A few narrow doctrines let you argue that conduct meeting the elements of a crime should not be punished. The main legal defenses to criminal charges are self-defense, duress, necessity, entrapment, and mistake of fact. Each one is fact-specific, each one has firm limits, and in most cases you are the one who has to put evidence on the table.
Self-Defense
You can use force to protect yourself or another person from immediate unlawful force, even when that force would otherwise be a crime. The threat has to be immediate. A vague future threat or a verbal provocation, however ugly, does not justify a physical response. You must reasonably believe you are facing unlawful force right now and that responding with force is the only way to stop it.1Legal Information Institute. Self-Defense
Force has to be roughly proportional to the threat. A shove does not justify a knife. Deadly force is reserved for situations where you reasonably believe you face death or serious bodily injury. Once the threat ends, so does your justification; force used after an attacker has clearly backed off looks like retaliation to a court, not defense.1Legal Information Institute. Self-Defense
The defense also fails if you started the fight. A few jurisdictions let an initial aggressor regain the defense by genuinely and completely withdrawing from the confrontation, but juries do not take easily to that argument.
Stand Your Ground and the Castle Doctrine
Traditional self-defense law in many states includes a duty to retreat: you must try to safely escape before using force, especially deadly force. About half the states have eliminated that requirement through stand-your-ground laws, which let you use force without retreating as long as you are somewhere you have a legal right to be and the other requirements of self-defense are met.
Even where a duty to retreat applies in public, nearly every state recognizes the castle doctrine. Inside your own home, you have no obligation to flee from an intruder before using force, including deadly force.2Legal Information Institute. Castle Doctrine
Imperfect Self-Defense
Sometimes a person honestly believes their life is in danger and uses deadly force, but that belief is unreasonable by an objective standard. In states that recognize imperfect self-defense, this will not get you acquitted, but it can reduce a murder charge to voluntary manslaughter. The reasoning is that genuine fear, even mistaken fear, eliminates the malice required for murder. Not every state applies the rule, and the details vary where it does exist.
Duress
Duress applies when another person forces you to commit a crime by threatening you or someone close to you with immediate death or serious physical harm. The classic example is someone holding a gun to your head and ordering you to drive a getaway car. You committed a crime, but the alternative was being killed.3Legal Information Institute. Duress
For duress to hold up, the threat must come from another person, it must be immediate, and you must have had no reasonable way to escape. If you could have walked away, called the police, or found any other safe exit, the defense collapses.4United States Court of Appeals for the Armed Forces. CORE CRIMINAL LAW SUBJECTS: Defenses: Duress
Nearly every jurisdiction draws one hard line: duress is not a defense to murder. Courts have consistently held that no one may trade one innocent life for another.4United States Court of Appeals for the Armed Forces. CORE CRIMINAL LAW SUBJECTS: Defenses: Duress Duress is also unavailable if you voluntarily put yourself in a situation where coercion was foreseeable. Joining a criminal organization and then claiming duress when its leaders order you to commit a crime is the textbook rejection.
Necessity
Necessity resembles duress, but the pressure comes from circumstances rather than a person. You break the law because the alternative is a worse outcome. The Ninth Circuit’s model jury instructions lay out the elements: you faced a choice between two harms, you chose the lesser one, you acted to prevent something imminent, you reasonably believed your actions would prevent that harm, and you had no legal alternative available.5Ninth Circuit District & Bankruptcy Courts. Manual of Model Criminal Jury Instructions 5.8 – Necessity (Legal Excuse)
The textbook example is breaking into an empty cabin during a blizzard to avoid freezing to death. The property damage is real but trivial next to a human life. Speeding someone with a life-threatening injury to a hospital can qualify too, though a court will ask whether calling 911 was a viable alternative. The harm you cause has to be genuinely less serious than the harm you prevent.6Legal Information Institute. Necessity Defense
You cannot manufacture the emergency and then claim necessity to escape it. If you set a fire and then trespass on someone’s land to flee the flames, the defense will not save you. Courts examine whether you were reckless or negligent in bringing the situation about.
Entrapment
Entrapment is a defense against government overreach. It applies when law enforcement or a government agent induces you to commit a crime you would not have committed on your own.7Legal Information Institute. Entrapment A sting operation that offers you the chance to commit a crime you were already inclined to do is not entrapment. An undercover officer offering to buy drugs from a known dealer is lawful. An undercover officer spending months pressuring a law-abiding person into procuring drugs is not.
Most jurisdictions use the subjective test, which asks two questions. Did the government induce you to commit the crime? And were you predisposed to commit it anyway?7Legal Information Institute. Entrapment If the prosecution can show predisposition, the defense fails no matter how aggressive the tactics. A smaller number of jurisdictions use the objective test, which focuses entirely on whether law enforcement’s conduct was coercive or manipulative enough to push a reasonable, law-abiding person into the crime.
The Supreme Court drew the line in Jacobson v. United States (1992), where federal agents spent 26 months sending repeated mailings to a man before he ordered illegal material. The Court held that the government failed to prove he was predisposed before being targeted, and that agents “may not originate a criminal design, implant in an innocent person’s mind the disposition to commit a criminal act, and then induce commission of the crime.”8Justia. Jacobson v. United States, 503 U.S. 540 (1992)
Mistake of Fact
Most crimes require a specific mental state. If you take someone else’s coat from a restaurant hook genuinely believing it is yours, you lack the intent to steal. A reasonable factual mistake can negate the mental state the prosecution must prove, which means the elements of the crime are not all present.9Legal Information Institute. Mistake of Fact
The mistake generally has to be reasonable. A typical person in the same circumstances would have had to make the same error. For crimes that require a higher level of intent, even an unreasonable mistake can sometimes work, because the question is whether you actually held the required mental state, not whether your belief made sense to an outsider.9Legal Information Institute. Mistake of Fact
Mistake of fact is distinct from mistake of law. “I didn’t know that was illegal” almost never works; the legal system presumes you know the law. A narrow exception exists where you relied on an official statement of the law that turned out to be wrong, such as a misstatement in a statute, a judicial opinion, or guidance from an authorized government official.10Legal Information Institute. Mistake of Law It comes up rarely and succeeds more rarely still, but it is there for situations where the government itself misled you.
Who Has to Prove It
Most of these are affirmative defenses, which means you are not simply denying you did the act. You are admitting it and arguing you had a legally recognized reason. That shifts real work onto you and your attorney, and you will need evidence rather than a compelling story.11Legal Information Institute. Affirmative Defense
The standard varies. Some jurisdictions require you to prove your defense by a preponderance of the evidence, meaning more likely than not. Others only require you to raise enough evidence to put the defense in play, at which point the prosecution must disprove it beyond a reasonable doubt. The rules also differ by defense. Self-defense, for instance, is treated as an affirmative defense in some states but not others. Which framework applies in your jurisdiction matters, because it determines how strong your evidence has to be before a jury even considers the question.11Legal Information Institute. Affirmative Defense