According to Wikipedia (links in the original), “An affirmative defense to a civil lawsuit or criminal charge is a fact or set of facts other than those alleged by the plaintiff or prosecutor which, if proven by the defendant, defeats or mitigates the legal consequences of the defendant’s otherwise unlawful conduct.” By way of example, Rule 8 of the Federal Rules of Civil Procedure (see here) contains a laundry list of 18 affirmative defenses, including laches, duress, and estoppel, just to name a few. (Oddly, two important legal defenses, those of mistake and necessity, are not included.)

What neither Wikipedia nor Rule 8 tell us, however, is, Where do these defenses come from? As it happens, one of my sabbatical projects this fall is to write up an essay with attorney Derrick M. Valkenburg exploring the natural law origins of Anglo-American common law affirmative defenses in law cases, so stay tuned!