The actus reus — sometimes called the external elements of a crime — is the Latin term for the "guilty act" which, when proved beyond a reasonable doubt in combination with the mens rea, i.e., the "guilty mind", produces criminal liability in common law-based criminal law jurisdictions Canada, New Zealand, England, Scotland and the United States. In the United States, some crimes also require proof of an attendant circumstance.
The mens rea is the Latin term for "guilty mind" used in the criminal law. 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 that "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). The exception is strict liability crimes (in the civil law, it is not usually necessary to prove a subjective mental element to establish liability, say for breach of contract or a tort, although if intentionally committed, this may increase the measure of damages payable to compensate the plaintiff).