Actus reus is the act—or the omission or failure to act when there is a duty to act—that comprises the physical elements of the commission of a crime. The actus reus generally must be voluntary bodily movements that constitute a crime.
In contrast, mens rea (meaning “guilty mind”) is the criminal intent element of a crime. It is the intent to commit a crime, or the knowledge that the action, or failure to act when there is a duty to act, will result in the commission of a crime.

In Oregon, as in other jurisdictions, the concept of actus reus requires that a defendant has engaged in a voluntary act, or an omission when there is a legal duty to act, that constitutes the physical elements of a crime. This means that for a person to be found guilty of a crime, it must be shown that they actually engaged in behavior that is prohibited by law, such as stealing property or physically harming another person. The requirement that the act be voluntary ensures that involuntary actions, such as those conducted while unconscious or during a seizure, do not typically constitute criminal acts. On the other hand, mens rea refers to the mental state of the defendant at the time of the crime. Oregon law recognizes various levels of mens rea, from intentional acts to those that are merely reckless or negligent. The presence of mens rea means that the defendant must have had a certain state of mind, such as intent or knowledge that their actions were wrong or would result in a prohibited harm, to be found guilty of many crimes. Both actus reus and mens rea are typically required to establish criminal liability, although there are exceptions for strict liability offenses where mens rea is not a necessary element.