Legal Definitions - onus probandi

Onus probandi is a Latin term that refers to the burden of proof. In legal contexts, it identifies which party has the responsibility to present sufficient evidence to convince the court, jury, or administrative body of a particular fact or claim. If that party fails to meet this burden, their claim or defense may not succeed.

• In a civil lawsuit for breach of contract: Imagine a small business owner sues a software developer, claiming the custom software delivered was faulty and did not meet the agreed-upon specifications. The business owner, as the plaintiff, carries the onus probandi. They must present evidence—such as the contract, expert analysis of the software, or communication logs detailing the issues—to prove that the software was indeed defective and that the developer failed to uphold their end of the agreement. If they cannot provide enough convincing evidence, their claim for damages will likely fail.

• In a criminal trial for assault: Consider a situation where an individual is accused of assault. In this type of case, the prosecution bears the onus probandi to prove, beyond a reasonable doubt, that the defendant committed the assault. The prosecution would present evidence like witness testimony, medical reports of the victim's injuries, or security camera footage. The defendant does not have to prove their innocence; rather, the prosecution must prove their guilt. If the prosecution fails to meet this high standard of proof, the defendant must be acquitted.

• In an administrative hearing for a professional license: Suppose a state nursing board initiates proceedings to revoke a nurse's license due to allegations of negligence in patient care. Typically, the nursing board, as the party bringing the action, would have the onus probandi. They would need to present evidence, such as patient records, witness statements, or expert testimony, to demonstrate that the nurse acted negligently and that their license should be revoked. The nurse would then have the opportunity to present their own evidence to refute these claims, but the initial burden of proving the negligence rests with the board.