When does insanity excuse criminal liability?

A defendant has an excuse for liability, says Paul Robinson, in his book Criminal Law Defenses, when he or she is acting involuntarily and their own disability causes him or her to mistakenly or unknowingly violate a criminal prohibition. This person does not know whether his or her behavior is wrong or criminal (Robinson 222). This is in contrast to what is called a character-based approach, where a person's adherence to virtues or vices creates a character and a reputation for morality or immorality, upon which they are judged. Finkelstein argues that a system which bases its retributive punishment on a person's character, rather than on the act itself brings about social welfare. Just as one cannot judge a person's moral character upon a single act, one cannot decide the morality or immorality of a person by visible actions. She quotes George Fletcher as...
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