A 35-year-old man with schizophrenia commits a violent act during a florid psychotic episode, believing he was being attacked by demons. His attorney argues insanity defense. Under the McNaughton rules, what is the LEGAL standard for insanity?

• A The person had an irresistible impulse to commit the act due to mental illness
• B The person was intoxicated at the time of the act
• C The person has a documented psychiatric diagnosis at the time of the act
• D The person did not know the nature and quality of the act OR did not know it was wrong due to a disease of the mind ✓

Explanation

The McNaughton (M'Naghten) Rules (1843) established that a person is not criminally responsible if, at the time of the act, due to a disease of the mind, they either did not know the nature and quality of the act, OR knew the nature but did not know that what they were doing was wrong. This is a COGNITIVE test—it does not consider emotional or volitional capacity. The 'irresistible impulse' test (added later in some jurisdictions) considers whether the person could control their behavior even if they knew it was wrong—this was NOT part of the original McNaughton rules.

Reference: Kaplan & Sadock's Synopsis of Psychiatry, 11th ed.

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Written and medically reviewed by the StethoPrep medical team.