An affirmative efense 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. There are three areas of offense: justifications, excuses, and alibi. A defendant affirms a criminal act is justified under certain circumstances that are presented, i.e. self defense, defense of others, defense of home/property. A defendant affirms a criminal act is excused due to a mental disease or defect at the time of the crime. A defendant affirms an alibi when it is impossible that the accused committed the crime due to the fact that the defendant was not present when it took place.Affirmative defenses operate to limit, excuse or avoid a defendant's criminal culpability or civil liability, even though the factual allegations of plaintiff's claim are admitted or proven.