The M’Naghten insanity defense, also called the right-wrong test, is the most common insanity defense in the United States. It is also the oldest and was created in England in 1843. The defense is named after Daniel M’Naghten. M’Naghten was under the paranoid delusion that the Prime Minister of England, Sir Robert Peel, was trying to kill him. When he tried to shoot Sir Peel from behind, he inadvertently shot Sir Peel’s Secretary, Edward Drummond, who thereafter died. M’Naghten was put on trial for murder and, to the shock of the nation, the jury found him not guilty by reason of insanity. 1 After a public outcry at this verdict, the British House of Lords developed a test for insanity that remains relatively intact today.
The M’Naghten insanity defense is cognitive and focuses on the defendant’s awareness, rather than the ability to control conduct. The defense requires two elements. First, the defendant must be suffering from a mental defect at the time he or she commits the criminal act. The mental defect can be called a “defect of reason” or a “disease of the mind,” depending on the jurisdiction. 2 Second, the trier of fact must find that because of the mental defect, the defendant did not know either the nature and quality of the criminal act or that the act was wrong.
The terms “defect of reason” and “disease of the mind” can be defined in different ways, but in general, the defendant must be cognitively impaired to the level of not knowing the nature and quality of the criminal act, or that the act is wrong. Some common examples of mental defects and diseases are psychosis, schizophrenia, and paranoia.
Jurisdictions vary as to the level of awareness the defendant must possess. Some jurisdictions use the term “know,” or “understand,” 3while others use the term “appreciate.” 4 If know or understand is the standard, the trier of fact must ascertain a basic level of awareness under the attendant circumstances. If appreciate is the standard, the trier of fact must analyze the defendant’s emotional state, and evidence of the defendant’s character or personality may be relevant and admissible.
A defendant does not know the nature and quality of a criminal act if the defendant is completely oblivious to what he or she is doing. This is quite rare, so most defendants claiming insanity choose to assert that they did not know their act was wrong. However, jurisdictions differ as to the meaning of “wrong.” Some jurisdictions define wrong as “legally wrong,” meaning the defendant must be unaware that the act is against the law. 5 Others define wrong as “legally and morally wrong,” meaning the defendant must also be unaware that the act is condemned by society. 6Generally, the only instance where the defendant must be “morally wrong,” standing alone, is when the defendant claims that the conduct was performed at the command of God, which is called the deific defense. 7 Whether the standard is legally wrong or morally wrong, if there is any evidence of a cover-up or an attempt to hide or escape, it is apparent that the defendant knew the difference between right and wrong, defeating the claim of insanity under M’Naghten.
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