Blackstone's ratio
Blackstone’s ratio is the idea that it is better for ten guilty people to go free than for one innocent person to suffer. It comes from William Blackstone’s 1760s work, Commentaries on the Laws of England, where he urged caution in convicting—arguing that it is safer for the public if innocence is protected, even if some guilty people escape punishment.
Long before Blackstone, other legal thinkers urged similar cautions. Sir Matthew Hale and, even earlier, John Fortescue argued that it’s better to err on the side of letting someone guilty go than punishing an innocent. Similar sentiments appear in other traditions too, including writings by Maimonides and, later, in various religious and philosophical texts. In the American and British legal traditions, the phrase was adopted as a guiding maxim by the 19th century and became a familiar part of legal training.
In the United States, many state courts have adopted versions of the ratio, sometimes using numbers other than ten. The idea influenced debates about what counts as proof beyond a reasonable doubt, and it has been cited by famous figures such as Benjamin Franklin and John Adams to explain why protecting the innocent matters more than punishing the guilty. The principle has also shown up in discussions about how much evidence is needed to convict and in arguments about the fairness of the criminal justice system.
In modern discussions, scholars often connect Blackstone’s ratio to the probability standard in criminal trials. Some interpret it as implying a high threshold of certainty—roughly around 90% certainty of guilt, if you translate the idea into a numerical standard. Research on juries suggests that when numbers or probabilities are stated explicitly, jurors’ verdicts can become more consistent. Some scholars have even proposed turning the ratio into formal jury instructions that set a clear probability goal for guilty verdicts.
Over time, the ratio has faced criticism. Its mathematical foundation is not airtight, and as scientific understanding of evidence and probability has advanced, the idea’s authority has waned. Modern theories, including legal models that balance rights and public safety, have taken its place in guiding how trials should work. Nevertheless, the ratio helped shape the broader principle that the justice system should be cautious about convicting and should prioritize protecting the innocent.
The ratio has also been invoked in controversial ways. Some leaders and thinkers have used a version of “better many guilty go free than one innocent suffer” to justify harsh or irreversible actions, a stance that has sparked strong opposition when used to defend harsh treatment or executions. The key question it raises—how to balance the risk of punishing the innocent against the need to punish the guilty—remains at the heart of debates about due process, proof, and the proper limits of state power.
In short, Blackstone’s ratio is a longstanding, influential idea about putting a high premium on innocence in criminal prosecutions. While its exact numerical meaning has faded in modern practice, its core message—protect the innocent, even if some guilty go free—continues to shape debates about how we prove guilt and how we run fair trials.
This page was last edited on 3 February 2026, at 07:52 (CET).