, Laurence H. 1971 Trial by Mathematics: Precision and Ritual in the Legal Process. Harvard Law Review 84:1329–1393.