Blackstone's Ratio is a foundational principle of criminal justice articulated by the English jurist Sir William Blackstone in his Commentaries on the Laws of England (1765–1769), where he wrote that "it is better that ten guilty persons escape than that one innocent suffer." The formulation captures an asymmetric preference in legal systems: false convictions are treated as a graver moral and institutional harm than false acquittals.
The idea predates Blackstone. Similar ratios appear in the writings of Matthew Hale, John Fortescue (15th century), and even further back in Jewish and Roman legal commentary, though the specific 10:1 figure is now associated with Blackstone. The principle was cited approvingly by Benjamin Franklin, who in a 1785 letter wrote that it is better "100 guilty Persons should escape than that one innocent Person should suffer."
In modern jurisprudence, Blackstone's Ratio underpins several procedural protections, including:
- The presumption of innocence.
- The "beyond a reasonable doubt" standard in criminal trials.
- Exclusionary rules on improperly obtained evidence.
- Due process guarantees, such as those in the Fifth and Fourteenth Amendments to the U.S. Constitution and Article 6 of the European Convention on Human Rights.
The U.S. Supreme Court invoked the ratio in In re Winship (1970), which formalised the reasonable-doubt standard, and again in Coffin v. United States (1895), which articulated the presumption of innocence. Justice John Harlan's concurrence in Winship explicitly cited the Blackstone formulation.
Critics, including legal scholars such as Daniel Epps, have questioned whether the ratio's strong tilt toward acquittal is always socially optimal, particularly in contexts involving violent recidivism or mass atrocity prosecution. Debates over counterterrorism detention, sexual assault evidentiary standards, and international criminal tribunals frequently invoke or contest the ratio when balancing protection of the innocent against accountability for the guilty.
Example
In *In re Winship* (1970), the U.S. Supreme Court drew on Blackstone's Ratio to hold that the reasonable-doubt standard is constitutionally required in juvenile delinquency proceedings.
Frequently asked questions
Sir William Blackstone formulated the 10:1 version in his Commentaries on the Laws of England (1765–69), though analogous ideas appear in earlier writers including John Fortescue and Matthew Hale.
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