When mental illness isn't insanity: psychiatric evidence and the question of intent

A recent decision out of Michigan looks at a common question forensic psychiatrists deal with: what happens when a defendant has a real, documented psychiatric illness, but that illness doesn't rise to legal insanity?

In July 2026, the Michigan Supreme Court decided People v. Madison, No. 167120 (Mich. July 31, 2026), overruling People v. Carpenter, 464 Mich 223 (2001), a 25-year-old precedent that had generally barred defendants from using mental incapacity short of insanity to challenge the specific intent required for a crime. The defendant, 19 at the time, had a documented history of paranoia, hallucinations, and schizophreniform disorder, and evaluators had concluded he was mentally ill but not legally insane. A six-justice majority held that Michigan's insanity statute, MCL 768.21a, does not categorically prevent a defendant from introducing this kind of evidence to challenge the prosecution's proof of mens rea.

Madison puts a sharp point on a question that comes up in this work far more often than legal insanity itself does: whether a defendant's mental illness, even though it falls short of legal insanity, is still relevant to what he perceived, believed, intended, or understood at the time of the alleged offense. Whether the law permits that evidence to be used to negate mens rea, however, depends heavily on the jurisdiction, and, for anyone practicing in California, the answer has actually been settled for more than four decades, under different vocabulary than Michigan just adopted.

Legal Insanity and Mens Rea Ask Different Questions

Legal insanity is generally an affirmative defense. Although the standards vary by jurisdiction, the question typically concerns whether a mental disorder impaired a legally defined capacity, such as appreciating the wrongfulness of conduct.

Mens rea concerns an element of the charged offense. Depending on the crime, the prosecution may have to prove that the defendant acted intentionally, knowingly, willfully, maliciously, or with some other specified mental state.

Those inquiries may involve some of the same psychiatric evidence, but they are not interchangeable. A defendant with schizophrenia, for example, may retain enough understanding to fall outside the jurisdiction's insanity standard while simultaneously experiencing delusions that are relevant to whether the prosecution can prove a particular intent beyond a reasonable doubt. That was essentially the distinction at issue in Madison: the defense did not contend the defendant was legally insane, only that his psychiatric condition affected his ability to form the specific intent required for the charged crimes.

What Is "Diminished Capacity"?

The terminology can be confusing.

"Diminished capacity" is often used to describe the use of evidence of mental illness, cognitive impairment, or another mental condition to challenge whether a defendant actually possessed the mental state required for a particular offense. It is not necessarily an affirmative defense in the same way as legal insanity. Instead, the evidence may be offered to challenge the prosecution's proof of an element of the crime.

That distinction has a practical consequence. Negating the specific intent required for one offense does not necessarily mean acquittal of all criminal liability. A defendant may still be convicted of a lesser or related offense that does not require the same specific intent.

A Diagnosis Does Not, By Itself, Negate Intent

The existence of schizophrenia, bipolar disorder, intellectual disability, traumatic brain injury, or another condition does not, by itself, establish what a person intended during a particular act.

A forensic psychiatrist assesses what symptoms were present, what the defendant believed, how those symptoms affected perception or reasoning, and whether there is a meaningful connection between the psychiatric condition and the particular mental state required by the offense.

Consider a defendant experiencing a persecutory delusion who shoots another person. If he believes he is shooting an innocent person because voices are telling him to do so, the psychiatric illness may bear on his intent and on any claim of legal insanity, but in different ways. If he genuinely believes the other person is an assassin who is about to kill him, the same diagnosis may have a very different relationship to his perception of the circumstances and his reason for acting. And if the defendant has schizophrenia but the offense was committed for reasons unrelated to psychosis, the diagnosis may add little to the analysis of intent.

The diagnosis is only the beginning of the forensic inquiry.

Psychiatric Evidence Still Has to Be Connected to the Mental State at Issue

One concern in these cases is allowing evidence that a defendant was mentally ill to substitute for analysis of the actual element the prosecution must prove.

A psychiatric expert can describe symptoms, diagnosis, cognition, perception, and the likely effects of a disorder on mental functioning. Depending on the jurisdiction and evidentiary rules, the expert may also be able to explain how those findings bear on a specific mental-state question.

The usefulness of that testimony generally depends on how clearly the reasoning is tied to the specific element at issue. If the relevant offense requires an intent to kill, the psychiatric analysis should address how the identified symptoms relate to that intent. If the legal question involves premeditation, knowledge, or another mental state, the relevant analysis may be different. A broad statement that a defendant's "mental illness affected his judgment" may be clinically accurate without clearly addressing the legal question.

Even Where This Evidence Is Allowed, It Is Not a Free-For-All

Even where this kind of evidence is permitted, ordinary evidentiary limits still apply. The evidence must be relevant to the specific intent at issue, it may still be excluded if its limited value is substantially outweighed by risks such as confusion or unfair prejudice, and expert testimony remains subject to the jurisdiction's expert-evidence requirements. In her Madison concurrence, Chief Justice Cavanagh made exactly this point for Michigan, and it is a useful general caution regardless of where a case is pending.

There is a substantial difference between evidence demonstrating that a defendant had a psychiatric diagnosis and evidence helping a factfinder understand whether symptoms of that disorder actually affected the mental state required by the charged crime. Forensic psychiatrists are generally most useful in the second situation.

"Diminished Actuality": What California Already Allows

California has permitted a version of this evidence for more than four decades, under different vocabulary and narrower limits.

California abolished the common-law diminished capacity defense outright. Penal Code section 28, subdivision (b) states, as a matter of public policy, that "there shall be no defense of diminished capacity, diminished responsibility, or irresistible impulse in a criminal action." That abolition followed public reaction to how the defense had been used in the late 1970s, and it remains a firm rule.

However, Section 28, subdivision (a) provides that evidence of a mental disease, defect, or disorder cannot be offered to show that a defendant lacked the capacity to form a required specific intent, but remains admissible solely on whether the defendant actually formed a required specific intent, premeditated, deliberated, or harbored malice aforethought. Penal Code section 29.4, governing voluntary intoxication, is built on the same structure: no capacity argument, but evidence admissible solely on whether the defendant actually formed the required intent. Commentators sometimes describe this narrower, surviving concept as "diminished actuality" to distinguish it from the abolished capacity-based defense.

California law also imposes constraints that go further than the evidentiary limits described above. Penal Code section 29.2, subdivision (b) bars evidence that the accused lacked the capacity or ability to control his or her conduct when offered on the issue of whether the accused actually had the mental state required for the crime. And Penal Code section 29 prohibits an expert from testifying whether the defendant did or did not have the required mental state at all; that question is reserved for the trier of fact. A California forensic evaluator can describe the diagnosis, the reported symptoms, and how those symptoms may affect perception, reasoning, deliberation, or other aspects of mental functioning, but the final inferential step, whether this particular defendant actually harbored the required mental state, is for the jury.

The same diagnosis and the same reported symptoms can be presented very differently to a jury in Michigan than to a jury in California, and an evaluator who does not track that difference risks offering testimony the jurisdiction does not permit the jury to hear.

The Evidence Is Often Retrospective

An evaluation concerning mens rea often occurs months or years after the alleged offense. The evaluator may consider contemporaneous psychiatric records, witness accounts, statements by the defendant, electronic communications, police observations, substance use, medication history, and behavior before and after the event.

Later evaluations can also provide useful information, but a diagnosis made after an offense does not, by itself, establish the defendant's condition at the earlier time. Longitudinal records can be particularly useful in determining whether similar symptoms existed before the offense and how the defendant's condition changed over time.

The Rules Differ Substantially by Jurisdiction

Perhaps the most important practical point is that there is no single national rule governing psychiatric evidence and mens rea. Michigan itself demonstrates how dramatically the law can change: from Carpenter in 2001 until Madison in 2026, Michigan generally barred this kind of evidence, and its highest court has now reversed that position. California, discussed above, took a different path decades ago, permitting evidence bearing on whether a defendant actually formed a required mental state while expressly prohibiting anything labeled a capacity-based defense. Other states restrict this kind of evidence far more substantially, and some largely exclude it. In Clark v. Arizona, 548 U.S. 735 (2006), the United States Supreme Court recognized substantial state authority to determine how mental-disease evidence may be used in criminal cases, upholding Arizona's decision to channel such evidence into the insanity determination rather than allowing it to negate mens rea directly.

That is what makes a case like Madison worth watching, not because it changes the rule everywhere, but because it is a reminder of how much the underlying analysis, and the vocabulary used to describe it, varies by jurisdiction. Before translating psychiatric findings into an opinion relevant to intent, the evaluator needs to understand what mental state matters, what psychiatric evidence the jurisdiction permits the factfinder to consider, and what the jurisdiction's rules allow the expert to say about it directly.

Disclaimer: This article is provided for general educational and informational purposes only and reflects discussion of forensic psychiatric issues, not legal or medical advice. The significance of psychiatric evidence depends on the facts of the individual case, the applicable legal standard, and the information available for review. Any forensic psychiatric opinion should be understood only in the context of the specific evaluation in which it is offered. Legal questions should be addressed by qualified counsel.