What is self-defense?
Self-defense is a legal justification that makes force lawful when it's used to protect yourself from an imminent, unlawful attack. Because it's a justification rather than an excuse, a person who acted in valid self-defense hasn't committed a crime at all. Most U.S. self-defense law comes from state statutes and court decisions, so details vary widely across the country.
Courts generally ask four questions: Was the threat imminent? Did the defendant honestly and reasonably believe force was needed? Was the force proportionate to the threat? Was the defendant the initial aggressor? Once a defendant offers some evidence of self-defense, most states require the prosecution to disprove it beyond a reasonable doubt.
- Imminence
- The threat must be happening now or about to
- Reasonableness
- Honest belief a reasonable person would share
- Proportionality
- Deadly force only against death or serious injury
- Korean term
- 정당방위 (Criminal Act art. 21)
Two people can face the same attack and get opposite verdicts. Where it happened, and whether they could have walked away, often decides the case.
Reasonable force and deadly force
Non-deadly force may be used against an unlawful threat of any bodily harm. Deadly force, meaning force likely to cause death or serious bodily injury, is justified only when the person reasonably believes they face death, serious injury, or in many states certain violent felonies such as kidnapping or rape. Using a gun against a mere shove, for example, usually fails the proportionality requirement.
The belief must be both honest and reasonable. In People v. Goetz (1986), New York's highest court held that reasonableness is judged by an objective standard, considering the defendant's situation, rather than by what the defendant personally believed. If a belief is honest but unreasonable, some states allow imperfect self-defense, which reduces murder to manslaughter rather than leading to acquittal. An initial aggressor generally loses the right to claim self-defense unless they clearly withdraw from the fight and communicate that withdrawal, or the other side escalates from non-deadly to deadly force.
Duty to retreat, castle doctrine and stand your ground
The biggest split among states is the duty to retreat. In a minority of states, a person must retreat before using deadly force if they know they can do so in complete safety. Almost every state, however, recognizes the castle doctrine, which removes any duty to retreat inside one's own home, and some extend it to vehicles and workplaces.
Starting with Florida in 2005, a majority of states have adopted stand-your-ground laws, by statute or court decision, removing the duty to retreat anywhere a person has a lawful right to be. Some also grant immunity from prosecution or civil suits and hold pretrial hearings on the claim. The laws drew national attention after the 2012 killing of Trayvon Martin in Florida, and studies have linked them to increases in firearm homicides, a finding supporters dispute.
- Brown v. United States (1921)
- "Detached reflection cannot be demanded in the presence of an uplifted knife"
- People v. Goetz (1986)
- Reasonableness is an objective standard
- District of Columbia v. Heller (2008)
- Self-defense is central to the Second Amendment right
Defense of others and property
Most states let a person defend a third party to the same extent the third party could defend themselves. Force to protect property is more limited: reasonable non-deadly force may be used to stop theft or trespass, but deadly force solely to protect property is generally not allowed. The classic case Katko v. Briney (1971) held homeowners liable for a spring-gun trap that injured an intruder in an unoccupied farmhouse. The right to keep firearms for self-defense is covered in the Second Amendment.
How Korea compares
Korea's Criminal Act (art. 21) excuses defensive acts against a present, unjust attack if there is a "reasonable cause," judged by the severity of the attack, the means used and the balance of interests. Courts read this narrowly and rarely accept it in mutual fights. In the 2016 "burglar brain death" case (2016도2794), the Supreme Court upheld the conviction of a homeowner who kept beating a burglar who'd already been subdued and was trying to flee, ruling it was neither self-defense nor excessive defense. Korea has no castle doctrine or stand-your-ground rule.
Excessive defense may reduce or waive punishment (art. 21(2)), and is not punished when it results from fear or panic at night or in similar circumstances (art. 21(3)). A Korean report on Self-Defense Law in Korea vs. the U.S.: Requirements, Excessive Defense, Key Korean Cases and Stand Your Ground compares these rules with U.S. law. The broader principle that crimes and defenses must be defined by statute is explained in nullum crimen sine lege.
| United States | Korea | |
|---|---|---|
| Source | State statutes and case law | Criminal Act art. 21 |
| Duty to retreat | Varies; none at home | No formal duty, but alternatives weigh on "reasonable cause" |
| Home defense | Castle doctrine | No special rule |
| Excessive force | Conviction, sometimes imperfect self-defense | Reduced or waived penalty |
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Criticism and debate
Supporters of broad self-defense laws say people shouldn't have to flee from criminals or second-guess themselves in a split-second crisis. Critics argue stand-your-ground laws encourage escalation, are applied unevenly by race and make it harder to prosecute avoidable killings. In Korea the debate runs the other way: many people think courts are too strict and punish victims who fight back. How these claims play out in court is covered in U.S. criminal procedure.
The law doesn't expect perfect judgment in a crisis. It expects a response a reasonable person would see as necessary, and it stops protecting you once the danger is gone.
- What are the requirements for self-defense?
- An imminent unlawful threat, an honest and reasonable belief that force is needed, force proportionate to the threat, and generally not being the initial aggressor.
- What is the difference between stand your ground and the castle doctrine?
- The castle doctrine removes the duty to retreat in your home; stand-your-ground laws remove it anywhere you have a lawful right to be.
- Can you use deadly force to protect property?
- Generally no; deadly force is limited to threats of death or serious injury, though some states allow it against certain violent felonies or home intruders.
References and official sources
- Self-defense, Wex. Cornell LII
- Stand your ground, Wex. Cornell LII
- Castle doctrine, Wex. Cornell LII
- District of Columbia v. Heller, 554 U.S. 570 (2008). Cornell LII
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