Mens Rea

Mens rea is Latin for "guilty mind". In criminal law, it is viewed as one of the necessary elements of a crime. The standard common law test of criminal liability is usually expressed in the Latin phrase, actus non facit reum nisi mens sit rea, which means "the act does not make a person guilty unless the mind is also guilty". Thus, in jurisdictions with due process, there must be an actus reus accompanied by some level of mens rea to constitute the crime with which the defendant is charged (see the technical requirement of concurrence). As a general rule, criminal liability does not attach to a person who acted with the absence of mental fault. The exception is strict liability crimes.

In civil law, it is usually not necessary to prove a subjective mental element to establish liability for breach of contract or tort, for example. However, if a tort is intentionally committed or a contract is intentionally breached, such intent may increase the scope of liability as well as the measure of damages payable to the plaintiff.

Therefore, mens rea refers to the mental element of the offence that accompanies the actus reus. In some jurisdictions, the terms mens rea and actus reus have been replaced by alternative terminology. In Australia, for example, the elements of the federal offences are now designated as "fault elements" or "mental elements" (mens rea) and "physical elements" or "external elements" (actus reus). This terminology was adopted to replace the obscurity of the Latin terms with simple and accurate phrasing.