Before the eighteenth century, insanity was considered a sickness rather than a mental disorder. It was a belief insane people were to be possessed by demons. Mentally ill people were treated as criminals for committing insane acts. Imprisonment, torture, and execution were the only treatment administered (Gado 1). It was not until 1843, in a Great Britain court against Daniel M"Naghten, proposals for changes to the methods of treating the mentally ill were looked at. This case provided the basis for legal decisions in American courts. In today's judicial system, the defendants are abusing this plead to escape serving prison terms and execution. .
Although, Daniel M"Naghten's attempt to murder British Prime Minister Robert Peel failed, it resulted in the murder of the Minister's secretary by mistake. M"Naghten was tried for murder; he pleaded for insanity. His attorney presented evidence that he suffered from psychotic delusions. Psychotic delusions are described as false, inaccurate beliefs the person holds onto even when he or she is presented with accurate information. The ruling of the trail was not guilty by reason of insanity. M"Naghten was acquitted of murder and committed to an asylum. The outcome of the trail resulted in a public outcry for an explanation of the court's decision. The members of the court were forced to explain the newly established insanity law (Gado 2). The U.S. criminal justice system quickly adopted the legal precedent established by the M"Naghten decision, thus, the insanity defense was found.
The American Law Encyclopedia defines insanity defense plead as a defense asserted by an accused in a criminal prosecution to avoid liability for the commission of a crime because, at the time of the crime, the person did not understand the wrongfulness of his or her conduct due to a mental disease or defect (Guide 1). The definition was derived from the M"Naghten case.