Law360 (August 3, 2026, 5:27 PM EDT) -- The Michigan Supreme Court has revived the diminished capacity defense in criminal cases, overruling a 25-year-old precedent that barred defendants from using evidence of mental illness short of legal insanity to challenge whether they acted with the intent required for a crime.

In a 6-1 decision issued Friday, the court ruled that Michigan's legal insanity statute does not prevent defendants from introducing mental health evidence to negate the specific-intent element of a charged offense.

The decision overturned the 2001 ruling in People v. Carpenter , in which the state high court held that evidence of mental incapacity short of insanity cannot be used to avoid or reduce criminal responsibility by negating specific intent.

"Today, we conclude that Carpenter was wrongly decided and that the principles of stare decisis weigh in favor of overruling it," Justice Richard H. Bernstein wrote for the majority, using the Latin term for the principle that courts follow legal precedent to ensure consistency.

The ruling is all but certain to spur a sharp increase in postconviction motions and appeals by defendants seeking diminished capacity evaluations. Gabrielle Barber, an assistant defender at the Michigan State Appellate Defender Office who represents Cinecca D. Madison, a man who was found competent to stand trial on charges of murder, assault with intent to commit murder and firearm possession, stemming from a fatal June 2022 shooting in Holland, Michigan, said the ruling was a "landmark" decision and anticipated that it will lead to many defendants invoking it in postconviction motions.

"By allowing people to raise a defense of diminished capacity, the Michigan Supreme Court has recognized how mental illness may contribute to a person's actions resulting in criminal offenses. The court has rightly recognized that people who commit offenses due to their mental illness may not be capable of forming the required intent to be found guilty," Barber said. "My hope is that, as the issue of the diminished capacity defense continues to be litigated, courts and attorneys treat the issue with the care and legal consideration it requires and deserves."

In a concurring opinion, Justice Noah Hood said overruling Carpenter will cause "a deluge of logistical, operational, and funding challenges" such as slower court proceedings and overburdened mental health facilities — but that it was the right decision.

As the sole dissenter, Justice Brian K. Zahra wrote in an opinion that the Carpenter ruling "has withstood the test of time" and that the majority's decision "undermines the expressed will of the Legislature" in crafting the statute.

Madison was 19 years old when he allegedly shot two companions while they were riding bicycles in a park, then fled the scene. Ten months before the shooting, he had experienced paranoia and hallucinations and was involuntarily taken to a hospital for a mental health evaluation. He was diagnosed with schizophreniform disorder, a precursor to schizophrenia.

Madison moved to introduce evidence that, although he was not legally insane, his mental illness prevented him from forming the specific intent — meaning acting with a particular purpose to cause a desired harm — required for the charged offenses.

At trial, his attorneys argued that his mental illness and intellectual limitations affected his perceptions, behavior and ability to form intent, known as mens rea, which is one of the four elements of a crime prosecutors must prove beyond a reasonable doubt to obtain a conviction.

The trial court, however, declined Madison's motion, citing the Carpenter ruling, which it said created an "all or nothing" insanity defense. The court concluded that because he didn't meet the definition of legal insanity, he was barred from using evidence of mental illness to negate mens rea.

Madison challenged the precedent on appeal, first unsuccessfully to the Michigan Court of Appeals, then to the high court.

Michigan's legal insanity statute, MCL 768.21a, allows defendants an opportunity to show, by a preponderance of the evidence, that they were "legally insane" when the offense occurred. The statute also makes clear that having a mental illness or intellectual disability alone is not enough to establish legal insanity, and that being intoxicated with alcohol or drugs doesn't create such a defense.

In overruling Carpenter on Friday, the Michigan Supreme Court said the justices who decided the older case "expended little effort" on interpreting the law's text and that their legal analysis "turns the canons of statutory interpretation on their head."

In the majority opinion, Justice Bernstein explained that a diminished capacity argument differs from an insanity defense. The insanity defense, he wrote, is an affirmative defense where a defendant admits guilt but seeks to excuse it without reference to any individual elements of the crime. On the other hand, a defendant uses diminished capacity evidence to deny specific intent, which is one of the elements.

"This approach does not admit the crime and seek to then excuse or justify it," Justice Bernstein wrote. "Instead, it challenges the prosecution's case by questioning whether a defendant had the requisite mens rea at the time of the crime."

Because these two approaches are different, the Carpenter court was wrong in assuming that the legal insanity statute also covered the use of diminished capacity evidence.

"The statute simply does not state or imply anything about the availability of diminished-capacity evidence to negate a specific element of a crime," Justice Bernstein wrote.

In considering whether to strike down Carpenter, the high court noted that overruling the precedent "will lead to a change" in the type of evidence that defendants will seek to raise at trial, but would not fundamentally alter the trial process. The majority also acknowledged Justice Hood's concerns, saying it was "possible" that overturning the decision could delay trials and burden court operations.

But the justices ultimately concluded that logistical challenges did not outweigh the implications for defendants, who were deprived of a defense that was long available before Carpenter was decided.

The court noted that Carpenter was increasingly at odds with evolving scientific understandings of mental health and intellectual disability.

It cited a March 2025 amicus brief in which the American Psychological Association, the Michigan Psychological Association and the National Association of Social Workers argued that treating mental illness as a series of diagnostic points along a spectrum from sanity to insanity does not reflect modern scientific understanding.

"It is not in the public interest for this court to bind lower courts to an incorrect interpretation of a legislative framework, especially when that framework is based on an evolving understanding of mental illness and other forms of mental incapacity," the majority concluded. "Carpenter's flawed interpretation of the legal-insanity statute cannot be permitted to stand."

The State of Michigan is represented by Ottawa County Prosecutor Sarah F. Matwiejczyk.

Madison is represented by ImeIme Umana and Gabrielle Barber of the Michigan State Appellate Defender Office.

The case is Michigan v. Madison, case number 167120, in the Michigan Supreme Court.

--Editing by Linda Voorhis.

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