A crime that is the product of conscious choice and independent will.
No crime can be committed by bad thoughts alone. One basic premise of U.S. law is that every crime requires the commission of some act before a person may be held accountable to the justice system. A criminal act may take the form of affirmative conduct, such as the crime of murder, or it may take the form of an omission to act, such as the crime of withholding information from the police. However, in order for an act to be considered criminal, it must be voluntary.
To constitute a voluntary act for which a person may be held criminally liable, the act must result from the person's conscious choice. The choice need not be the product of thorough deliberation but may stem from an impulse, as long as the person is physically and mentally capable of exercising restraint and discretion consistent with the requirements of the law. A person who suddenly slips on a mountain trail and reaches out to grab the arm of a bystander to avoid falling has acted voluntarily because his mind has quickly grasped the situation and dictated a response.
Acts over which a person has no physical or mental control are not voluntary. A muscle reflex driven by the autonomic nervous system, such as a knee jerk, is not considered voluntary under the law. Acts committed during seizures, convulsions, hypnosis, or unconscious mental states also lack sufficient volition and judgment needed to impose criminal liability. For the same reasons, acts committed during episodes of sleepwalking are not considered voluntary.
On the other hand, acts that are not fully the result of independent will but are committed with extreme indifference to human life are usually treated as voluntary. A conscious person who points a loaded gun at another, for example, will typically be held liable for any harm that results from its accidental discharge because the act of brandishing a loaded gun is treated as a voluntary choice manifesting a recklessness toward the safety of others. Similarly, an intoxicated person who passes out behind the wheel of a car cannot escape liability for any criminal acts that ensue, because they followed from the voluntary acts of drinking and driving. Persons who have a history of seizures, fainting spells, or blackouts may be held responsible for criminal acts that result during such episodes if a court finds that reasonable precautions could have been taken to avoid the dangers created by these physical and mental conditions.
In the majority of criminal cases, the voluntary nature of a defendant's act is not at issue. Until something in evidence indicates to the contrary, a court may presume that a defendant has acted with the intent to carry out the bodily movements for which she is being prosecuted. The law expects every person to take responsibility for her own actions and anticipate the natural consequences that might reasonably follow from particular behavior. Medical testimony is commonly required to place a defendant's mental state into question and raise the defense of voluntariness before a judge or jury.
Involuntary criminal acts should be distinguished from acts that are the product of duress. Duress includes the use of force, or threat of force, to coerce another to commit a criminal act. Crimes committed under duress are considered voluntary because an individual's decision to succumb is normally based on a cost-benefit analysis in which he weighs the consequences of acting and refusing to act. Nonetheless, the law protects individuals who succumb to coercion by allowing them to assert the defense of duress. The defense of duress is based on the idea that the deterrent and retributive value of criminal law is not served by punishing individuals for behavior that is not the product of free and independent will.