Duties Imposed by Law

The second route in § 2.01(3) leads to liability from a different direction than the first. Under subsection (b), an omission can support liability when a duty to perform the omitted act is "otherwise imposed by law."¹ The word otherwise points to a source outside the definition of the offense, and that is what separates this route from the statutory-omission route covered in the last section. The difference matters most for offenses defined by a result. Homicide describes causing a death and says nothing about failing to act, so the omission question arises most often under offenses of that kind.² A duty drawn from elsewhere in the law supplies the missing link. It gives the failure to act the same standing as a voluntary act, so a person who let another die can be treated as having caused the death when the law required that person to prevent it.³

Because the duty comes from outside the offense, it need not come from criminal law at all. It is enough that the duty arises under some branch of the civil law, which the criminal law then borrows.⁴ That is the general Anglo-American position: unless a penal statute itself requires a particular action, liability for an omission arises only when the law of torts or some other law imposes a duty to act.⁵ Borrowing has a practical logic. A duty that already exists in civil law has a defined content, it applies to identifiable people, and it was in force before the harm occurred, so the criminal law does not have to invent an obligation after the fact.

The central limit is that the duty must be a legal duty, and a moral duty will not do. In Jones v. United States, the court explained that the duty neglected must be a legal duty and not a mere moral obligation, that it must be imposed by law or by contract, and that the omission must be the immediate and direct cause of death.⁶ Pennsylvania's criminal code words its omission provision, 18 Pa.C.S. § 301(b)(2), the way § 2.01(3)(b) does. In Commonwealth v. Pestinikas the court read that language as separating a legal duty to act from a merely moral one, meaning an obligation whose performance depends only on humanity or a sense of justice or propriety.⁷

Two features of a legal duty explain why the Code insists on it. The first is fixed content: the law says who must act, what must be done, and how far the obligation reaches. Conscience cannot say how much effort or risk is owed, or by whom, so a moral standard has none of that. The second is timing. A legal duty exists before the harm and can be identified without looking at the outcome, which removes a problem of hindsight. Once someone has died, almost everyone nearby looks as though they should have helped, and a moral standard would let a prosecutor and jury pick the defendant after the fact. Tying liability to a duty the law had already imposed leaves that choice with the legislature or the civil law, where it was made in advance.

The retiree's position is the reverse of the one in Pestinikas, where an elderly man starved after the defendant agreed to feed him and knew he had no other way to obtain food, and the defendant was convicted of murder in the third degree.⁸ The agreement is the fact the retiree lacks, and it supplied a legal duty that sympathy alone could not. A felt obligation to help is a moral duty, and it supplies nothing under § 2.01(3)(b).⁹

Because the duty is what makes an omission count, it is something the jury must find. In Jones, the Government argued that the defendant had either contracted with the child's mother to care for the child or assumed his care and secluded him from his mother, and the evidence on both points conflicted. The instructions never told the jury it had to find a legal duty of care. The court reversed, calling a finding of legal duty the critical element of the crime charged and the failure to instruct on it plain error.¹⁰

Establishing a duty gets the omission into the act element and does nothing more. The omission must still cause the harm, and the defendant must act with the mental state the offense requires.¹¹ That is why most homicide-by-omission cases come out as involuntary manslaughter, where the defendant had no intent to kill. A case rises to murder only when the defendant refused aid intending death or with full knowledge of a great risk that death would follow.¹²

The same requirement governs a related setting. Liability generally does not flow merely from a failure to intervene, yet an omission in violation of a legal duty will suffice, so a person may become an accomplice by not preventing a crime the person has a duty to prevent.¹³ A train conductor who takes no step to stop the knowing transport of liquor on the train, a car owner who sits beside a driver speeding dangerously, and a parent who fails to stop a crime against the parent's own child are the standard illustrations.¹⁴

Courts have recognized several situations that supply a legal duty, and the subsections below take them one at a time.¹⁵ They share a structure that explains why the law chose them. In each, the person in danger depended on this particular defendant, or the defendant created or took over responsibility for the danger. That lets the law say which of the many people able to help was the one required to. Even where a duty exists, two limits on omission liability remain, namely the defendant's physical capacity to act and awareness of the facts calling for action, and a later section takes them up.¹⁶

Statutory and Civil Duties

The second route in § 2.01(3) asks whether a duty to perform the omitted act is "otherwise imposed by law," and the most common sources of that duty are legal rules found outside the definition of the charged offense.¹⁸ Two kinds of outside law qualify: a statute that commands someone to act, and the civil law (tort and family law, for example) that already requires the action. Either is enough, because the Code asks only whether some law imposes the duty, and courts accept that the duty may arise under any branch of the civil law.¹⁹ A parent's failure to provide a child with necessary food, shelter, and clothing is the standard illustration, since most states have laws requiring parents to supply them.²⁰ A homicide statute speaks only of causing death, yet the parent-support law supplies the missing obligation, so the failure to feed can stand in for an act. The next subsection treats the parent-child relationship itself as a source of duty. The point here is that a written legal command, whether in a statute or in civil law, is sufficient without more.

Students most often confuse this route with § 2.01(3)(a), and the confusion is understandable because the word statutory describes both. Under subsection (a), the law that defines the offense punishes the failure itself: failing to file an income tax return is the crime, so the same law that creates the obligation also makes breaking it an offense.²¹ Under subsection (b), the obligation sits in a separate source and the offense charged is defined by a result, so the prosecution borrows the duty to connect the omission to that result. The Hawaii aid statute in State v. Cabral shows the borrowing: it required a person at the scene of a crime who knows a victim is seriously hurt to obtain aid when that can be done without danger, and it was applied to perpetrators as well as bystanders, so a perpetrator who abused a child could be guilty of homicide for failing to aid.²² The aid statute created the duty, and homicide supplied the offense. A statute imposing a duty to care for another is also the first of the situations in which Jones v. United States recognized that failing to act breaches a legal duty.²³ Statutory duties can therefore appear on either route, and the dividing line is whether the charged offense itself punishes the failure to act.

Borrowing from civil law is workable because civil law has already done the work a criminal court would otherwise have to do. A court asked to punish a failure to act must know who had to act, what that person had to do, and how far the obligation extended, and a statutory or civil duty answers each question before any harm occurs. Tort law, for instance, defines a duty as a legal obligation requiring the actor to conform to a certain standard of conduct, and it recognizes an affirmative duty to act only where a source such as a statute, a contract, a relationship, or a status creates one.²⁴ That civil baseline matches the criminal one, so adopting it leaves intact the rule that a bystander's failure to help is not a crime. The borrowed duty only identifies which people fall within the exception. Organizations borrow duties in the same way. Under Model Penal Code § 2.07, a corporation may be liable for omitting a specific duty of affirmative performance that the law imposes on corporations.²⁵ The agent with primary responsibility for discharging that duty is accountable for a reckless omission to the same extent as if the duty rested on the agent personally.²⁶

The borrowed duty must still be a legal one. An obligation whose performance depends only on humanity or a sense of justice or propriety does not satisfy the Code, however strongly a community feels it, because nothing in the law identifies who is bound or what must be done.²⁷

Exam Analysis Steps

Because the two statutory routes look alike, it helps to sort a fact pattern before analyzing duty in detail. The sort runs as follows:

Read the charged offense and ask whether its own definition makes a failure to act sufficient, because if it does, the first route is satisfied and no outside duty is needed.
If the offense is defined by a result such as death, look for a source of obligation outside that definition, namely a statute or some branch of the civil law.
Confirm that the source is a legal duty owed by this defendant, since a felt moral obligation does not count.
Keep going past duty by checking causation, the required mental state, physical capacity, and knowledge of the facts calling for action, because a duty only gets the omission into the act element.²⁸

Special Relationships

A close relationship can itself supply the legal duty that § 2.01(3)(b) requires. Courts have long treated certain status relationships, among them husband and wife, parent and child, and master and servant, as a source of duty, so that one person in the relationship must act for the other when the other is in danger.³⁰ In Jones v. United States the court listed this ground, a status relationship, separately from the ground in which a statute imposes a duty to care for another. That separation shows that the relationship counts whether or not a statute speaks to it.³¹ The parent-child tie is the clearest example. Parents owe their children duties to feed, clothe, and generally protect them from harm, and a parent who fails to perform those duties can be held criminally liable when the child suffers neglect or harm as a result.³² A parent who withholds food or water from a child who then dies can therefore face a homicide charge, because the relationship supplies the duty and the omission takes the place of an act.

The reason the law picks out these relationships lies in dependence. A young child cannot secure food, shelter, or safety alone, so the child relies on the particular person who stands in the parental role. That reliance has a second consequence: because the child looks to that one person, help from anyone else is less likely to arrive, and the relationship puts on the parent a responsibility that strangers do not share. Dependence also explains why the duty reaches protection as well as provision. A parent who stands by while the other parent abuses the child is failing the protective half of the duty, which is why that failure can be treated as a breach of the duty owed to the child, as the earlier discussion of accomplice liability noted.³³

The mother-and-pool illustration shows the duty doing its work. When a child falls into a swimming pool, the mother ordinarily has a duty to rescue the child, or at least to attempt a rescue, because courts recognize the parent-child relationship as a source of duty, and if she stands and watches the child drown she can be charged with negligent homicide so long as she had the mental state that crime requires.³⁴ The duty gets her omission into the act element, and the remaining elements still have to be proved. The same illustration shows that the duty has limits: a mother who cannot swim is not liable for failing to jump in, though she may be liable for failing to throw a life preserver within her reach.³⁵ Those limits of capacity and knowledge are the subject of a later section.

The two adults differ in one fact, and that fact decides the result. Ability to swim, awareness of the danger, and inaction are the same for both, so the relationship is the only thing that turns a bystander's omission into a parent's.

Students lose this issue when they treat any close tie as enough. The relationships courts have recognized are specific ones, and a duty from relationship attaches only to a person who actually stands in one.³⁶ A scenario with many onlookers at a pool, including a lifeguard, a babysitter, the child's cousin, and a close friend of the parents, tests that point because each onlooker has to be analyzed separately.³⁷ The cousin and the friend are near the family but do not appear on the recognized list, so relationship alone gives them no duty. The lifeguard and the babysitter may well have duties, but those would come from contract or from taking charge of the child, which the following subsections address. Jones itself shows the same sorting. The child there had a mother who was his natural protector, and the Government relied on the contract and assumption-of-care grounds against the defendant, so the status ground never came into play.³⁸

Even a recognized relationship does not make one person the guarantor of the other's welfare. In Commonwealth v. Konz, a diabetic husband chose to forgo insulin treatment, and the court held that his wife was under no duty to seek medical aid for him when he died.³⁹ The dependence that justifies a parent's duty is missing when an adult makes that choice for himself. A parent's duty to obtain medical care for a child has also produced a separate dispute over religious belief. In Walker v. Superior Court, a parent who failed to secure medical treatment for a child out of sincere religious faith could be convicted of negligent homicide despite the Free Exercise Clause, whereas State v. Lockhart treated a good-faith belief in spiritual treatment as a possible defense to the misdemeanor of failing to provide care and so to manslaughter.⁴⁰ Both decisions treat the parent's duty as a given. They differ over whether a sincere belief excuses its breach, which is a question about the parent's mental state and defenses and not about whether a duty exists.

Contractual Duties

A person who agrees by contract to provide care for another takes on a legal duty to carry out that care, and a failure to perform can support criminal liability when it causes the other person's death.⁴² Jones v. United States lists this as the third of four situations in which a failure to act breaches a legal duty: the defendant has assumed a contractual duty to care for another.⁴³ Caregiving professions show how ordinary the source is. Doctors, nurses, and other caregivers in hospitals, therapy centers, and nursing homes take on duties to care for their patients through the contracts they make with those patients, so a nurse who ignores obvious signs of respiratory distress in a patient who then dies can be prosecuted for homicide.⁴⁴ The contract plays the same role here that a statute or a family tie plays in the neighboring categories. It is a source of obligation outside the homicide offense, and under § 2.01(3)(b) that is what allows an omission to stand in for an act.⁴⁵

Commonwealth v. Pestinikas shows the rule at work. Walter and Helen Pestinikas had agreed by oral contract to provide food and medical care for Joseph Kly, a 92-year-old man, and he died of starvation after they supplied neither, even though they knew he had no other way to obtain food.⁴⁶ The trial court told the jury that it could convict on the homicide charges only if it first found beyond a reasonable doubt that the defendants owed Kly a legal duty of care, and that the only source of such a duty in the case was an oral contract, so that without one the jury had to acquit.⁴⁷ The defendants argued that this instruction was error, and the Pennsylvania court rejected the argument. Pennsylvania's statute, 18 Pa.C.S. § 301, follows the Model Penal Code by allowing omission liability only where the offense definition makes the omission sufficient or a duty to act is otherwise imposed by law.⁴⁸ The court read that language as separating legal duties from moral ones, and it reasoned that a duty created by contract is legally enforceable and therefore a legal duty, so that failing to perform it may ground a charge of criminal homicide if the failure causes death and the other elements are present.⁴⁹ Because the evidence tied Kly's death to the defendants' failure to provide the food and medical care they had agreed to supply, the omission sufficed and the instruction was correct.⁵⁰

Two features of an agreement explain why the law treats it as a source of duty, and each answers a different worry. The first is reliance. A person promised care stops looking elsewhere, and relatives, neighbors, and agencies who learn that someone has taken responsibility tend to step back, so the agreement removes the other sources of help that would otherwise have existed. Because the Pestinikas defendants knew Kly had no other way to get food, their agreement was the only thing standing between him and starvation.⁵¹ The second feature is fairness to the defendant. An agreement fixes who must act, what must be done, and for whom, and the defendant chose to accept that obligation, so treating a breach as a legally consequential omission imposes no burden the person never took on. A bystander has made no agreement and has accepted nothing, which is why the same reasoning does not reach a bystander. Civil law reflects the same instinct: a person who undertakes services that will reduce the risk of physical harm to another, and who knows or should know it, owes a duty of reasonable care in carrying them out if a failure of care increases the risk or the recipient relies on the undertaking, and that duty can be breached by failing to act as well as by acting.⁵²

Jones shows the rule from the other direction, because there the contract theory never reached the jury in proper form. The Government argued that the defendant had either contracted with a child's mother to care for the child or had taken over the child's care and cut the child off from the mother, and the evidence on both points conflicted: Jones insisted that the mother lived with her and should have been caring for the child herself, while the mother testified that she lived with her own parents and paid Jones to care for both children.⁵³ Whether an agreement existed was therefore a fact question for the jury. The instructions never suggested that the jury had to find a legal duty, and the only reference to duty was the reading of the indictment's allegation that the defendants failed to perform their legal duty, so the appellate court called the finding of duty the critical element of the crime and reversed for plain error.⁵⁴ The reversal did not hold that a caregiver's passivity can never cause death. Had a properly instructed jury found that Jones undertook a duty of care, her entirely passive conduct would have been treated as causing the death.⁵⁵ The two decisions apply the same rule and differ in what the jury was asked to decide: in Pestinikas the instruction made the contract the dispositive question and the court approved it, while in Jones the instruction left the question out and the conviction failed.

Hypothetical Illustration

Two households live beside an elderly man who can no longer cook or shop for himself. The Okafors agree to bring him meals and fill his prescriptions in return for his monthly payment, and he stops asking anyone else for help. Weeks later the Okafors quit without telling anyone, and he dies of starvation. The Lindqvists next door pity him and say so often, but they never offer or agree to anything, and he would have died of the same cause on their watch. The Okafors' agreement is a legally enforceable source of duty outside the homicide offense, so their omission can stand in for an act if causation and the required mental state are proved. The Lindqvists' sympathy is a moral duty only, so the general rule that a bystander owes no duty controls and the omission cannot support the charge.

The two households differ in one fact, and that fact decides the result. Need, knowledge, and inaction are the same on both sides, and only the agreement turns a neighbor's inaction into a caregiver's omission. The contested issue in these cases is usually whether a real agreement to provide care existed. Good intentions, a habit of helping, or a community's expectation do not create a legal duty, because the duty must be one the person is bound to perform by law or by contract and not one that depends on humanity or a sense of propriety.⁵⁶

A contractual duty gets the omission into the act element and goes no further. The prosecution must still show that the failure to perform was the immediate and direct cause of death.⁵⁷ It must also prove the mental state the charged homicide requires, which is why most homicides by omission are involuntary manslaughter, while the same facts can be murder when the person refused aid intending death or knowing that death was very likely.⁵⁸ The Pestinikas conviction for third-degree murder reflects that second possibility. Whether the defendant could physically perform and knew the facts calling for action is the subject of a later section.

Creating the Risk

The duties covered so far, those from status and from agreement, exist before any emergency begins. A third source of duty looks at how the emergency began. Courts recognize that a duty to act arises when the defendant creates the risk of harm to the victim.⁶⁰ Section 2.01(3)(b) allows an omission to support liability when a duty to perform the omitted act is otherwise imposed by law, and risk creation is one of the ways the law imposes it.⁶¹ The duty it produces is to take reasonable steps to assist the endangered person, such as summoning help or giving aid within the defendant's reach.

The trigger is the defendant's own part in producing the danger, and two reasons support that choice. The functional reason is that the person who created a danger usually knows it exists and is standing closest to it, which puts that person in a unique position to avert the harm. The incentive reason is subtler. If the law imposed no duty, a person who endangered another could leave the scene and escape every consequence of the peril, and the victim would end up worse off than if that person had never acted at all. Allowing that result would reward the creation of risk, and the duty removes the reward. A bystander did nothing to bring about the victim's peril, so the general rule that no one must rescue a stranger continues to protect bystanders, while the duty reaches the one person whose conduct made the rescue necessary.

The duty does not depend on how the danger came about. A person who endangers another intentionally, one who does so negligently, and one whose conduct was entirely innocent all stand in the same position once the danger exists, because the recognized source of duty asks whether the defendant created the risk and adds no qualification about blame.⁶² The reason is that fault and duty answer different questions. Fault in creating the danger bears on the defendant's mental state and on which offense can be charged, while the duty bears only on whether a failure to help counts as an omission the law may treat as an act. A blameless creator is as well placed to help as a careless one, and the victim is as endangered, so a fault requirement would cut the duty off from the reasons that support it. Two limits keep the rule from sweeping too broadly: the omission must still cause the harm, and the defendant must have the mental state the charged offense requires.⁶³

Herman v. State shows the pattern in a decided case. The defendant provided the victim with an overdose of cocaine and then failed to summon medical assistance promptly, and the defendant was properly convicted of manslaughter.⁶⁴ Both halves of the pattern are present: conduct that put the victim in danger, followed by a failure to call for help that the defendant was in a position to make. State v. Cabral reaches a similar place by a different route. A Hawaii statute requires a person at the scene of a crime who knows that a victim is suffering serious physical harm to obtain aid if that can be done without danger, and the court held that it applies to perpetrators as well as to others, so a person who abused a child could be guilty of homicide for failing to aid.⁶⁵ The two sources overlap but differ in origin. The Cabral duty exists because the legislature wrote it and would bind a person at the scene who played no part in the harm, while the risk-creation duty exists because the defendant's own conduct produced the peril and needs no statute to support it.

Hypothetical Illustration

India tells Ima, honestly and with reasonable care, that the water off the dock is shallow enough to wade in, relying on a depth marker that turns out to be wrong. Ima wades out, loses footing at a drop-off, and begins to drown while India watches, knowing what is happening and able to throw a life ring that lies nearby. India was not negligent, but India's own statement is what put Ima in the water, so India owes a duty to render reasonable assistance, and the failure to throw the ring can stand in for an act if causation and the required mental state are proved. Now remove the statement. Ima wades in with no word from India and begins to drown, and India, who dislikes Ima, does nothing. Nothing India did created the danger, India has no family tie, contract, or caretaking role, and dislike is not a source of legal duty, so the general no-duty rule controls and the omission cannot support a charge.

The two versions differ in one fact, and that fact decides the result. India's awareness of the danger, ability to help, and inaction are the same in both, and India's feelings toward Ima play no part in either. Only the question whether India's conduct brought the danger about changes, and the answer to that question determines whether a duty exists.

Students lose this issue when they require fault in creating the danger before finding a duty, because that reading lets an innocent creator walk away from a victim who is drowning because of the creator's own conduct. The error runs in the other direction as well. Proximity, ill will, and the ability to help are not enough by themselves, and a person who had no part in causing the peril owes no duty on this ground. Even where the duty exists, it is a duty to take reasonable steps and not a guarantee that the victim will be saved. It gets the omission into the act element, and the remaining elements of the offense must still be proved, including causation and the required mental state. The limits of physical capacity and knowledge of the facts are the subject of a later section.

Assuming Care of Another

A fifth source of duty comes into play when a person who owed nothing at the start takes charge of someone who needs help. The earlier sources do not fit this situation. A contract requires an agreement, and risk creation requires that the defendant have brought about the danger, yet a person who finds a helpless stranger has promised nothing and caused no peril. The law still recognizes that such a person can acquire a duty through what he does next. In Jones v. United States, the court listed as one ground of criminal liability the case where one has voluntarily assumed the care of another and so secluded the helpless person as to prevent others from rendering aid.⁶⁷ Broader statements of the same category describe a defendant who otherwise would have no duty and who voluntarily assumes care of a person in need of help.⁶⁸ The Model Penal Code formulation, which Pennsylvania's § 301(b)(2) tracks, asks only whether a duty to perform the omitted act is otherwise imposed by law, and a duty that arises under some branch of the civil law is enough.⁶⁹ A person who assumes care therefore supplies the duty that lets the omission stand in for an act.

The Jones formulation has two parts, and each does separate work. The first is voluntary assumption: the defendant must have chosen to take over the care of the person, which is what distinguishes the defendant from a bystander who merely witnesses the need. The second is the effect of the takeover: the helpless person must have been so secluded that others were prevented from helping. Jones shows how this ground is litigated. The Government's alternative theory was that the defendant had assumed the care of a child and secluded him from his mother, his natural protector, and the evidence on that point conflicted, so whether she had done so was a question for the jury.⁷⁰ Because the instructions never asked the jury to find a legal duty, which the court called the critical element of the crime, the conviction was reversed.⁷¹

The seclusion element also explains why the duty exists at all. A helpless person who has been taken in stops being one of many people whom others might assist and becomes dependent on the one who took charge. Neighbors, relatives, and passersby who see that someone has stepped in tend to step back, and if the taker has closed the door, they cannot help even if they wish to. The victim ends up worse off than if the taker had never intervened, since the help that would have been available is gone and nothing has replaced it. If the law imposed no duty, a person could take control of a helpless stranger and then neglect that stranger, and the takeover would earn the same freedom from liability that a bystander enjoys. The duty removes that result by holding the person responsible for the task the takeover displaced. The same structure keeps the duty narrow, because it attaches only to the person who took charge, and bystanders who leave others free to help remain under the general no-duty rule.

Tort law recognizes a close parallel. Under Restatement (Third) of Torts § 44, an actor who, despite no duty to do so, takes charge of another who reasonably appears imperiled and helpless or unable to self-protect has a duty to exercise reasonable care while the other is within the actor's charge.⁷² The comments set its boundaries: the duty is limited in scope and duration to the peril the other faces, and it requires that the actor voluntarily undertake a rescue and actually take charge of the other.⁷³ The rule applies however the person became helpless, whether through intoxication, the conduct of others, or a force of nature, so long as the rescuer took charge intending to help with the peril then existing.⁷⁴ Whether a person is imperiled and helpless depends on context: someone who is drunk in a chair at home may be neither, while the same person behind the wheel of a car would be both.⁷⁵ Section 44 does not mention seclusion, while the Jones formulation does, so an answer on an exam should state the takeover and the displaced help together, which satisfies both statements of the rule.

Decided homicide cases show the pattern in family settings. A Florida decision, Corneil v. State, treated as manslaughter the conduct of a woman entrusted with her grandchild who became so intoxicated that the child was suffocated while its screams could be heard throughout the neighborhood.⁷⁶ Placing a helpless child in someone's charge makes that person answerable for what happens when the person stops caring for the child. The materials that follow Jones put the question in the reverse direction, with a daughter convicted of involuntary manslaughter of her mother after the trial court found the death resulted from her criminal negligence in failing to provide heat, food, liquids, and other necessaries in Davis v. Commonwealth.⁷⁷ A relative who takes over a dependent person's daily care can fit two sources at once, family status and assumed care, so an answer should test each.

Hypothetical Illustration

Marcus finds a stranger slumped on a bench in a train station, feverish and unable to stand. He half-carries the stranger to his apartment nearby and, when a neighbor offers to call an ambulance, answers that he has everything under control and closes the door. For two days he gives the stranger neither water nor medical attention, and the stranger dies of dehydration. Marcus owed nothing when he first saw the stranger, but he voluntarily took charge of a helpless person and cut off the help the neighbor offered, so he assumed a duty to provide care, and his omission can stand in for an act if causation and the required mental state are proved. Now change one fact. Another commuter sees the same stranger on the same bench and walks on without stopping. The commuter took charge of no one, other travelers remained free to help, and no help was displaced, so no duty was assumed and the general rule that a bystander owes no duty controls.

The two scenes differ in a single fact, and that fact decides the result. The stranger's illness, the visibility of the need, and the inaction that followed are identical, but only Marcus took charge and shut out other help. The trap on this issue lies in treating actually taking charge as satisfied by a glance, a kind word, or an offer that was never carried out, because the Restatement rule requires that the actor undertake a rescue and take charge of the other, and the Jones formulation requires that others be kept from helping.⁷⁸ Even when the duty is established, it only gets the omission into the act element. The prosecution must still prove that the failure to act caused the death and that the defendant had the mental state the charged offense requires, which is why most such homicides are involuntary manslaughter.⁷⁹ Physical capacity and knowledge of the facts, the remaining limits on omission liability, are the subject of a later section.