The Insanity Defense

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Each state, and the District of Columbia, has its own statute outlining the standard for determining whether a defendant is legally insane, therefore not responsible, at the time the crime is committed.

“An insanity defense is based on the theory that most people can choose to follow the law; but a few select persons cannot be held accountable because mental disease or disability deprives them of the ability to make a rational / voluntary choice. Such individuals need special treatment as opposed to prison; punishment is not likely to deter future antisocial conduct of these mentally diseased individuals.” Retrieved on 5/25/2010 from

There are basically two categories, the M’Naghten Rule and the American Law Institute Model. The states are pretty much split between these two categories, with the exception of Montana, Idaho, and Utah which do not allow for an insanity defense.

The M'Naghten Rule provides as follows:

"Every man is to be presumed to be sane, and ... that to establish a defense on the ground of insanity, it must be clearly proved that, at the time of the committing of the act, the party accused was laboring under such a defect of reason, from disease of mind, and not to know the nature and quality of the act he was doing; or if he did know it, that he did not know he was doing what was wrong."

Retrieved on 5/21/10 from

The test used under the M’Naghten standard, commonly referred to as the "right/wrong" test, to determine if a defendant can distinguish right from wrong is based on the idea that the defendant must know the difference of each...

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Works Cited

Knowles, Brian (2000). Is the Insanity Plea Allowing Criminals to Avoid Justice? Retrieved on 5/25/2010 from

Montaldo, Charles (n.d) The Insanity Defense; Standard for Legal Insanity Has Shifted. Retrieved on 5/19/2010 from

The "M'Naghten Rule" (n.d.) Retrieved on 5/21/10 from

Evolution of the Insanity Plea (n.d). Retrieved on 5/25/2010 from
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