Legal Dictionary

affirmative defense

Definition of affirmative defense


affirmative defense (plural affirmative defenses)

  1. (law) A defense against a suit or criminal charge that asserts mitigating facts rather than contesting the main fact of the allegation.

Further reading

An affirmative defense is a category of defense used in litigation between private parties in common law jurisdictions, or, more familiarly, a type of defense raised in criminal law by the defendant. Affirmative defenses can be classified as either a justification defense or an excuse defense. Affirmative defenses operate to limit, excuse or avoid a defendant's criminal culpability or civil liability, even though the factual allegations of the plaintiff's claim are admitted or proven. In fact, the defendant usually must affirm that the facts asserted by the plaintiff are correct in asserting his own defense; hence, "affirmative" defenses.

A clear illustration of an affirmative defense is self-defense. In its simplest form, a criminal defendant may be exonerated if he can demonstrate that he had an honest and reasonable belief that his conduct was necessary to protect himself from another's use of unlawful force.

"Mistake of fact" is another affirmative defense, usually used in combination with another, in which the defendant asserts that he reasonably believed the culpable act was necessary based on his observation, although, when given complete knowledge of the situation, it is clear that the act was unwarranted. Self-defense is still valid even if the defendant mistakenly believed he was in imminent danger of harmful or offensive bodily contact.

Among the most controversial affirmative defenses is the insanity defense, whereby a criminal defendant, shown to be insane at the time of his crime, seeks commitment to a mental institution in lieu of imprisonment.

Most affirmative defenses must be timely pled by a defendant in order for the court to consider them, or else they are considered waived by the defendant's failure to assert them. The classic unwaivable affirmative defense is lack of subject-matter jurisdiction. What constitutes timely assertion is often itself the subject of contentious litigation.

Because an affirmative defense requires an assertion of facts beyond those claimed by the plaintiff, generally the party making an affirmative defense bears the burden of proof. The burden of proof is typically lower than beyond a reasonable doubt. It can either be proof by clear and convincing evidence or a preponderance of the evidence. In some cases or jurisdictions, however, the defense must only be asserted, and the prosecution has the burden of proving beyond a reasonable doubt that the defense is not applicable.

Rule 8 of the Federal Rules of Civil Procedure governs the assertion of affirmative defenses in civil cases filed in the United States district courts. Rule 8(c) specifically enumerates the following defenses: "accord and satisfaction, arbitration and award, assumption of risk, contributory negligence, discharge in bankruptcy, duress, estoppel, failure of consideration, fraud, illegality, injury by fellow servant, laches, license, payment, release, res judicata, statute of frauds, statute of limitations, waiver, and any other matter constituting an avoidance or affirmative defense."

An affirmative defense is different from a negating defense. A negating defense is one which tends to negate an essential element of the state's case. Examples include voluntary intoxication and diminished capacity. The defendant does not have any burden of persuasion with regards to a negating defense. At most the defendant has the burden of producting sufficient evidence to raise the issue.


  1. Wiktionary. Published under the Creative Commons Attribution/Share-Alike License.


1.     lex situs
2.     lex causae
3.     lex loci delicti commissi
4.     lex loci celebrationis
5.     lex domicilii
6.     Clayton's Case
7.     AORO
8.     Miranda warning
9.     lex patriae
10.     defence of property