A defense that accepts the basic accusation for argument's sake but adds new facts or law that can defeat or limit liability or guilt.

"Affirmative" matters because the person raising it usually has to do more than simply deny the claim. Instead of saying, "that never happened," the argument is closer to, "even if it happened, there is a legal reason I should not lose." In a criminal case, examples can include self-defense, duress, insanity, or entrapment. In a civil case, common affirmative defenses include comparative fault, assumption of risk, or the statute of limitations. The details matter because these defenses often have to be stated early in the case, usually in the answer or other formal pleading, or they can be limited or waived.

Practically, an affirmative defense can completely change the direction of a case. It affects what evidence each side looks for, what witnesses matter, and who carries the burden of proof on particular issues. A case that looks straightforward at first can turn on whether the defense can prove those added facts.

For injury claims in Iowa, comparative fault is a major affirmative defense. Under Iowa's modified comparative fault rule in Iowa Code chapter 668, a person cannot recover damages if they are more than 50 percent at fault - the 51 percent bar. If they are 50 percent or less at fault, damages are reduced by that percentage.