Actus Reus

Actus Reus (pronounced “Ack-tus REE-us”) is one of the two elements of criminal liability under common law, along with mens rea. Where mens rea is the mental state needed in order to be culpable of a crime, actus reus is the “guilty act” itself. To get a better understanding of these concepts, see the actus reus definition below.

Definition of Actus Reus

  1. An actual action that is a fundamental component of a crime, as compared with the perpetrator’s state of mind or intent.

Actus Reus Origin

The legal concept of actus reus as well as mens rea was first explored as a part of British common law. First recognized in the writings of English jurist Edward Coke, the phrase actus reus is drawn from the Latin phrase actus non facitreum nisi mens sit rea,which means: “an act does not make a person guilty unless (their) mind is also guilty.” The concepts of actus reus and mens rea can be boiled down to the idea that to be found guilty you must show culpability in both your thoughts and your actions.

Guilty Acts

Under both modern law as well as under the British common law, the prosecution is required to prove that a defendant made some form of action barred by law. But the concept isn’t quite so cut and dry. For an act to be the actus reus of a crime, it must be:

  • Voluntary; and
  • A concerted act, omission, or in some cases possession

When a defendant does something involuntary or that does not qualify as an act, there is no actus reus and therefore no crime.


What constitutes an act? The definition of an act has been debated by courts for years. In the 1962 case Robinson V. California, the United States Supreme Court struck down a law making it unlawful to be a drug addict. The court reasoned that being a drug addict was a status, not an act, and therefore could not be criminal.

With certain crimes, the circumstances under which the act occurs are critical in determining if a criminal act occurred. For example, the presence or absence of consent can be the difference between an act being the actus reus of a crime or not. It is not illegal to have sexual intercourse, but doing so without the consent of the other person would constitute the actus reus of rape.

Any crime that involves an act that is illegal in and of itself is known as a conduct crime. However, some acts are only criminal when the act leads to a specific illegal result. These are known as result crimes or consequence crimes.

Historically, an actus reus required the commission of a specific act. However, over the years the definition of an act has expanded into a broader idea of “conduct.” That is because American courts have upheld that both the failure to act as well as merely being in possession of a certain item or substance is enough to qualify as actus reus.


An omission is simply the failure to act. However, for an omission to qualify as actus reus of a crime, it must be shown that the victim of the crime would not have been injured but for the omission of the accused. Under the Model Penal Code, a criminal omission is defined as:

  1. the omission is expressly made sufficient by the law defining the offense; or
  2. a duty to perform the omitted act is otherwise imposed by law.

In other words, an omission may be considered actus reus of a crime is specifically criminalized via statute or if the omitted act was required by law.


Whether or not the mere possession of a substance or item constitutes an act has been a point of contention. Under the common law, mere possession in and of itself could not be the act associated with a crime. This conclusion became precedent under common law in the British case Regina v. Dugdale. However, many jurisdictions including the United States have rejected the conclusion in Regina v. Dugdale by considering the possession of an item as a voluntary act that may be used to establish criminality.


Not every act will constitute an actus reus of a crime. For conduct to qualify, it must be voluntary. The theory is best explained by a quote from Oliver Wendell Holmes: “a spasm is not an act. The contraction of muscles must be willed.”

Much like with an omission, the Model Penal Code has also expanded on what constitutes a voluntary vs. involuntary act. According to the MPC, involuntary acts include:

  1. a reflex or convulsion;
  2. a bodily movement during unconsciousness or sleep;
  3. conduct during hypnosis or resulting from hypnotic suggestion;
  4. a bodily movement that otherwise is not a product of the effort or the determination of the actor, either conscious or habitual.

Each of these examples is substantially different, but the end result in each of these cases is a lack of voluntariness required for an actus reus to be present.

Reflex or Convulsion

Generally speaking, it is not considered to be a voluntary act if a medical condition such as an epileptic seizure causes the movement of a body part that would otherwise be considered a criminal act. For example, an involuntary swing of an arm that strikes another person would not be considered battery.

There are exceptions to this broad principal, however. In some jurisdictions, a person with a history of seizures may be held criminally liable for injuries caused by the involuntary movement if prior to the seizure that person was engaging in dangerous or risky conduct. For example, in the New York case People v. Decina, a defendant was convicted of killing for children after suffering a seizure while driving. Because the defendant had a history of seizures and testified that he experienced one of the common warning signs of a seizure shortly before the collision, the act was not involuntary.


A similar issue of voluntariness is any act committed by a person that was asleep or otherwise lacking conscious control of their body. There have been instances of acts of violence or theft crimes committed by defendants while sleepwalking, in a fugue state, or otherwise unaware of their actions. Different jurisdictions treat these states differently. In some jurisdictions, unconsciousness or sleep is treated as a form of insanity defense, while in other jurisdictions it is its own distinct affirmative defense to a crime.

Hypnotic Suggestion

In certain jurisdictions, there is no actus reus when the actions would not have happened but for hypnosis or hypnotic suggestion. In some states, including New York and Montana, hypnosis can be used as evidence to show an act was not voluntarily. Under Canadian law, confessions made under hypnosis are not admissible in court as they are found to be involuntarily given.

Actus Reus Examples

The concepts discussed above are largely theoretical, which makes the use of examples helpful. Consider the examples below.

Examples of an Omission as an Act

Debra is a contractor that is required under state law to file her taxes annually. According to the statute, her tax filings are used to determine her tax liability, if any. When the date her taxes are due comes and goes, Debra still has no filed her returns. Because she is required by law to file the return, Debra’s omission could be construed as a criminal act.

Example of Conduct as an Act

Debra is walking down the street. She notices her arch nemesis, Vicky, approaching her on the sidewalk. Debra is still angry over something Vicky said to her years ago, and as Vicky comes near Debra swings her arm wildly and strikes Vicky in the face. Debra’s voluntary act of striking Vicky constitutes the necessary actus reus of assault.

Example of Involuntary Conduct Not Constituting Actus Reus

 Debra is walking down the street. She has been previously diagnosed with epilepsy, but her seizures are rare. She sees her arch nemesis Vicky approaching on the sidewalk. However, Debra is a mature adult and has no intention of assault Vicky. As Vicky passes her, Debra suffers a seizure. The seizure causes Debra’s arm to involuntarily swing wildly, striking Vicky in the face. Because the movement of her arm was involuntary and caused by a seizure, Debra has not committed a crime.