Why did jury trials lead common-law courts to create more rules about admissible evidence?

In the context of Anglo-American law, the development of complex rules regarding the admissibility of evidence is deeply tied to the institution of the jury.

Because juries are composed of laypersons rather than legal professionals, common-law courts developed technical doctrines to control what information jurors are permitted to hear and consider during a trial. These rules serve several critical functions:

• Judicial Oversight: The judge acts as a gatekeeper, deciding what evidence is admissible to ensure that the jury’s verdict is based on reliable and relevant information rather than potentially prejudicial or misleading material.12
• Control of Outcomes: By regulating the flow of information, courts can exercise greater influence over trial outcomes. Historically, if a judge determined that evidence was improperly admitted, it could serve as grounds for an appellate court to reverse a verdict.3
• Fact-Finding Integrity: While juries are tasked with the "free evaluation" of facts based on their common sense, these evidentiary rules prevent the jury from being exposed to information that might improperly sway their judgment, thereby maintaining the integrity of the fact-finding process.2