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This paper reviews the various ways in which an offender's mental illness can have an effect on liability and offense grading under American criminal law. The 52 American jurisdictions have adopted a variety of different formulations of the insanity defense. A similar diversity of views is seen in the way in which different states deal with mental illness that negates an offense culpability requirement, a bare majority of which limit a defendant's ability to introduce mental illness for this purpose. Finally, the modern successor of the common law provocation mitigation allows, in its new breadth, certain forms of mental illness as a murder mitigation, mitigating to a lesser form of murder or to manslaughter.


Insanity, mental illness negating offense element, provocation, extreme mental or emotional disturbance, diminished capacity, partial insanity, American criminal law codification, psychology, competence, responsibility, culpability, mitigation

Publication Title

Northern Ireland Legal Quarterly

Publication Citation

65 Northern Ireland Legal Quarterly [NILQ] 229 (2014)