Criminal liability needs more than a bad thought. Actus reus is the physical element of a crime—the voluntary act, omission, or sometimes the result that the law prohibits.

It can be an affirmative action such as striking someone, or a failure to act when a legal duty exists, such as a parent’s duty to feed a child. The act must be voluntary; reflexes or movements during unconsciousness generally do not qualify. Some crimes also require a particular result, like death in a homicide statute.

Prosecutors must prove actus reus beyond a reasonable doubt along with the required mental state. Without a qualifying act or omission, no crime has occurred even if harmful intentions existed. Courts examine the statute carefully to identify exactly what physical conduct the legislature made criminal.

• Physical or conduct element of a crime
• Includes voluntary acts and certain omissions
• Must be proven along with mental state
• Does not include purely involuntary movements