Necessity Defense vs. Duress Defense
A detailed comparison of these two criminal law rules, including key differences, exam strategies, and guidance on when to apply each.
Overview
Necessity and duress are both justification/excuse defenses that permit a defendant to argue that criminal conduct was compelled by circumstances. However, they differ in the source of the compulsion, the nature of the threat, and their theoretical foundations.
The necessity defense (also called the "choice of evils" defense) applies when a defendant commits a crime to avoid a greater harm caused by natural forces or circumstances beyond anyone's control. The defendant must show that they faced a choice between two evils and chose the lesser one, that there was no legal alternative, that the harm avoided was greater than the harm caused, and that the defendant did not create the emergency. The classic example is breaking into a cabin during a blizzard to avoid freezing to death. Necessity is a justification defense, meaning the defendant's conduct was the right thing to do under the circumstances.
Duress, by contrast, applies when a defendant commits a crime because another person threatened them with imminent death or serious bodily harm. The threat must come from a human source, not natural forces. The defendant must show that the threat was of imminent death or serious bodily harm, that the threat would cause a reasonable person to commit the crime, and that the defendant was not at fault in exposing themselves to the threat. Duress is traditionally an excuse defense, meaning the defendant's conduct was wrong but they are not morally culpable because they were coerced. Importantly, duress is not a defense to murder at common law (though the MPC does not create this exception).
Key Differences
| Aspect | Necessity Defense | Duress Defense |
|---|---|---|
| Source of compulsion | Natural forces or circumstances (non-human threat) | Human threat of imminent death or serious bodily harm |
| Theoretical basis | Justification: defendant chose the lesser evil | Excuse: defendant was coerced and lacked free will |
| Defense to murder? | Theoretically available if killing one saves many (controversial) | Not a defense to intentional murder at common law |
| Balancing test | Harm avoided must be greater than harm caused | No balancing; focuses on whether a reasonable person would have yielded to the threat |
| Who created the situation | Defendant must not have created the emergency | Defendant must not have recklessly placed themselves in the threatening situation |
Exam Tips
On a criminal law exam, distinguish necessity from duress by identifying the source of the threat. If the threat comes from nature or circumstances (a storm, a fire, a medical emergency), analyze necessity. If the threat comes from another person (a coercion scenario), analyze duress. Remember that duress is not a defense to murder at common law, while necessity theoretically could be (though this is extremely rare and controversial). Under the MPC, both defenses are treated more leniently: the necessity defense is codified as "choice of evils" (Section 3.02), and duress is broader because it does not exclude murder and uses a "person of reasonable firmness" standard.
When to Apply Which
Apply necessity when natural circumstances force the defendant to choose between two harmful courses of action. Apply duress when another human being coerces the defendant into committing a crime through threats of imminent bodily harm or death. If the exam involves a human threat, use duress. If it involves a natural emergency or situational compulsion, use necessity. Always check whether the defendant contributed to the situation, as both defenses are unavailable if the defendant created the threatening circumstances.