Insanity

Insanity is doing the same thing over and over again and expecting different results. And if the dam breaks open many years too soon And if there is no room upon the hill And if your head explodes with dark forebodings too I'll see you on the dark side of the moon

Insanity, when used properly in the fields of psychology, medicine, and law, is recognised as a behavior which displays beliefs or actions that fall outside of the "normal" recognition of society. Such actions can cause the person performing them to become a danger to themself or others. The term insanity is more frequently used in an incorrect form, often used in lieu of "abnormal", "unusual", or "crazy."

Legal and medical insanity
Despite popular misconceptions, "insanity" is obsolete as a medical term. The former usage of "insanity" encompassed disorders ranging from delusions to schizophrenia.

“Insanity” remains alive and well as a defense, however, in criminal law. In common law jurisdictions, jury instructions as to a defendant’s insanity emerged in their modern form from a case brought before the House of Lords (yes, that one). There, the accused was one Daniel M’Naghten, a Scottish woodturner motivated by paranoid delusions of persecution in assassinating an English public servant. (The guy thought the government was out to get him.) From that case came the following standard for determining a criminal defendant’s insanity (emphasis added):

This rule can excuse the criminal acts of a defendant so long as that defendant suffered a cognitive defect or disease at the time he committed the criminal act. (You can’t, for example, pull a Raskolnikov, murder someone in cold blood, and then go crazy after the fact.) Other standards, however, place less emphasis on cognitive flaws, relying instead on establishing whether the defendant operated under some substantial volitional weakness. This is often called the irresistible impulse test. Under this test, a defendant can claim he knew right from wrong but just couldn’t help himself.

Half of U.S. states use some flavor of the M’Naghten rule. The rest have either abolished an insanity defense outright or use an alternative standard written by the American Law Institute in its 1962 Model Penal Code. The ALI–MPC insanity defense smashes together the cognitive component of the M’Naghten rule and the volitional component of the irresistible impulse test. The Code formulates the affirmative defense of insanity as follows (emphasis added, again):

Note the “or” in subsection 1. The disjunction allows a defendant to claim he operated under an intellectual flaw, and if that fails, to alternatively claim he knew right from wrong but otherwise suffered a defect in willpower. The ALI–MPC test allows a criminal defendant to get two insanity defenses for the price of one. Pretty forgiving.

Then came the trial of John Hinckley, Jr. You know, the guy who watched too much Taxi Driver and wanted to impress Jodie Foster by assassinating Asmodeus in human form Ronald Reagan. Hinckley’s trial for attempting to kill the president was held in federal court, which used the very forgiving ALI–MPC test. Unsurprisingly, Hinckley got off after having been found not guilty by reason of insanity. Public outrage ensued, pressuring many U.S. states to either outright abolish the insanity defense or go back to a version of M’Naghten.

Be warned, dear reader, that pleading insanity is typically a very bad idea. Successfully using the insanity defense won’t send you to prison, but it will send you somewhere far worse: civil mental institutions. If you’re found not guilty by reason of insanity, the state can civilly commit you until you can convince a judge to let you go. Hinckley himself was kept in a psychiatric hospital for 35 years after his trial concluded.