This standard of proof is widely accepted in many criminal justice systems, and its origin can be traced to Blackstone's ratio, "It is better that ten guilty persons escape than that one innocent suffer."
Accordingly, the standard of proof forces the factfinder to ignore unreasonable doubts—doubts that are frivolous, hypothetical, or not logically linked to the evidence—and to consider evidence favoring the accused, since reasonable doubt entitles them to an acquittal.
[clarification needed] Therefore, jurisdictions using this standard often rely on additional or supplemental measures, such as a judge's specific instructions to a jury, to simplify or qualify reasonable doubt.
[8] Medieval Roman law, followed by the English jurist Edward Coke, expressed a similar idea by requiring "proofs clearer than light" for criminal conviction.
According to judicial law prior to the 1780s, "the Juryman who finds any other person guilty, is liable to the Vengeance of God upon his Family and Trade, Body and Soul, in this world and that to come.
This is the law as laid down in the Court of Criminal Appeal in Rex v. Davies 29 Times LR 350; 8 Cr App R 211, the headnote of which correctly states that where intent is an ingredient of a crime there is no onus on the defendant to prove that the act alleged was accidental.
[14][15] The leading decision is R. v. Lifchus,[15] where the Supreme Court discussed the proper elements of a charge to the jury on the concept of "reasonable doubt" and noted that "[t]he correct explanation of the requisite burden of proof is essential to ensure a fair criminal trial."
While the Court did not prescribe any specific wording that a trial judge must use to explain the concept, it recommended certain elements that should be included in a jury charge, as well as pointing out comments that should be avoided.
[20][21] The US Supreme Court held that "the Due Process clause protects the accused against conviction except upon proof beyond a reasonable doubt of every fact necessary to constitute the crime charged.
"[21] The US Supreme Court first discussed the term in Miles v. United States: "The evidence upon which a jury is justified in returning a verdict of guilty must be sufficient to produce a conviction of guilt, to the exclusion of all reasonable doubt.
[21] "[W]e explicitly hold that the Due Process Clause 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.
[25] Reasonable doubt came into existence in English common law and was intended to protect the jurors from committing a potentially mortal sin, since only God may pass judgment on man.