Each week we select a legal term or phrase that’s commonly misunderstood, interesting, or could prove a matter of life-or-death to our readers (perhaps in some sort of deadly legal-trivia type situation).

Written by: Jeff W. Richards
An affirmative defense is a legal strategy used by defendants in which they admit to the case against them, but offer an excuse, justification, or rationale for their behavior that nullifies the criminal charges or civil liability they have incurred. In essence, this is the “Yeah, I did it, but it’s not my fault!” defense. When an affirmative defense is offered, the focus of the trial shifts from proving the facts underlying the complaint or charge to proving the facts underlying the defense.

Note that an affirmative defense typically shifts the burden of proof from the plaintiff to the defendant. This is because the defendant has effectively admitted their guilt in the lay sense of the word, and so need to prove that there are other facts that excuse their actions. The degree of proof the defendant will have to offer will depend on the circumstances of the case. The burden does not shift to the defendant in all circumstances. Especially since the turn of the century, there has been a shift toward requiring the prosecution to prove every element of its case, including proving that an affirmative defense does not apply.

Affirmative defenses can be either substantive or procedural. As an example, substantive affirmative defenses include Self-Defense, Insanity, or Duress. These defenses address the “substance” of the charges by contesting the facts. Examples of procedural affirmative defenses include asserting Statute of Limitations or Estoppel. These defenses deal with the procedural rules for bringing claims in court.

Not all affirmative defenses are perfect. While some things, such as self-defense, are absolute defenses, others, such as provocation, offer only partial defenses. A successful partial defense can reduce the severity of the charges, such as reducing murder to manslaughter.

There are several forms of defense other than the affirmative defense. Any defense that attacks the facts making up the case or complaint against the defendant are not affirmative defenses. Examples of these include alibis, impeaching the credibility of witnesses, or otherwise attacking the evidence presented by the plaintiff or prosecution.