In criminal law, Blackstone's ratio (also known as Blackstone's formulation) is the idea that:
as expressed by the English jurist William Blackstone in his seminal work Commentaries on the Laws of England, published in the 1760s.
The idea subsequently became a staple of legal thinking in Anglo-Saxon jurisdictions and continues to be a topic of debate. There is also a long pre-history of similar sentiments going back centuries in a variety of legal traditions. The message that government and the courts must err on the side of bringing in verdicts of innocence has remained constant.
In Blackstone's Commentaries
The phrase, repeated widely and usually in isolation, comes from a longer passage, the fourth in a series of five discussions of policy by Blackstone:
The phrase was absorbed by the British legal system, becoming a maxim by the early 19th century. It was also absorbed into American common law, cited repeatedly by that country's Founding Fathers, later becoming a standard drilled into law students all the way into the 21st century.
Other commentators have echoed the principle. Benjamin Franklin stated it as: "it is better 100 guilty Persons should escape than that one innocent Person should suffer".
Defending British soldiers charged with murder for their role in the Boston Massacre, John Adams also expanded upon the rationale behind Blackstone's Ratio when he stated: We find, in the rules laid down by the greatest English Judges, who have been the brightest of mankind; We are to look upon it as more beneficial, that many guilty persons should escape unpunished, than one innocent person should suffer. The reason is, because it’s of more importance to community, that innocence should be protected, than it is, that guilt should be punished; for guilt and crimes are so frequent in the world, that all of them cannot be punished; and many times they happen in such a manner, that it is not of much consequence to the public, whether they are punished or not. But when innocence itself, is brought to the bar and condemned, especially to die, the subject will exclaim, it is immaterial to me, whether I behave well or ill; for virtue itself, is no security. And if such a sentiment as this, should take place in the mind of the subject, there would be an end to all security what so ever. Given that Sir Matthew Hale and Sir John Fortescue in English law had made similar statements previously, some kind of explanation is required for the enormous popularity and influence of the phrase across all the Anglo-Saxon legal systems. Cullerne Bown has argued that it "...can be seen as a new kind of buttress of the law that was required in a new kind of society."
Historic expressions of the principle
The immediate precursors of Blackstone's ratio in English law were articulations by Hale (about 100 years earlier) and Fortescue (about 200 years before that), both influential jurists in their time. Hale wrote: "for it is better five guilty persons should escape unpunished, than one innocent person should die." Fortescue's De Laudibus Legum Angliae (c. 1470) states that "one would much rather that twenty guilty persons should escape the punishment of death, than that one innocent person should be condemned and suffer capitally."
Some 300 years before Fortescue, the Jewish legal theorist Maimonides wrote that "the Exalted One has shut this door" against the use of presumptive evidence, for "it is better and more satisfactory to acquit a thousand guilty persons than to put a single innocent one to death."
Maimonides argued that executing an accused criminal on anything less than absolute certainty would progressively lead to convictions merely "according to the judge's caprice" and was expounding on both Exodus 23:7 ("do not bring death on those who are innocent and in the right") and an Islamic text, the Jami' al-Tirmidhi.
Islamic scholar Al-Tirmidhi quotes the Prophet Muhammad as saying, "Avoid legal punishments as far as possible, and if there are any doubts in the case then use them, for it is better for a judge to err towards leniency than towards punishment". Another similar expression reads, "Invoke doubtfulness in evidence during prosecution to avoid legal punishments".
Other statements, some even older, which seem to express similar sentiments have been compiled by Alexander Volokh. A vaguely similar principle, echoing the number ten and the idea that it would be preferable that many guilty people escape consequences than a few innocents suffer them, appears as early as the narrative of the Cities of the Plain in Genesis (at 18:23–32),
