Also known as: incapable of knowing right from wrong · M'Naghten test · right-wrong test · insanity defense
Written by attorneys · grounded in primary & secondary sources — see below
A cognitive incapacity caused by mental disease or defect that prevents recognition that conduct violates societal standards of morality. The incapacity must destroy the ability to know an act is wrong under objective community norms rather than a purely personal belief that the act is morally justified.
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Ivan Ivanov was arrested for assault and received Miranda warnings. He remained silent during questioning. At trial Ivan raised an insanity defense claiming he could not distinguish right from wrong because of schizophrenia. The prosecution attempted to introduce his post-warning silence to show he understood societal norms. The court excluded the evidence.
Isabella Ingram was charged with arson after setting fire to her workplace. Her counsel filed written notice of an insanity defense weeks after the pretrial motion deadline. The notice asserted that bipolar delusions had rendered Isabella incapable of distinguishing right from wrong. The government moved to preclude the defense for lack of timely notice. The court denied leave to file late after finding no good cause.
Irene Ingalls faced murder charges and made a preliminary showing that she would assert insanity. She requested state-funded psychiatric evaluation to prove her delusions left her incapable of distinguishing right from wrong under societal standards. The trial court denied the request. The denial prevented Irene from presenting expert evidence on her cognitive incapacity at trial.
Iain Irons shot a neighbor while suffering from fixed delusions that the neighbor was a government agent. At trial Iain introduced evidence that his mental disease left him incapable of distinguishing right from wrong. The court instructed the jury that the defense must prove the incapacity by a preponderance of the evidence. The jury rejected the defense after finding the evidence insufficient.
Isaiah Ishikawa was acquitted of sexual offenses by reason of insanity after proving his pedophilic disorder rendered him incapable of distinguishing right from wrong. The state sought civil commitment based on his ongoing dangerousness. The court ordered commitment after finding the mental abnormality continued to impair his cognitive capacity. Isaiah challenged the commitment as punitive.
Ines Ibarra was convicted of capital murder. At the penalty phase she offered psychiatric testimony that her mental disease had left her incapable of distinguishing right from wrong. The prosecution moved to exclude the evidence because the jury had already rejected an insanity defense. The court admitted the testimony solely to argue for a life sentence rather than death.
The traditional M'Naghten formulation requires that the mental disease destroy the cognitive capacity to distinguish right from wrong under societal standards. Modern jurisdictions using a substantial-capacity test lower the threshold to a significant but not total impairment.
No. The incapacity must prevent recognition that society regards the conduct as wrong. A personal moral belief that the act is justified does not satisfy the test when the defendant retains the ability to know societal standards.
…was ratified. Commonwealth v. York , 50 Mass. 93 (1845).[^maj-8] In 1895 the common-law view was abandoned with respect to the insanity defense in federal prosecutions. Davis v. United States , 160 U. S. 469 (1895). This ruling had wide impact on the practice in the federal courts with respect to the burden of proving various…
…unsoundness of mind, the unsoundness should, according to law as it has long been understood and held, be such as rendered him incapable of knowing right from wrong
…proceedings against Ake. At a pretrial conference in June, Ake’s attorney informed the court that his client would raise an insanity defense. To enable him to prepare and present such a
…43 U. Cin. L. Rev. 781 (1974). Indeed, the notion of an "irresistible impulse" often has helped to shape criminal law's insanity defense
…established by a preponderance of the evidence." D. C. Code § 24-301(j) (1981).[^maj-1] If he successfully invokes the insanity defense
The phrase addresses only the cognitive capacity to know wrongfulness. It does not encompass an inability to control conduct or conform behavior to law, which some jurisdictions treat as a separate volitional defense.
Federal Rule of Criminal Procedure 12.2 requires written notice to the government within the time for pretrial motions. Failure to provide timely notice bars reliance on the defense absent good cause for a late filing.
No. The prosecution may not introduce a defendant's post-warning silence to rebut an insanity defense because the warnings carry an implicit assurance that silence carries no penalty.