Affirmative Defenses in Criminal Cases

Sometimes a criminal defendant is entitled to acquittal even though the prosecution has proven every element of the charged offense. This happens when the defendant successfully raises and the jury accepts an "affirmative defense" that operates by law to exonerate the defendant.

Read on to learn about affirmative defenses and how they differ from failure-of-proof defenses.

Defense Strategies in a Criminal Case

In a criminal prosecution, the prosecutor must prove every element of the charged offense beyond a reasonable doubt (a near-certainty standard). Elements of an offense are the components of conduct, intent or mental state, and harm that together make something a crime. Defendants often try to beat the charges by poking holes in the prosecution's case (a failure-of-proof defense) or by raising an affirmative defense.

With a failure-of-proof defense, the defendant tries to convince the factfinder (judge or jury) that the prosecution can't meet its burden as to each element. Here, the defense tries to raise reasonable doubt in the minds of the jurors. An affirmative defense, on the other hand, doesn't try to negate an element of the crime or prove a defendant's innocence.

What Is an Affirmative Defense?

Affirmative defenses prevent a conviction even when the prosecutor has met its burden of proving the crime. Defendants use affirmative defenses to justify, excuse, or mitigate the wrongful conduct that's been proven or admitted. Defendants raise affirmative defenses and often bear the burden of proving the defense.

Self-defense is one example of an affirmative defense. The prosecution may have proven that the defendant attacked the victim. Nonetheless, the defendant will be acquitted if their use of self-defense is found reasonable.

What Are the Different Types of Affirmative Defenses?

Affirmative defenses generally fall under one of three categories—justifications, excuses, and nonexculpatory defenses.

Justification defenses recognize the unlawful conduct but deem it justified under the circumstances. It essentially negates the wrongfulness of the act. Self-defense is an example.

Excuse defenses go to the actor's blameworthiness. These defenses negate their culpability. For instance, the duress defense excuses an actor's conduct based on another coercing them to act.

Nonexclupatory defenses don't consider the actor or their conduct. These defenses represent policy decisions that bar a defendant's convictions, such as statutes of limitations or diplomatic immunity.

What Are Examples of Affirmative Defenses?

States differ in what they consider affirmative defenses, but some common examples are discussed below.

Self-Defense

Self-defense typically applies in murder, assault, and battery cases. A person may use reasonable force against another to protect oneself against imminent harm. Belief in the perceived harm must be reasonable and the force used to stop it must be proportional. So, if an attacker is trying to hit you, hitting back would be justified. Pulling out a gun and shooting likely wouldn't be (unless you reasonably feared the attacker could kill you or grievously harm you).

Defense of Others

If a victim of threatened harm would be justified in using self-defense, a third person can step in and use defensive force on their behalf. So, if a third party sees someone being hit and thrown to the ground by an attacker, the third party would be justified in grabbing and punching the attacker to stop the attack.

Defense of Habitation

An occupant of a home may use reasonable force against an intruder. Deadly force may be justified when there's a reasonable belief that the intruder intends to commit a violent felony. (In some states, an owner's belief of violent harm is presumed during a home invasion.) For example, if a homeowner awakens at 2 a.m. to see someone trying to open their bedroom window, the homeowner may be justified in grabbing a knife and trying to stab or cut the intruder.

Defense of Property

A property owner can use reasonable force to prevent theft or destruction of their property. However, deadly force is not permitted unless the person's life or violent force is threatened. For example, if a person sees their bike being stolen, they can't use deadly or violent force against the thief, but they would likely be justified in throwing a helmet or other object at the thief to prevent the theft.

Necessity Defense

Sometimes referred to as a choice between two evils, the necessity defense justifies unlawful conduct when it's necessary to avoid a greater, imminent harm. Generally, the "necessity" or emergency must occur due to no fault of the defendant and be serious enough to require the unlawful conduct. A common example is violating speeding and traffic laws to get someone gravely ill to the emergency room.

Duress Defense

Duress presents an excuse defense–the defendant acted only to prevent death or serious bodily harm to oneself or another. The perceived threat must be well-grounded and not caused by the defendant's own recklessness or negligence. Duress cannot generally be used to defend against murder charges.

The duress defense is classic movie material–the defendant hands over secret government documents to prevent their family members from being killed.

Involuntary Intoxication

Voluntary intoxication is not an affirmative defense. It can only be used (sometimes) to show a lack of specific intent and reduce the charges.

Involuntary intoxication, on the other hand, can generally be used as an affirmative defense, but only if the defendant shows credible evidence that the introduction of an intoxicant was unknown to them or the effects were beyond their control. A typical example would be having a drug slipped into one's drink unknowingly. If the drugged victim does something criminal while intoxicated, that person could argue they shouldn't be found criminally liable for their actions.

Entrapment

Entrapment can be a risky defense, as it's a tough one to get past jurors. The defendant must convince the factfinder that government actors unfairly induced them to commit the crime and they are not predisposed to criminal activity. For instance, a court allowed a defendant to present proof that his former lover induced him into arranging a drug deal in order to prove his love for him. It was revealed the former lover actually had a plea deal with the government to produce drug trafficking cases.

Statutes of Limitations

The running of the statute of limitations stops a criminal case in its tracks. This defense represents a policy decision to prevent the government from delaying a long time to charge someone. Shorter limitation periods generally apply to misdemeanor and non-violent offenses. Felonies tend to have longer time limits.

Specialized Defenses

States can provide specialized affirmative defenses that apply only to one crime. For instance, a state's mandatory child abuse reporting law might provide an affirmative defense if the mandatory reporter knew someone else reported the abuse. Sometimes these affirmative defenses reduce the potential punishment. A joyriding statute, for example, might reduce the penalties from a felony to a misdemeanor if a defendant abandoned the vehicle undamaged within a certain time frame.

Insanity Defense

While insanity defenses are rare, this defense represents an excuse from culpability due to the defendant being unable to understand the nature of their criminal behavior. This may lead to a not-guilty verdict, but the defendant won't go free. Rather, the defendant can end up institutionalized for much longer than any criminal sentence would have been.

How Defendants Prove Affirmative Defenses?

Just as states aren't consistent with what's considered an affirmative defense, they also differ on how an affirmative defense is raised or proven. For the most part, the defendant must raise the issue of an affirmative defense and present proof to support the defense.

Raising Affirmative Defenses

Certain affirmative defenses, such as insanity, must be raised by the defense through a special pleading to the court. More commonly, a defendant must present some "credible evidence" of a defense, regardless of whether the evidence comes in through the defendant or the prosecution. For instance, if the prosecution puts a witness on the stand who says the victim threw the first punch in a fight, the defendant might argue they acted in self-defense.

Proving Affirmative Defenses

Generally speaking, the defendant must prove their affirmative defense by a preponderance of the evidence (a more-likely-than-not standard). Some states require only that the defendant provide some evidence and then shift the burden to the prosecutor to disprove the affirmative defense beyond a reasonable doubt (a near-certainty standard). If a statute doesn't specify who has the burden, court decisions may provide guidance.

Affirmative Defense Cannot Negate an Element of the Crime

The law cannot (or, at least, should not) require the defendant to disprove an element of the crime itself. Defendants don't need to prove their innocence—they are presumed innocent. Requiring this type of action on the part of the defendant (disproving a criminal element) would unconstitutionally shift the burden of proof from the government to the defendant.

(Colo. Rev Stat. § 18-1-407; N.Y. Pen. Law § 25.00 (2025).)

Working With Your Lawyer

Here's the tricky part of affirmative defenses. Defendants usually offer an affirmative defense only when they have more or less conceded that the prosecution can prove or has proven all of the elements of the crime—which means a choice will likely need to be made between a failure-of-proof strategy or an affirmative defense. It's important to talk to your lawyer to determine if raising an affirmative defense is your best defense option.

There's a reason why the old line, taken from a closing argument, elicits laughter: "Ladies and gentlemen, you must acquit! My client wasn't there! If he was there, he didn't mean to do it! If he was there and meant to do it, he's crazy!"