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. Many affirmative defenses can be classified as justification defenses, or excuse defenses.[1] Affirmative defenses operate to limit, excuse or avoid a defendant’s criminal culpability or civil liability, even if the facts of the plaintiff’s claim are admitted or proven. In fact, the defendant usually must affirmatively come forward with some evidence that the defense exists; hence, “affirmative” defenses.

A clear illustration of an affirmative defense is self-defense.[2] 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 not an affirmative defense as it does not require to be proved to any expressed level but is used to introduce doubt. In mistake of fact defenses the defendant asserts that his mistaken belief prevents the required mens rea element from being established beyond a reasonable doubt. It can be used in combination with other defenses such as self-defense. Self defense would still be available even if the defendant’s belief that he was in imminent danger of harmful or offensive bodily contact was mistaken.

Among the most controversial affirmative defenses is the insanity defense,[3] whereby a criminal defendant seeks to be excused of criminal liability on the ground that an illness operating on his mind at the time of the alleged crime prevented him from understanding the nature of his actions or the wrongfulness thereof.

Most affirmative defenses must be pled in a timely manner 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.[4] The standard 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.[citation needed]

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.”

Rule 11 of the Federal Rules of Civil Procedure requires that affirmative defenses be based on “knowledge, information, and belief, formed after an inquiry reasonable under the circumstances,” and cannot consist of a laundry list of all known affirmative defenses.[5]

An affirmative defense can be different from a negating defense. A negating defense is one which tends to negate an essential element of the state’s case. An example might be a mistake of fact claim in a prosecution for intentional drug possession, where the defendant asserted that he or she mistakenly believed that the object possessed was an innocent substance like oregano. Because this defense simply shows that an essential element of the offense is not present, the defendant does not have any burden of persuasion with regards to a negating defense. At most the defendant has the burden of producing sufficient evidence to raise the issue.

The diversion is much different from a differed sentence in that if you fail to complete the diversion the case starts at the beginning and you still have all your rights to take the case to trial whereas with a differed sentence you usually do not retain this right.

At some point in late 2010 the City of Boulder will begin prosecuting MIP under the Boulder City ordinance 5-7-4 (see the Boulder MIP law). This decision is the result of Boulder City Council meeting on August 8, 2010 (see the agenda item). This is not good news because under the Boulder City ordinance the religious and parental exemptions that exist in Colorado MIP law have been removed. There is still a 911 exemption for up the three people under the Boulder City MIP ordinance.