Automatism is an excuse defense against criminal liability for defendants who committed a presumptively criminal act in a state of unconsciousness, semiconsciousness, or unawareness. Medically, the term automatism refers to motor behavior that is automatic, undirected, and not consciously controlled. The use of automatism as a legal defense is relatively rare and is typically claimed in cases where the defendant’s conscious awareness is compromised by epilepsy, brain injury, somnambulism (sleepwalking), or trauma. The automatism defense is recognized as a viable defense in U.S. and British courts, but the definitions and applications of the defense vary widely and are often inconsistent. The basis for the defense is that a defendant should not be held responsible for presumptively criminal actions because of the involuntary nature of the behaviors, leading to lack of criminal intent and voluntary criminal action.

Excuses and Justifications

In criminal law, there is a general rule that individuals are to be held legally responsible for their actions. Our fundamental and longstanding societal values and moral traditions allow for several exceptions in situations in which it would not be fair or just to hold persons criminally liable. These exceptions are discussed under the general heading of defenses, which, in turn, have been distinguished as justifications and excuses. Justifications seek to establish that even though the prosecution may have fulfilled its required burden to prove the basic facts of the offense, the act committed by the defendant was not criminal because, for example, it was done in defense of self, others, or property. Excuses essentially concede the wrongfulness of the act but seek to establish that the defendant is not criminally responsible because the act took place, for example, under conditions of duress or compulsion, immaturity, or insanity.

Automatism is an excuse defense that has been characterized as similar to the excuse of ignorance. That is, an automatism can be defined as an action taken without any knowledge of acting or without consciousness of what is being done. Automatism, however, is not simply a matter of acting out of ignorance. In the case of ignorance, a defendant may be acting based on an erroneous belief (e.g., the defendant believes that he or she is administering first aid but is, rather, exacerbating a medical condition of the victim), but in the case of automatism, the defendant is unaware that he or she is acting at all.

Actus Reus and Mens Rea

Except in cases of strict liability, any crime contains two elements: the actus reus (“guilty act”) and mens rea (“guilty mind”). The automatism defense seeks to prove that the defendant made physical actions (automatisms) that led to a bad outcome but did not perform a guilty act. As such, the automatism defense is the only excuse defense that is based on the actus reus element rather being purely a mens rea excuse defense (e.g., insanity). In an insanity defense, the defense acknowledges the guilty act but claims that the defendant should not be held blameworthy due to the lack of a guilty mind or intent.

Another way of understanding these two elements would be to consider if the presumptively criminal act was intentional or voluntary. Actions directed toward a goal are typically considered to be intentional. An automatism defense, however, claims that the actions taken are automatic and, therefore, not intentional. In the case of some automatic movements (e.g., loss of muscular control during a grand mal seizure), the absence of intentionality is obvious. In some cases, however, this judgment can be exceedingly difficult. For example, intentionality is far less obvious in a defendant who engaged in goal-directed aggression during a period of postictal confusion following a nocturnal partial complex seizure when the defendant appeared to be sleepwalking. The issue of volitional control (voluntariness) goes directly to the heart of the automatism defense. The Model Penal Code of the American Law Institute states that a defendant is not criminally liable if he or she does not commit a “vol-untary act,” which is defined to exclude “reflex or convulsion” or actions taken during “unconsciousness.” There can be no actus reus when the defendant does not commit a voluntary act. Typically, courts have required that volitional dyscontrol be total; that is, the actor (defendant) has no control over his or her actions.

The Automatism Defense: Case Law

Although its use is relatively rare, the automatism defense has been established as a criminal defense in courts in the United States and Britain. Courts vary widely, however, in definitions and applications of the defense. In the United States, for example, some courts have applied the rationale of an insanity defense, interpreting the involuntary behaviors associated with automatisms as a defect in reason that prevented the defendant from knowing the nature and quality of his or her act, therefore making an automatism defense a mens rea defense. Other courts have stressed the involuntary nature of the defendant’s actions, focusing on the lack of actus reus. British courts have made a distinction between sane and insane automatism. A defense of insane automatism requires that the defendant meet all three conditions of the British insanity defense (the M’Naghten standard), where the automatism would be the “disorder of reason” caused by a “disease of the mind,” leading to the defendant not knowing the “nature and quality of his act or that it was wrongful.” Defendants who raise an automatism defense and who meet M’Naghten standards would be adjudicated under the “not guilty by reason of insanity” (NGRI) standard. The defendant who raises the defense and who does not meet the standard would be claiming sane automatism, seeking to challenge that his or her behavior was simply not a voluntary act. If such a defense were successful, the defendant would be acquitted and not subjected to the possible consequences (e.g., commitment to a psychiatric facility) faced by an NGRI acquittee. British courts have indicated that sane automatism is an acceptable defense when the defendant has suffered from a defect of reason but not a disease of the mind, usually due to some external physical factor. The sequelae of a head injury or confusion as a result of the administration of drugs would be examples of such external causes of automatisms.

See also:

  • Assessment of Criminal Responsibility
  • Criminal Responsibility Defenses and Standards
  • Juries and Insanity Defense


  1. Borum, R., & Appelbaum, K. L. (1996). Epilepsy, aggression, and criminal responsibility. Psychiatric Services, 47(7), 762-763.
  2. Reznek, L. (1997). Evil or ill? Justifying the insanity defense. London: Routledge.
  3. Schopp, R. F. (1991). Automatism, insanity, and the psychology of criminal responsibility: A philosophical inquiry. Cambridge, UK: Cambridge University Press.