Insanity Defense

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Book Chapter

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Legal insanity is a complete defense to a criminal charge (see Criminal Law). Crimes are defined by their criteria, what lawyers call the “elements” of the crime, which the prosecution must prove beyond a reasonable doubt. These usually include an intentional act and a further mental state, called the mens rea. For example, murder is defined generally as the intentional killing of a human being. The prosecution must prove that the defendant intentionally performed a killing act with the intent to kill. Even if the prosecution is able to prove the elements beyond a reasonable doubt, however, a criminal defendant can avoid conviction by establishing an “affirmative” defense of justification or excuse. Many jurisdictions permit placing the burden of proof for legal insanity on the defense, a procedural rule that disadvantages defendants and may be more outcome determinative than the wording of the test for legal insanity.

Publication Title

The International Encyclopedia of Ethics