498 U.S. 39 (1990)
Petitioner was convicted in a Louisiana trial court of first-degree murder and was sentenced to death.1 He appealed to the Supreme Court of Louisiana.2 He argued that the reasonable-doubt instruction used in the guilt phase of his trial was constitutionally defective.3
The instruction provided in relevant part: “If you entertain a reasonable doubt as to any fact or element necessary to constitute the defendant’s guilt, it is your duty to give him the benefit of that doubt and return a verdict of not guilty. Even where the evidence demonstrates a probability of guilt, if it does not establish such guilt beyond a reasonable doubt, you must acquit the accused. This doubt, however, must be a reasonable one; that is one that is founded upon a real tangible substantial basis and not upon mere caprice and conjecture. It must be such doubt as would give rise to a grave uncertainty, raised in your mind by reasons of the unsatisfactory character of the evidence or lack thereof. A reasonable doubt is not a mere possible doubt. It is an actual substantial doubt. It is a doubt that a reasonable man can seriously entertain. What is required is not an absolute or mathematical certainty, but a moral certainty.”4
The Supreme Court of Louisiana rejected petitioner’s argument.5 The court observed that the use of the phrases “grave uncertainty” and “moral certainty” in the instruction, if taken out of context, might overstate the requisite degree of uncertainty and confuse the jury.6 But taking the charge as a whole, the court concluded that reasonable persons of ordinary intelligence would understand the definition of “reasonable doubt.”7
The United States Supreme Court granted the motion of petitioner for leave to proceed in forma pauperis and the petition for a writ of certiorari.8
Whether the reasonable doubt instruction in this case complied with Winship?9
In state criminal trials, the Due Process Clause of the Fourteenth Amendment protects the accused against conviction except upon proof beyond a reasonable doubt of every fact necessary to constitute the crime with which he is charged.10 This reasonable-doubt standard plays a vital role in the American scheme of criminal procedure.11 It is a prime instrument for reducing the risk of convictions resting on factual error.12 In construing the instruction, we consider how reasonable jurors could have understood the charge as a whole.13
No. The instruction equated a reasonable doubt with a grave uncertainty and an actual substantial doubt.14 It stated that what was required was a moral certainty that the defendant was guilty.15 The words substantial and grave, as they are commonly understood, suggest a higher degree of doubt than is required for acquittal under the reasonable-doubt standard.16 When those statements are then considered with the reference to moral certainty, rather than evidentiary certainty.17
It becomes clear that a reasonable juror could have interpreted the instruction to allow a finding of guilt based on a degree of proof below that required by the Due Process Clause.18
The reasonable doubt instruction in this case did not comply with Winship, so the judgment of the Supreme Court of Louisiana is reversed and the case is remanded for further proceedings not inconsistent with this opinion.19