Almost every crime is built from two components. The actus reus is the guilty act: a voluntary bodily movement, or a qualifying omission, together with any required result and attendant circumstances. The mens rea is the guilty mind: the mental state the defendant must have had about each of those elements. Prosecutors must prove both, and the two must coincide in time, so a defendant who forms the intent after the act is not guilty of the completed offense.
Elements
- A voluntary act. Reflexes, convulsions, movements during sleep, and conduct that is not a product of the actor's effort or determination are not voluntary.
- Omissions. A failure to act is criminal only where the law imposed a duty, arising from statute, contract, a special relationship, voluntary assumption of care, or the creation of the peril.
- Possession. Treated as an act where the defendant knowingly obtained the item or knew of it long enough to have got rid of it.
- Model Penal Code mental states. Purposely, meaning it was the conscious object; knowingly, meaning practical certainty as to a result or awareness of a circumstance; recklessly, meaning conscious disregard of a substantial and unjustifiable risk; and negligently, meaning a gross deviation from the care a reasonable person would use, whether or not the risk was noticed.
- Default rules. Where a statute states no mental state, recklessness is the Model Penal Code default, and a single stated mental state applies to every material element unless the statute clearly says otherwise.
- Strict liability. A small set of offenses, usually regulatory and lightly punished, require no mental state at all.
Leading cases
- Martin v. State: a man taken onto a highway by police could not be convicted of appearing drunk in public, because the appearance in public was not voluntary.
- Regina v. Cunningham: recklessness requires that the defendant actually foresaw the risk and went ahead anyway, not merely that a reasonable person would have foreseen it.
- Morissette v. United States: silence in a statute about intent does not eliminate it, and courts presume a mental state requirement for offenses derived from the common law.
Where students go wrong
The first mistake is stating one mental state for the whole crime. Under the Model Penal Code you analyze the mental state element by element, and the answer can differ for the conduct, the result and the circumstances.
The second is confusing recklessness with negligence. Recklessness requires actual awareness of the risk. Negligence does not, and that gap decides a great many homicide questions.
The third is treating any failure to act as an omission that can be punished. Find the duty first, because without one there is no actus reus at all.
FAQ
What does actus reus mean?
The guilty act. It requires a voluntary bodily movement or a qualifying omission, plus any result and circumstances the offense definition specifies.
What is the difference between purposely and knowingly?
Purposely means the result was the defendant's conscious object. Knowingly means the defendant was practically certain the result would follow, whether or not it was wanted.
Do the act and the intent have to happen at the same time?
Yes. The concurrence principle requires the mental state to actuate the act, so intent formed only after the conduct will not support the completed offense.
Related terms
Working through this in your own casebook takes longer than reading it here. Syllume starts from your syllabus and turns each assigned case into a brief you can study from.