Perhaps because I have recently answered several questions on Zhihu regarding prosecutors and courts, I have been frequently invited to respond to inquiries about the “jury system,” such as “What are your thoughts on the jury system?” “What is the difference between the jury system and the prosecutorial system?” and “What are the pros and cons of the jury system?” After briefly scanning some highly upvoted answers, I noticed that many users with a scientific mindset directly applied mathematical probability calculations to conclude that “under the rule requiring unanimity for a verdict, as long as each individual is mentally sound, the collective outcome will be significantly more accurate than an individual’s judgment.” While such calculations serve as a useful attempt at popular science, helping ordinary people intuitively understand the operational logic of the jury system, they unfortunately overlook the unpredictability of human thought and behavior. Drawing conclusions from simple calculations can lead to significant deviations in real-life scenarios. Here, I will also briefly share my perspective on the jury system.

Why Pure Mathematical Calculations Are Unreliable

From a mathematical perspective, 12 jurors who are not entirely rational, each with an individual judgment accuracy of only 51%, would produce a collective verdict with approximately 58.2% accuracy under the unanimity rule, which is closer to the truth than the 51% accuracy of a single individual. If 12 jurors each had an 80% accuracy rate, the collective verdict under the unanimity rule would be correct about 99.9% of the time and incorrect only about 0.1%, demonstrating that the group’s unanimous outcome is superior to that of an individual. — A netizen’s response.

Such probability calculations are logically sound, as they are based on a clear, calculable model: individual judgments are independent, errors are randomly distributed, and the group only delivers a verdict when unanimity is achieved. Under these premises, the “wisdom of the crowd” can indeed filter out noise through consensus, bringing the outcome closer to the truth.

The problem is that real-world juries rarely meet these conditions.

Jurors are not independent “random variables” but highly socialized individuals. They are continuously influenced by the pace of the trial, lawyers’ rhetoric, the judge’s demeanor, media coverage, group pressure, and even differences in their identities. Judgment errors are not entirely random but often exhibit directional biases: sympathy, fear, anger, political leanings, and moral intuitions tend to amplify rather than cancel each other out within the group.

More importantly, a jury is not a pure “probability aggregator” but an institutional arrangement endowed with judicial authority. Mathematical models can only demonstrate that “under certain ideal conditions, a unanimous group judgment may be closer to the truth.” However, they fail to address a more fundamental question: Why is such a group of ordinary people deemed qualified to represent justice and deliver legally binding verdicts?

To answer this question, we must move beyond probability theory and return to the history and premises of the institution itself.

The Jury System: A Judicial Compromise Built on Religious Premises

The jury system did not naturally emerge from “democratic ideals” or “the advantages of collective rationality.” Instead, its emergence was largely a practical choice in medieval Europe under specific historical conditions. The key context at the time was not about making verdicts more scientific but about maintaining the continuity of judicial order as “trial by ordeal” gradually faded away.

During the era of trial by ordeal, humans did not bear ultimate responsibility for determining right or wrong in a case. The outcomes of trials by fire, water, or combat were interpreted as direct manifestations of God’s will. In 1215, when the European Church began prohibiting clergy from participating in trials by ordeal, this logical chain was severed. God no longer directly adjudicated cases through miracles, but the state lacked a comprehensive evidence system, investigative capabilities, and a professional judicial bureaucracy, creating a significant vacuum in judicial authority.

The jury emerged precisely within this vacuum. It was not about allowing ordinary people to “participate democratically in justice” but about enabling them to exercise judgment under a specific religious context, still believed to be supervised by God. Jurors were required to swear an oath before God, which was not a mere formality but a solemn commitment of the soul. Perjury was not just a procedural violation but a deception against God, carrying the risk of eternal damnation. It was under this premise that the judgment of ordinary people was deemed credible.

Thus, from its inception, the jury system was not a purely technical or procedural design but a logical framework built upon a religious worldview. Within this framework, the judge’s role was to apply the law, the jury’s role was to demonstrate “conscience” in making factual and moral judgments, and God was the ultimate arbiter. Ordinary people could adjudicate the fate of others not because they were more rational but because they were assumed to be in a state where their “conscience was supervised by God.”

This also reveals a radical assumption about human nature implicit in the jury system: that ordinary people possess the ability to distinguish between justice and evil. This assumption is not derived from experience or empirical evidence but stems from religious doctrine, which holds that “humans are created in the image of God and possess a universal conscience.” Once this premise is weakened, the jury system must seek new sources of legitimacy, which is precisely where problems begin to arise.

The Prosecutorial System: Replacing Religious Authorization with State Rationality

In stark contrast to the British jury system, the prosecutorial system gradually developed in continental Europe. The establishment of the procuratorate was not aimed at making justice more “democratic” but at making it more stable, controllable, and replicable.

The direct origin of the modern prosecutorial system can be traced back to the French King’s Prosecutor system, whose core function was not to represent victims or societal conscience but to uphold public legal order on behalf of the state. With the establishment of the Napoleonic codified legal system, prosecutors became a fixed role within the state’s judicial machinery, responsible for initiating public prosecutions, organizing evidence, and promoting the uniform application of the law.

In the 19th century, Germany highly theorized this system, shaping prosecutors into “objective legal officials.” Under this framework, trials were no longer understood as moral judgments but as highly specialized legal technical activities. Fact-finding, evidence evaluation, and legal application were all incorporated into a rational, self-consistent, and accountable system.

Under this institutional path, judicial authority no longer needed to rely on religious oaths or conscience supervision. Its legitimacy derived from state rationality, professional division of labor, and procedural stability. Although religion did not disappear in continental Europe, it was systematically excluded from the core of the legal system through successive reforms, remaining only as a cultural background or personal belief.

For this reason, the prosecutorial system does not rely on the reliability of ordinary people’s moral intuitions but on the system’s ability to function continuously. This makes it more stable in highly secularized and technocratic societies.

The Failure of Transplanting the Jury System Is Not Accidental

During the period of American ascendancy, under the influence of the U.S. system, many countries attempted to introduce the jury system, but almost all experienced “incompatibility.” This was not accidental but a result of structural issues inherent in the system itself.

In France, jurors were introduced but did not perform the genuine function of “conscience-based judgment”; they were essentially “citizen representatives sitting in.” Germany briefly experimented with the jury system in the 19th century but soon abolished it. German scholars at the time widely believed that randomly selected ordinary people lacked the legitimacy to adjudicate complex facts. This marked the first theoretical rejection of the jury system in the civil law tradition, with even Marx questioning the fairness of ordinary people serving on juries, arguing they were easily influenced by class interests. Japan and South Korea, following the U.S. model in the 20th century, introduced juries but found that verdicts were easily swayed by emotions and conflicted severely with professional judges. As a result, juries had very limited substantive power, serving more as symbolic participation. After the dissolution of the Soviet Union, Russia quickly copied the American jury system but soon discovered issues such as mafia infiltration and juror bribery, leading to significantly abnormal acquittal rates. Eventually, the system’s applicability had to be restricted. India also introduced the jury system at one point but abolished it within a year, primarily because juries were manipulated by public opinion, resulting in emotionally driven verdicts.

Examining these examples, it is evident that these countries experienced highly similar “incompatibility” issues when transplanting the jury system. Superficially, these appear as legal technical problems, but they fundamentally touch upon the system’s foundations.

First, the implicit religious premises of the jury system cannot be easily replicated. Whether it is the oath, conscience-based judgment, or the notion that “ordinary people represent justice,” in cultures where religion has receded or lacks a similar religious background, it is difficult to establish genuine psychological constraints and moral deterrence. The system can only rely on external procedural patches to barely function, often resulting in a form that exists in name but lacks substance.

Second, in countries that have already established a professional judicial bureaucracy and a prosecutorial-led structure, the jury is not an institutional necessity but an external variable. It inherently conflicts with existing evidence rules, responsibility allocation, and trial logic. Once verdicts become uncontrollable, state rationality inevitably opts to reclaim power.

Third, the modern environment of public opinion, media structures, and social polarization no longer supports the assumption that “random ordinary people can maintain independent judgment over extended periods.” Juries are more likely to amplify emotions, identity politics, or external influences rather than function as the idealized “collective rationality” depicted in probability models.

Precisely because the jury system itself heavily relies on religious premises and social trust, once these premises no longer exist in secularized societies, the system must rely on various “patches” to sustain itself. To mitigate the risks of jurors being influenced by emotions, public opinion, or external pressure, legal designers have had to add layers of procedures, such as juror screening, evidence presentation, discussion rules, judicial instructions, and review mechanisms. These patches are theoretically intended to preserve the system’s legitimacy and effectiveness, but they often result in exceptionally lengthy and complex judicial processes, high judicial costs, and limited improvements in the efficiency and reliability of jury verdicts. This explains why, in highly secularized and technocratic societies, the jury system struggles to form a sustainably operational framework. Its failure in transplantation is not “accidental” but an inevitable outcome of the mismatch between institutional logic and social foundations.