08/14/2026
The Michigan Supreme Court has revived the doctrine of diminished capacity in People v. Madison, overruling its 2001 decision in People v. Carpenter.
For about 25 years, Carpenter barred defendants from using evidence of mental illness or impairment — short of legal insanity — to challenge whether they had the specific intent required for certain crimes.
Diminished capacity is not an insanity defense. It does not excuse criminal conduct; it addresses whether the prosecution has proven the required mental state.
Some offenses require specific intent, such as premeditation or intent to achieve a particular result. Under Carpenter, mental-condition evidence generally could not be used to dispute that element unless the insanity standard was met.
Madison changes that. Defendants charged with specific-intent crimes may now introduce relevant mental-condition evidence to argue the prosecution has not proven intent beyond a reasonable doubt, even if they are not legally insane.
The ruling does not create a defense to liability, but it restores the ability to use mental-condition evidence to challenge intent. Michigan courts will now again consider such evidence in appropriate cases, marking a significant shift in criminal law.