Mens rea
Guilty mind required for criminal liability.
Mens rea is a legal concept in criminal law, derived from Law Latin for 'guilty mind,' referring to the mental state of a defendant accused of committing a crime. In common law jurisdictions, most crimes require proof of both mens rea and actus reus ('guilty act') for a conviction. The standard common law test is expressed in the Latin phrase 'actus reus non facit reum nisi mens sit rea,' meaning 'the act is not culpable unless the mind is guilty.' As a general rule, someone who acted without mental fault is not liable in criminal law, with exceptions known as strict liability crimes.
- field
- Criminal law
- known_for
- Mental state element of a crime
- legal_tradition
- Common law and Model Penal Code
- related_concept
- Actus reus
- exception
- Strict liability crimes
Lore & Background
Under common law tradition, judges often required a 'bad state of mind' in addition to an action or omission (actus reus) to find a criminal guilty. Over time, culpable mental states varied among different types of crimes, such as 'malice' for murder, 'fraudulence' for fraud, and 'willfulness and corruption' for perjury. The crime of manslaughter might require only a 'negligent' mind. The Supreme Court has explained that mens rea requirements for crimes are 'universal' and essential to 'mature systems of law,' undergirding notions of free will and morality.
Reader's Guide
The Model Penal Code (MPC), completed in 1962, set forth a highly influential formulation of mens rea that clarified discussion of different modes of culpability. The MPC recognizes four states of mind giving rise to criminal liability: negligently (a 'reasonable person' ought to be aware of a substantial and unjustifiable risk), recklessly (conscious disregard of such a risk), knowingly (practical certainty of the result or high probability of prohibited conduct), and purposefully (conscious desire for the result). These mental states work in a hierarchy, with negligence as the lowest and purposefully as the highest. The MPC also recognizes strict liability, where the actor's mental state is irrelevant, but only for mere violations. Over 34 states had adopted part or substantially all of the MPC by 1983, though the federal government has not adopted it. The distinction between common law and MPC approaches is illustrated by murder: federal law under 18 U.S.C. §1111 requires malice aforethought, while the Texas Penal Code (adopting the MPC) requires purposeful or knowing conduct causing death.
Did You Know?
- The standard common law test is expressed in the Latin phrase 'actus reus non facit reum nisi mens sit rea.'
- Exceptions to the general rule requiring mental fault are known as strict liability crimes.
- The Model Penal Code recognizes four states of mind: negligently, recklessly, knowingly, and purposefully.
- Over 34 states had adopted part or substantially all of the Model Penal Code as law by 1983.
More in Social Issues 1-24
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record