Why can relevant evidence still be excluded from a trial?

Even if evidence is relevant to a case, it may be excluded from a trial due to specific legal rules governing admissibility. While relevance depends on logical considerations, admissibility is determined by the law.1

Evidence is often excluded for the following reasons:

• Constitutional Violations: In the United States, the exclusionary rule prohibits the use of evidence seized by police in violation of the Fourth Amendment, which protects against unreasonable searches and seizures.23
• Privileges and Protections: Evidence may be inadmissible if it involves protected self-incrimination, confidential or professional communications, or government secrets.1
• Rules of Evidence: Common law jurisdictions maintain strict rules against hearsay and may exclude witnesses deemed incompetent to testify.1

These rules exist to uphold the rule of law and protect individual freedoms, even when such exclusions might prevent the conviction of a guilty person. While the exclusionary rule has faced controversy, it remains a fundamental mechanism for ensuring that state authorities adhere to constitutional standards.32