UPDATED: June 19, 2018
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With an affirmative defense, the defendant admits guilt to committing the crime, but uses an affirmation defense to introduce additional facts or explanation to justify his or her conduct. Some of the most common affirmative defenses include mental illness, self-defense, entrapment, mistake of fact, intoxication, duress. If defendant successfully offers a justification for his or action or behavior, his legal liability is limited or completely exonerated.
Affirmative vs. Negating Defenses
An affirmative defense is used to explain or justify the behavior that is alleged to be criminal. But this defense can sometimes be more difficult to prove than a negating defense. A negating defense attacks an essential element of the criminal charge brought by the prosecutor. Because the prosecutor has the initial burden of proving every element of a crime beyond a reasonable doubt, to negate, the defense only has the burden of creating doubt about one or all of the elements. To do so, the defendent has to produce some actual evidence through eyewitnesses, videos, or other physical proof to support justification.
However, the use of an affirmative defense is not about attacking an element of the crime, it is usually about justifying or excusing the criminal action. For example, suppose a defendant is on trial for first degree murder of her husband. To prove a first degree murder charge, the prosecutor must generally offer evidence that the murder was premeditated, that is, the defendant planned the murder beforehand. The prosecutor has plenty of DNA evidence to connect the defendant to the murder of her husband, but weak or speculative evidence that the defendant actually planned the murder. The defense may use a negating defense in this case, to show that since the prosecution has not proved beyond a reasonable doubt that the defendant planned to kill her husband, the jury cannot convict the defendant for first degree murder.
However, to strengthen the case that the murder was not premeditated, the defense may also introduce additional evidence which shows that the defendant acted in self-defense. This additional evidence may be photos of the defendant after the murder which shows her badly beaten, or witness testimony that someone heard the defendant crying out for help the night of the murder. Self-defense is a commonly used affirmative defense, which justifies a defendant’s unlawful behavior on the basis of protecting oneself. If used successfully, the defendant in this case could be exonerated of the crime altogether.
Types of Affirmative Defenses
While the availability of an affirmative defense will depend on the state, there are generally two categories of affirmative defenses, justifications and excuses. There is also one affirmative defense that defendants use when they deny the charge altogether, called the alibi defense.
Justification defenses say that, though the defendant did the crime, there were very good reasons for doing so. The above example in which the defendant used self-defense as a justification for killing her husband is an example of this type of affirmative defense. Other justification defenses include defense of property, defense of others, law enforcement defense, and necessity.
Excuse defenses assert an excuse for committing the crime, even though the defendant admits to committing the crime. Excuse defenses include insanity, duress, diminished capacity, intoxication, and infancy. For example, a defendant who uses the insanity defense alleges that though he committed the crime, he was unable to know right from wrong as a result of his mental illness, and therefore he could not control his behavior at the time of the crime and should be excused. Similarily, a defendant who asserts that he committed the crime under duress, is admitting to committing the crime, but because he was forced to commit the crime (i.e., robbing a bank because the wife was hostage if you did not), it was out of his control and should be excused.
Finally, an alibi affirmative defense is probably the best affirmative defense because the defendant maintains his complete lack of involvement with the crime. An alibi defense offers evidence that the defendant was not at the scene of the crime when the crime took place. An alibi affirmative defense is most effectively used in conjunction with a negating defense. For instance, if the prosecutor has weak evidence that tends to show that the defendant was at the crime scene, the defense can point this weakness out as a negating defense, and also assert an alibi as an affirmative defense.