Criminal defenses

Law checked as of 11 November 2026 · Written by the criminallaw.wiki editorial team

A criminal defense is any argument or set of facts a defendant raises to avoid conviction. Some defenses simply attack the prosecution's proof, while others—called affirmative defenses—introduce new evidence that can defeat liability even if the prosecution proves its case.^[1]Common categories include justification defenses such as self-defense and necessity, and excuse defenses such as insanity and duress.^[2][3][4][5]

Overview

Criminal defenses are the legal and factual arguments a defendant can use to avoid or reduce criminal liability. Some defenses challenge whether the prosecution has proven the elements of a crime, including the required mens rea, while others—affirmative defenses—add new facts that can defeat liability even where the defendant committed the alleged acts.^[1]Affirmative defenses are further divided into justification defenses, which argue the conduct was the right thing to do under the circumstances, and excuse defenses, which argue the defendant should not be held responsible despite the wrongful act.^[3][4]Rules on which defenses apply, and how they are classified, vary by state.^[1]

Failure-of-proof defenses

A defendant does not always need to introduce a special defense; sometimes the argument is simply that the prosecution has not met its burden on one of the basic elements of the charged offense. Commentary on affirmative defenses notes an ongoing dispute over whether certain defenses are truly affirmative defenses or are instead "standard defenses" that merely dispute the prosecution's proof.^[1]Because classification can affect who carries the burden of proof, the distinction can matter a great deal during a criminal trial.^[1]

Affirmative defenses

An affirmative defense is a defense in which the defendant introduces evidence that, if credible, will negate criminal liability even if the prosecution proves the defendant committed the alleged acts.^[1]The party raising an affirmative defense has the burden of proving it, and raising one does not prevent the defendant from also raising other defenses.^[1]Examples commonly treated as affirmative defenses include self-defense, entrapment, insanity, and necessity, though whether a specific defense counts as affirmative can differ by state—self-defense is affirmative in Florida but not in Ohio.^[1]Entrapment is one such affirmative defense, where a defendant argues that law enforcement or a state agent induced them to commit a crime they would not otherwise have committed; under the subjective test used in many jurisdictions, the defendant must show a lack of predisposition and that the government induced the conduct.^[6]

Justification defenses

Justification defenses argue that, given the circumstances, the defendant's conduct was the right or reasonable choice. Self-defense is a justification defense used in unlawful acts involving force, such as murder and assault and battery, and it requires an imminent danger, a proportionate response, and that the defendant was not the initial aggressor.^[2]The necessity defense is also a justification defense; it applies where illegal conduct was the lesser of two evils needed to prevent a more serious harm, and most jurisdictions require that the actor had no reasonable alternative and did not create a greater danger than the one avoided.^[3]

Excuse defenses

Excuse defenses do not claim the conduct was right; instead, they argue the defendant should not be held responsible because of their mental state or circumstances. The insanity defense is an affirmative defense in which the defendant admits the act but asserts a lack of culpability due to mental illness, commonly analyzed under tests such as the M'Naghten rule, which asks whether the defendant knew the nature of the act or that it was wrong.^[4]Duress is a related excuse defense in which unlawful threats or coercive behavior cause a person to commit an act they otherwise would not commit; the defendant must show the action was compelled by a reasonable threat of imminent death or serious bodily injury with no safe way to escape the threat.^[5]Necessity and duress are closely related but distinct: duress generally arises from another person's threats and negates the required mental state, while necessity arises from other circumstances and involves a choice between two unavoidable evils.^[3]

Procedural defenses

Procedural defenses do not dispute guilt directly; they argue that the case cannot proceed for a separate legal reason. One procedural issue closely tied to criminal responsibility is competency to stand trial: a defendant who is legally incompetent cannot be tried, and if a defendant is found incompetent, the question of insanity becomes moot until competency is established.^[4]Other procedural arguments, such as those based on the statute of limitations, raise separate legal bars to prosecution; rules on these issues vary by state. Anyone facing charges can ask a court-appointed or private attorney about available defenses, including through public defenders.^[4]

Entries in this section

Further entries planned for this section (not yet published):

• Justification vs excuse defenses
• Affirmative defenses and who must prove them
• Self-defense
• Stand-your-ground laws and the castle doctrine
• Defense of others
• Defense of property
• The insanity defense
• Competency to stand trial
• Diminished capacity
• Intoxication as a defense
• Duress
• Necessity
• Entrapment
• Mistake of fact and mistake of law
• Consent as a defense
• Alibi
• Infancy
• Challenging the evidence and reasonable doubt

Common questions

Related topics

• Elements of a crime
• Mens rea (the guilty mind)
• The criminal trial
• Murder
• Assault and battery
• Criminal statute of limitations
• Public defenders

References

All sources retrieved November 2026.

1. ^ ^{a b c d e f g h i j k l m n o} "Affirmative defense (Wex)". Legal Information Institute, Cornell Law School. Retrieved November 2026.
2. ^ ^{a b c d e} "Self-defense (Wex)". Legal Information Institute, Cornell Law School. Retrieved November 2026.
3. ^ ^{a b c d e f} "Necessity defense (Wex)". Legal Information Institute, Cornell Law School. Retrieved November 2026.
4. ^ ^{a b c d e f g h i} "Insanity defense (Wex)". Legal Information Institute, Cornell Law School. Retrieved November 2026.
5. ^ ^{a b c d e} "Duress (Wex)". Legal Information Institute, Cornell Law School. Retrieved November 2026.
6. ^ "Entrapment (Wex)". Legal Information Institute, Cornell Law School. Retrieved November 2026.