Blackstone's formulation

In criminal law, Blackstone's formulation (also known as Blackstone's ratio or the Blackstone ratio) is the principle that:

"It is better that ten guilty persons escape than that one innocent suffer",

...as expressed by the English jurist William Blackstone in his seminal work, Commentaries on the Laws of England, published in the 1760s.

Historically, the details of the ratio have varied, but the message that government and the courts must err on the side of innocence has remained constant.

The principle is much older than Blackstone's formulation, being closely tied to the presumption of innocence in criminal trials. An early example of the principle appears in the Bible (Genesis 18:23-32), as:

Abraham drew near, and said, "Will you consume the righteous with the wicked? What if there are fifty righteous within the city? Will you consume and not spare the place for the fifty righteous who are in it? ... What if ten are found there?" He [The Lord] said, "I will not destroy it for the ten's sake."

This was about the destruction of Sodom which, the Bible says, God did destroy after rescuing most of Lot's family.

27 Early the next morning Abraham got up and returned to the place where he had stood before the Lord. 28 He looked down toward Sodom and Gomorrah, toward all the land of the plain, and he saw dense smoke rising from the land, like smoke from a furnace.

29 So when God destroyed the cities of the plain, he remembered Abraham, and he brought Lot out of the catastrophe that overthrew the cities where Lot had lived.

Another example in the Islamic tradition, as compiled in the tome [Jami'] of at-Tirmidhi, quotes 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".

The 12th-century legal theorist Maimonides, expounding on this passage as well as Exodus 23:7 ("the innocent and righteous slay thou not") argued that executing an accused criminal on anything less than absolute certainty would progressively lead to convictions merely "according to the judge's caprice. Hence 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."

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Wikipedia