M'Naghten's case

Daniel M'Naghten was a Scottish woodturner who, in January 1843, shot and killed Edward Drummond, the private secretary to Sir Robert Peel, the then Prime Minister. M'Naghten had apparently mistaken Drummond for Peel himself. At the time of the killing, M'Naghten was suffering from a severe paranoid delusion, believing that he was being persecuted by the Tory party and by Peel in particular. Evidence adduced at trial established that his mental state had been markedly disordered for some considerable period prior to the act.

M'Naghten was tried for murder at the Central Criminal Court. Medical witnesses testified that he was labouring under a delusion of persecution at the time of the act, such that he did not appreciate the moral character of what he was doing. The jury, directed by Tindal CJ, returned a verdict of not guilty by reason of insanity. M'Naghten was accordingly ordered to be detained at the pleasure of the Crown, and was committed to Bethlem Royal Hospital, later transferring to Broadmoor.

The acquittal provoked considerable public controversy, including concern expressed by Queen Victoria herself, who had on previous occasions been the subject of attempts on her life by persons subsequently found not guilty on grounds of insanity. The House of Lords took the unusual step of summoning the judges — the fifteen common law judges of England — to answer a series of abstract questions of law concerning the doctrine of insanity as a defence to criminal charges. This procedure, now obsolete, permitted the Lords to obtain authoritative judicial opinions on questions of law without an appeal in the conventional sense being before them.

Five questions were put to the judges. The answers given by Tindal CJ, on behalf of himself and all but one of the judges present, constitute the M'Naghten Rules. These rules have since provided the foundational common law test for the insanity defence in England and Wales, and have exerted profound influence across common law jurisdictions worldwide. The answers were delivered in 1843 and are reported at (1843) 10 Cl & F 200; [1843] UKHL J16.

It should be noted that M'Naghten's case does not, in the strict technical sense, constitute a reported judgment on appeal. Rather, it records the advisory opinions of the judges of England in response to questions posed by the peers. Its authority, however, has never seriously been doubted, and it has been consistently applied and affirmed as stating the law of insanity by courts at the highest level for over 180 years.

The central question posed to the judges was: what is the proper legal test to determine whether a person accused of a crime is relieved of criminal responsibility by reason of insanity? More specifically, the peers asked the judges to articulate the directions that ought to be given to a jury where a defence of insanity is raised, having regard to the state and degree of mental disorder required to excuse criminal conduct.

A further discrete question concerned the position of a defendant who acts under a partial delusion — that is, a person who knows the nature and quality of the act and knows that it is wrong in general terms, but who labours under a specific delusional belief about the circumstances. The peers wished to know whether such a person could avail themselves of the insanity defence, and if so, on what basis.

A third line of inquiry concerned the significance of medical evidence in trials of this kind: specifically, whether medical witnesses could give opinions on the question of insanity based solely upon facts read to them in court without having personally examined the accused. This procedural question, though of lesser doctrinal importance, formed part of the overall inquiry.

Tindal CJ, delivering the answers on behalf of the judges, begins from the presumption of sanity. Every person is presumed to be sane and to possess sufficient reason to be responsible for their crimes, until the contrary is proved to the satisfaction of the jury. This presumption places the burden of establishing insanity upon the accused. The standard required is proof on the balance of probabilities, though this was not explicitly articulated in these terms in 1843; subsequent authority, notably R v Woolmington [1935] AC 462, and later cases have confirmed the position.

Having stated the presumption of sanity, Tindal CJ proceeds to define the core test. To establish a defence of insanity, it must be clearly proved that, at the time of committing the act, the party accused was labouring under such a defect of reason, from disease of the mind, as not to know the nature and quality of the act he was doing; or, if he did know it, that he did not know that what he was doing was wrong. This formulation — the M'Naghten Rules — identifies three distinct elements: a defect of reason; arising from disease of the mind; and either an inability to know the nature and quality of the act, or an inability to know that the act was wrong.

The phrase "defect of reason" is understood to denote not merely an impairment of the powers of reasoning, but a complete deprivation of the capacity to reason at the relevant time. Later authorities have confirmed that a mere failure to exercise the capacity for reason — as distinct from a total incapacity — does not satisfy this limb. In R v Clarke [1972] 1 All ER 219, the Court of Appeal held that absent-mindedness or confusion falling short of a true defect of reason does not engage the insanity defence.

The requirement that the defect of reason must arise from "disease of the mind" has generated the most substantial body of subsequent jurisprudence. Tindal CJ does not define the phrase with precision, but its meaning has been substantially elaborated by the courts. The House of Lords in R v Sullivan [1984] AC 156 confirmed that "disease of the mind" is a legal, not a medical, concept. It encompasses any mental disorder which has manifested itself in violence and is prone to recur. In that case, epilepsy was held capable of constituting a disease of the mind for these purposes. Similarly, in R v Kemp [1957] 1 QB 399, arteriosclerosis causing a temporary interruption of the blood supply to the brain was held to be a disease of the mind, even though the condition was physical in origin.

The distinction between "disease of the mind" within the M'Naghten Rules (giving rise to a verdict of not guilty by reason of insanity) and automatism not arising from a disease of the mind (giving rise to a simple acquittal) became of critical practical importance given the different consequences of each verdict. In R v Quick [1973] QB 910, the Court of Appeal distinguished between internal causes of mental malfunction — which engage the insanity defence — and external causes — which may ground a plea of non-insane automatism. A hypoglycaemic episode induced by an insulin injection was held to arise from an external cause and thus fell outside the M'Naghten framework. This internal/external distinction remains the primary tool for determining whether a condition amounts to a disease of the mind.

Turning to the first cognitive limb — not knowing the nature and quality of the act — the judges' answers indicate that this refers to a situation in which the defendant does not appreciate what he is physically doing. The classic illustration is of a defendant who, whilst cutting a woman's throat, believes he is cutting a loaf of bread. The defendant must be entirely unaware of the physical character of his conduct. This is a narrow criterion, and many defendants whose mental illness is severe will in fact be aware of the physical nature of their actions even if profoundly disordered.

The second cognitive limb — not knowing that the act was wrong — has been interpreted to mean not knowing that the act was legally wrong, rather than merely wrong according to some personal or moral code. This was confirmed in England and Wales in R v Windle [1952] 2 QB 826, where the Court of Criminal Appeal held that "wrong" in the M'Naghten formula means contrary to law. A defendant who knew that his act was legally prohibited could not rely on the insanity defence, even if he believed the act to be morally justified in the circumstances. This restrictive interpretation has attracted academic criticism and has not been universally adopted across Commonwealth jurisdictions.

On the question of partial delusion, the judges' answers provide specific guidance. Where a person is afflicted with an insane delusion and commits an offence in consequence, his responsibility must be judged by the facts as he believed them to be. If the defendant under the delusion commits an act which, had the imagined facts been true, would have amounted to a criminal offence, he will not be excused. Conversely, if the defendant, under the delusional belief, acts in circumstances which, if real, would have afforded him a complete defence (for example, killing in self-defence), he is entitled to be acquitted. This analysis treats the delusional assumption as a kind of hypothetical fact-set against which the legality of the conduct is then assessed.

The judges also address the question of medical evidence. They confirm that medical witnesses may lawfully be asked their opinion on the question of the prisoner's state of mind at the time of the act, on the assumption of the facts proved in evidence or stated in a hypothetical question. This confirms that expert opinion evidence on insanity is admissible and that a medical witness need not necessarily have personally examined the accused in order to express a view, provided that the factual basis for the opinion is properly established. This aspect of the answers is of less doctrinal significance today given modern rules on expert evidence.

A notable feature of the rules, much criticised by later commentators, is that they are entirely cognitive in character. The test asks only whether the defendant knew the nature and quality of the act, or knew it to be wrong. It does not address the defendant's volitional capacity — that is, whether, even if knowing the act to be wrong, he was able to refrain from doing it. Proposals to introduce a volitional limb into English law — mirroring the approach in some American jurisdictions and the Scottish common law — have been repeatedly considered and repeatedly declined. The Law Commission, in its report Criminal Liability: Insanity and Automatism (2013), proposed reform but no legislative change has followed.

The judges acknowledge in passing that their answers were given reluctantly and under unusual circumstances, the process of putting abstract questions being somewhat irregular. Nevertheless, the answers are deliberately expressed in general terms, as statements of principle applicable to all future cases, rather than as answers confined to the particular facts of M'Naghten's own case. The generality and authority of the formulation are the principal reasons why it has endured as the foundational statement of the law.

The M'Naghten Rules, as stated by Tindal CJ, hold that the proper direction to a jury on a defence of insanity is as follows: every man is to be presumed to be sane and responsible for his crimes; to establish a defence on the ground of insanity, it must be clearly proved that at the time of committing the act the party accused was labouring under such a defect of reason, from disease of the mind, as not to know the nature and quality of the act he was doing; or, if he did know it, that he did not know he was doing what was wrong.

In the case of partial delusion, the defendant is to be treated as if the facts were as he believed them to be, and his criminal responsibility is assessed accordingly. The test remains cognitive: the law is concerned with the defendant's knowledge, and not with his capacity for volitional control.

A successful plea of insanity at common law results in a verdict of not guilty by reason of insanity — historically known as a special verdict — and does not result in an unqualified acquittal. The disposal consequences of such a verdict have varied across time and have been substantially modified by statute, most recently by the Criminal Procedure (Insanity and Unfitness to Plead) Act 1991 and the Domestic Violence, Crime and Victims Act 2004, which expanded the range of disposals available to the court.

M'Naghten's case is the single most important authority in the English law of criminal insanity. The rules formulated by the judges in 1843 remain the operative common law test in England and Wales to the present day, and have been applied in thousands of subsequent cases across more than 180 years. They have been adopted, with varying degrees of modification, in Australia, Canada, New Zealand, India, and many other common law jurisdictions. In the United States, the M'Naghten test formed the predominant standard for insanity in most states until the latter half of the twentieth century, when alternative formulations gained ground following the Model Penal Code.

The rules have been the subject of sustained academic and law reform criticism, principally on three grounds. First, the purely cognitive nature of the test is said to fail to capture the full range of serious mental disorder; a defendant may know that an act is wrong and yet be totally unable, by reason of mental illness, to conform his conduct to that knowledge. Second, the legal definition of "disease of the mind" has been criticised for encompassing conditions — such as epilepsy, sleepwalking, and arteriosclerosis — which the psychiatric community would not regard as mental illness, whilst potentially excluding others which plainly are. Third, the historically severe consequences of a special verdict of not