10 CL & F. 200, 8 Eng. Rep. 718 (1843)
M'Naghten believed that he was
the victim of an international conspiracy, involving the Pope and the
British Tory government. He went to London and shot a guy he thought was
the Prime Minister.
M'Naghten was arrested and
charged with murder.
The British Trial Court found
M'Naghten not guilty by reason of insanity.
M'Naghten was then forcibly
institutionalized for the remainder of his life under the Criminal
Lunatics Act of 1800.
The case caused a public
outcry in England. The House of Lords sat down and developed a set of
rules (known as the M'Naghten Rules)
for when insanity can be used as a defense. These rules
Presumption of Sanity:
Sanity is a rebuttable
presumption and the burden of proof is on the party relying upon it; the
standard of proof is on a balance of probabilities, that is to say that
mental incapacity is more likely than unlikely.
Disease of the Mind:
It doesn't have to be a
'brain' condition, it could be "any disease which produces a
malfunctioning of the mind." But it must be a 'disease', the
defense can't be used if you just get carried away.
Nature and Quality of the
The defense of insanity covers situations where the defendant doesn't
understand what they a physically doing.
Knowledge that the act was
The defense of insanity covers situations where the defendant knows
what they are doing, but can't understand that it is a criminal act.
Insanity is not a defense for crimes of strict
This case laid out the basic
common-law principles for the defense of insanity.
The M'Naghten Test is just a cognitive test. It says that a
defendant is not responsible for his criminal conduct if, at the time of
the conduct, as a result of a mental disease or defect that he:
Did not know the nature and
quality of the act he was doing, or
Did not know what he was
doing was wrong.
The Model Penal Code §4.01 test has a both a cognitive prong and a
volitional prong. It says that a defendant is not responsible for his
criminal conduct if, at the time of the conduct, as a result of a mental
disease or defect, he lacked substantial capacity to:
Appreciate the criminality
(aka wrongness) of his conduct, or
Conform his conduct to the
requirements of the law.
So, a kleptomaniac who
knows that stealing is wrong, but can't help himself, would be entitled
to an insanity defense under the Model Penal Code, but not under M'Naghten