The History of the Insanity Defense

The insanity defense is one of the more well known subjects pertaining to forensic psychology and the relationship between the mentally ill and the law. The simple fact that there is a distinction between those who commit a crime as a symptom of a mental disease and those who commit one for different reasons is a strong case for its importance in the understanding of Forensic Psychology.

Popular Conception and Misconception

All too often it is seen as an easy way out of jail-time, however this is simply not the case. A defendant who receives a ‘Not Guilty By Reason of Insanity’ verdict (NGRI) spends more time in confinement than they would have from a simple guilty verdict. Another misconception is that it is tried constantly. This is simply not true. Less that one percent of cases (0.85%) see an attempt at an insanity defense. Only about 0.26% are actually successful.



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Through history, various definitions of insanity as it relates to the criminality of conduct have existed. This section will look at three of them and the cases and social forces that led to each. While the transition from one to another is never immediate nor absolute, the broad strokes of change will be covered.

From ‘Punishing the Insane: The Verdict of Guilty But Mentally Ill’ : ‘Law does not exist in a vacuum, but is usually an expression of the underlying ethic of the sovereign. The insanity defense represents a necessary conflict between two fundamental American values: justice for criminals and compassion for the ill.’

An interesting link for criticism of the insanity defense:


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