Mens Rea & Actus Reus: Concurrence & Examples

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  • 0:04 The Crime
  • 1:05 Actus Reus
  • 1:44 Omission
  • 2:30 Mens Rea
  • 3:28 Concurrence & Causation
  • 4:47 Lesson Summary
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Lesson Transcript
Instructor: Kenneth Poortvliet

Kenneth has a JD, practiced law for over 10 years, and has taught criminal justice courses as a full-time instructor.

The written law expresses the elements of a crime. External to those are general elements that must also be proven. In this lesson, we'll define mens rea and actus reus and show the role they play in the prosecution of a crime.

The Crime

Gilda injected poison into her roommate Chevy's iced tea, knowing Chevy would drink some after work like he always did. She got in her car and backed out of the driveway, wanting to be gone when he came home. Suddenly she felt a thump and heard a scream. She just backed over Chevy coming home early. If he dies, is she guilty of murder?

In general, crimes are broken down into elements that the prosecutor must prove to convict someone of a crime. Statutory elements are those needed elements expressed in the written law. In addition, there are general elements of every crime that are external to the written law but are just as necessary to prove. They are:

  • Actus reus (Latin for ''guilty act''): the voluntary act that is at the core of a crime

  • Mens rea (Latin for ''guilty mind''): the evil state of mind of the person committing the guilty act

  • Concurrence: the guilty act and the guilty mind need to be in concert for a crime to have been committed

  • Causation: the act must have been the cause of the harm expressed in the crime

Actus Reus

A long-held legal axiom is that for a crime to occur, there has to be an act. Otherwise, we'd all be guilty of some evil thought at some time. Status crimes are crimes for existing in a certain condition, like being a drug addict). Status crimes are not criminal in nature, and because of that, to act would be unconstitutional. So what is an act? Conventionally it is ''something done,'' whether voluntary or involuntary. To be a crime, an act is something done by a person voluntarily. Actus reus then is something done by a person, voluntarily, that's prohibited or unlawful. For example, shooting another person in the head is an unlawful act.


So, can a lack of action be an action? The law also allows inaction as an act if you were supposed to be doing something. This is an omission, and if a person is under a duty and does nothing, then that can be an ''act'' for a crime. For example, a police officer sees someone being beaten and does nothing. By law, a police officer is under a duty to help. A contract for employment such as a private lifeguard or security personnel can also create a duty to act.

Conversely, this means that a person not under a duty has no obligation to act, even if someone would be harmed by the inaction. For example, Bobbing Bob bobs down the river in obvious danger while Timid Timmy just watches Bob bob. There is no crime as Timid Timmy is not under a duty to help.

Mens Rea

In most systems of justice, a person is not convicted of a crime unless they intended to break the law. The exceptions being strict liability laws such as littering and traffic laws for which intent is irrelevant. For more serious crimes, some intent to do something unlawful is required, referred to as mens rea. This is to avoid putting someone in jail for an unintended act. For example, Swinger Sam is swinging his bat while practicing his swing. Dim Donny sneaks up behind as a joke and get smacked in the head and dies. We wouldn't put Swinger Sam in prison for murder because he had no intent to hurt Dim Donny.

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