Proof beyond a Reasonable Doubt

Under the due process clause of the Fifth Amendment, no individual may be convicted of a crime unless the prosecution can prove his guilt beyond a reasonable doubt. That standard is designed to reduce the possibility of false conviction by requiring jurors to acquit whenever there is reasonable doubt of the defendant’s guilt, no matter how strong the prosecution’s proof might otherwise be. The standard thus represents, as Justice Harlan wrote in the seminal case, In re Winship (397 U.S. 358, 1970), the ‘‘fundamental value determination of our society that it is far worse to convict an innocent man than to let a guilty man go free.’’

Although the Supreme Court has held that courts are constitutionally required to instruct jurors to apply the standard of proof beyond a reasonable doubt, it has never mandated a particular formulation of the standard. As a result, courts differ substantially in how they explain the prosecution’s burden of proof to jurors. Most attempt to differentiate between reasonable and unreasonable doubts, instructing jurors that a reasonable doubt is ‘‘something more than a guess or a surmise’’ or ‘‘a kind of doubt that would cause a reasonable and sensible person to hesitate before acting upon a matter of importance in his or her own affairs.’’ A minority of courts focus on how strong the prosecution’s case must be for the reasonable- doubt standard to be satisfied, instructing jurors that they need to be ‘‘firmly convinced’’ of the defendant’s guilt in order to convict. Finally, a few courts make no attempt to explain the standard at all, leaving it to jurors to apply the standard as they see fit.

Despite the Supreme Court’s reluctance to micromanage the reasonable-doubt standard, empirical research indicates that jurors interpret the government’s burden of proof very differently depending on the kind of instruction they receive. One study, for example, found that mock jurors presented with a weak murder case never convicted when given a ‘‘firmly convinced’’ instruction, but convicted nearly half the time when given an instruction that focused on the definition of reasonable doubt. Another study found that nearly one third of actual jurors who were given an instruction that did not explain the reasonabledoubt standard believed that the burden of proof was on the defendant to prove his innocence.

These studies are indicative of the fact that jurors generally underestimate how strong the prosecution’s case must be in order to satisfy the reasonable-doubt standard. The standard is the most restrictive in American law; judges generally agree that jurors should not convict unless they are at least 90 percent certain that the defendant is guilty. Nevertheless, jurors often set the threshold for proof beyond a reasonable doubt far lower, sometimes as low as 50 to 55 percent and rarely higher than 80 percent. Indeed, jurors often believe that the reasonable-doubt standard is no more demanding than the clear-andconvincing standard used in civil cases—the standard that the Supreme Court found inconsistent with the presumption of innocence in Winship.

KEVIN JON HELLER

References and Further Reading

  • Shapiro, Barabara J. Beyond Reasonable Doubt and Probable Cause: Historical Perspectives on the Anglo-American Law of Evidence. Berkeley: University of California Press, 1991.
  • Solum, Lawrence M., Refocusing the Burden of Proof in Criminal Cases: Some Doubt About Reasonable Doubt, Texas Law Review 78 (1999): 105–147.

Cases and Statutes Cited

  • In re Winship, 397 U.S. 358 (1970)

See also Due Process

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