In general, a defendant must act voluntarily in order to be guilty of a criminal offense.  The law also distinguishes between causing harm and failing to prevent harm.  Subject to a few exceptions, omissions are not criminally punishable.

The main criticism of the general rule against omissions liability is that it leads to morally repugnant results.  But a moral duty to act does not create a legal duty to act.

One of the concerns about imposing omissions liability is that it risks expanding the scope of criminal liability in ways that would strain an already overtaxed criminal justice system.  There are also line-drawing issues of what constitutes an omission. For example, if thirty people hear a woman’s cries for help as she is mugged, should all of them be equally liable, even if some hear her cries before others and therefore have more time to help? If legislatures define omissions liability broadly and leave enforcement to prosecutorial discretion, does this raise legality concerns?  And how, by the way, can legislatures define precise standards for what constitutes an omission?  Finally, punishing omissions might cause more harm than good, since people might feel compelled to provide aid they are not qualified to give.

Omissions liability also raises difficult questions of proof regarding a defendant’s mental state, or mens rea.  We will begin learning about these concepts in subsequent units.  For now, it is enough to observe that proof of mens rea is often established through circumstantial evidence based on a person’s actions.  But what does inaction prove?  It might reflect a state of shock or fear, or perhaps obliviousness to a situation, rather than criminal intent.

Exceptions to the General Rule

Failure to act can result in criminal liability when there is a duty to act. At common law, a duty to act arises under the three circumstances discussed below. Even when there is a duty to act, the offender must still possess the requisite mens rea to be criminally liable.

1) A person has a duty to act when he or she has a special relationship with the victim (a “status relationship”), such as a parent to a minor child, married couples to one another, and employer to employee.

2) A duty to act can also be created by an implied or express contract—for example, lifeguards and doctors may have a contractual duty to provide care.

3) A duty to act can also result by wrongfully creating a risk of harm. For example, a person who is driving recklessly and causes an accident has a duty to help anyone injured by his actions. Although there is less case law about accidental, non-culpable risk creation and justifiable risk creation, a few courts have suggested that a duty to aid arises in these situations as well. For example, if Fred shoots Mark in self-defense, Fred may still owe a duty to obtain medical care for Mark. A duty to act also results from voluntary assistance. One who begins to provide aid has a duty to continue to provide aid, unless the victim would be no worse off after the omission as before aid was provided.

Finally, a duty to aid can be imposed by statute. So-called “Good Samaritan Laws” require bystanders with knowledge of a victim’s need to provide reasonable assistance to the victim. The same arguments in favor of the general rule against omissions liability can be made against this type of statute.

Model Penal Code

The MPC does not differ from the common law. Omission liability is defined in MPC 2.01(3), which makes a person liable for an omission when the law explicitly makes an omission sufficient for the act, or when a duty to perform the omitted act is otherwise imposed by law.

Medical Omissions

Modern medical technology now allows some patients to be kept alive solely by artificial means.  If a doctor removes a patient’s respirator that helps the patient breathe, or if a doctor removes the tubes that provide a patient with food and water, has the doctor committed a voluntary act?  Or is the act of removing the machine merely an omission of providing future medical care?  Doctors owe a duty to their patients to provide ordinary, but not extraordinary, medical care. Are feeding tubes and respirators extraordinary care? In one case, the court reasoned that all care is extraordinary when the patient has no chance of recovery and the patient (or the patient’s next of kin) does not want continued medical treatment.

Social Harm

Recall that actus reus is defined as (1) a voluntary act or omission (2) that causes (3) social harm. Social harm, broadly defined, is an element of every offense. Society has an interest in protecting people and “things,” both tangible (such as cars or animals) and intangible (such as emotional security, reputation, or personal autonomy).

The social harm of an offense is usually set forth in the definition of the offense.  Social harm can include conduct elements, result elements, attendant circumstances, or a combination thereof.

A results crime is an offense in which the social harm is defined in terms of a prohibited consequence, regardless of how the consequence is brought about. For example, criminal homicide is a results crime: it requires the death of another human being.

A conduct crime is an offense in which the social harm is defined in terms of prohibited conduct, regardless of the consequences of such conduct.  Driving while intoxicated is a conduct crime, punishable even if the intoxicated driver is able to drive perfectly and does not cause any accidents.  Utilitarians justify punishing some conduct (like drunk driving) that might cause future harm absent specific or general deterrence.

A combination conduct and results crime criminalizes a consequence that occurs from specific conduct. For example, a first-degree murder statute that punishes death caused by an explosive device is both a conduct and result offense. The result of death must occur by specific conduct involving an explosive device.

Finally, many statutes contain attendant circumstances elements, which are certain facts or conditions that must be present for the social harm of the offense to occur. For example, common law arson is defined as “the malicious burning of the dwelling of another.” If someone burns down a grocery store that nobody lives in, he is not guilty of common law arson, because the attendant circumstance of a “dwelling” is not present. Similarly, if someone burns down her own house, the attendant circumstance of belonging to another is not present.


Q1. Suppose you are standing by a lever that controls which track a train takes. The train is heading toward a track that has five people tied to the tracks. There is no time to stop the train, and if you do nothing, five people will be run over and probably die. There is one person tied to the other track, and if you pull the lever, that person will be run over and probably die, but the five other people will be saved. All of the people are strangers to you. What do you do? Is there legally a difference? Is there morally a difference?

Q2. Do you think there is a difference between a doctor removing a respirator and a doctor removing a feeding and hydration tool? Do you think there is a difference between a doctor removing a tube, knowing that it will cause death, and actively injecting a patient with a substance that will cause death? Do you think the patient’s or family’s wishes should control? What if the family disagrees? What should the doctor and the courts do then?

Q3. Consider your answer to the last question when considering this case. A baby is born anencephalic, which means that she is born without most of her brain. Her brain stem can pump her heart and keep her alive, but she will never talk, walk, see, or respond to stimuli. Without a respirator, her heart and organs will fail and she will die in two weeks. Her parents want to donate her organs to help children on the transplant list. Doctors say if they wait until the baby’s heart fails on its own, her organs will be too deteriorated to donate. The parents and doctors want to harvest the baby’s organs now, before her heart fails, and before she needs a respirator to keep her alive. Should the courts allow this? Why or not? Is this an act or an omission? See In re T.A.C.P., 609 So. 2d 588 (Fla. 1992).