Affirmative Defense

Definition

This is a defense in which the defendant introduces evidence, which, if found to be credible, will negate criminal liability or civil liability, even if it is proven that the defendant committed the alleged acts.

Overview

Self-defense, entrapment, insanity, necessity, and respondeat superior are some examples of affirmative defenses. 

Under the Federal Rules of Civil Procedure Rule 56, any party may make a motion for summary judgment on an affirmative defense. 

There is some dispute as to whether certain defenses are actually affirmative defenses, or just standard defenses. For example, in Campbell v. Avuff-Rose Music, Inc., 510 U.S. 569 (1994), the Supreme Court labeled fair use as an affirmative defense. However, as this University of Washington Law Review article details, it is unclear as to whether fair use is actually an affirmative defense. 

Further Reading

For more on affirmative defenses, see this University of Michigan Law Review article, this Chapman Law Review article, and this Federal Courts Law Review article