In our last post, we discussed a case where a man was found not guilty of a violent crime, after the jury found that he was acting in self-defense. In most states, self-defense is an affirmative defense to certain criminal charges.
An affirmative defense gives criminal defendants the right to acknowledge that they committed the acts the prosecutor claims they did, while also providing an explanation that excuses those actions. Affirmative defenses recognize that sometimes, a person is not in control of his or her actions.
Insanity is one form of affirmative defense. It is fairly well-known, given its frequent use as a plot device in TV and movie legal dramas. But what does it really mean to plead insanity in Michigan?
Different states use different standards that defendants must meet to show they were legally insane at the time of the alleged crime. Michigan law requires the defendant to show that he or she lacked "substantial capacity either to appreciate the nature and quality or the wrongfulness of his or her conduct" due to a mental illness or intellectual disability.
The roots of the insanity defense in the U.S. go back to the British legal history. A 1581 legal treatise from England ruled that a "madman or a natural fool, or a lunatic" cannot be punished for killing someone. Later, in the 18th Century, British courts developed the "wild beast" test, in which a person accused of a crime could not be convicted if he or she did not understand the crime better than "an infant, a brute, or a wild beast."
Today, we naturally abhor using such derogatory terms when discussing mental illness. But the principle that a person who did not understand what he or she was doing due to an illness should not be held accountable for his or her actions remains the law.