Unsoundness of Mind as General Exception: Section 22 BNS and the McNaughton Rules

A person who does not know what he is doing, or does not know that what he is doing is wrong, cannot be treated as a criminal. This intuition, expressed in Roman law and formalised by the English common law in McNaughton's case (1843), is at the heart of Section 22 of the Bharatiya Nyaya Sanhita, 2023 (formerly Section 84 IPC). The section codifies the defence of unsoundness of mind and marks the boundary between the criminal law and the mental health regime. This module walks through the section, the McNaughton Rules, the distinction between legal and medical insanity, and the leading Indian authorities.

1. Meaning and Concept

Unsoundness of mind in criminal law

Unsoundness of mind, in the criminal law sense, is not the same as unsoundness of mind in the medical or psychiatric sense. The criminal law is interested in a narrow question: was the accused, at the moment of the act, incapable of understanding either what he was doing or that it was wrong. That inquiry may or may not correspond to any recognised psychiatric diagnosis. A person with a diagnosed mental illness may still have known what he was doing and that it was wrong, in which case Section 22 does not help him. A person without any formal diagnosis may, in a specific episode of confusion or delusion, have satisfied the section's requirements.

Legal insanity and medical insanity distinguished

Legal Insanity	Medical Insanity
A concept of the criminal law.	A concept of psychiatry and clinical medicine.
The narrow question: did the accused, at the time of the act, know its nature or its wrongness?	The broad question: does the person have a diagnosed mental disorder?
Focus on the moment of the act.	Focus on the person as a whole.
A defence only in specified circumstances.	A medical condition requiring treatment, whatever its legal significance.
Assessed by the court on the evidence.	Assessed by a psychiatrist through clinical examination.

Rationale of the exception

Absence of mens rea. A person who does not know what he is doing, or that it is wrong, cannot form the guilty mind that criminal responsibility requires.
Absence of deterrent effect. A person acting under a mental derangement cannot be deterred by criminal punishment, so the classical deterrent theory of punishment has no application.
Better addressed by treatment. The state's response should be medical and therapeutic rather than penal. Section 367 BNSS (formerly Section 328 CrPC) prescribes the procedure for judicial commitment to a mental health institution.

2. Historical Origin

Roman and canon law

Roman law recognised the defence of insanity from an early date. A person furiosus (insane) or mente captus (mentally captured) could not be held criminally responsible for acts committed during the derangement. The canon law of the medieval church absorbed the Roman rule and connected it to the moral requirement of a rational, choosing agent. St Thomas Aquinas, in the Summa Theologiae, treated insanity as removing the capacity for moral responsibility.

English common law before McNaughton

English common law recognised the defence of insanity from at least the thirteenth century. Bracton, writing in the 1250s, treated it as excluding criminal responsibility. Coke and Hale developed the doctrine. But the tests were varied and imprecise, ranging from complete idiocy (wild beast test) to good and evil knowledge tests. Judicial application varied from case to case.

McNaughton's case (1843)

📖 R. v. McNaughton, (1843) 10 Cl & Fin 200

Daniel McNaughton, a Scottish woodturner, believed that the Tory government was persecuting him. He travelled to London intending to kill Prime Minister Sir Robert Peel. He mistook Edward Drummond, Peel's private secretary, for Peel and shot him dead. He was acquitted on grounds of insanity.

The verdict caused public outrage, and the House of Lords put five questions to the judges of England. The judges' answers, delivered by Chief Justice Tindal, became known as the McNaughton Rules and have governed the English law of insanity ever since.

The core McNaughton test: to establish a defence on the ground of insanity, it must be clearly proved that, at the time of the committing of 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.

Reception into the Indian Penal Code

Macaulay, drafting the IPC in the 1830s, was a contemporary of the McNaughton case, though the code was completed before the case was decided. Section 84 IPC codifies a version of the test that would become the McNaughton Rules. The Bharatiya Nyaya Sanhita retains the section, unchanged in substance, as Section 22. The Indian version differs from McNaughton in one detail: it requires either incapacity to know the nature of the act, or incapacity to know that it is wrong OR contrary to law. This alternative (wrong or contrary to law) makes the Indian test marginally more accommodating than the English one.

3. Statutory Provision

Section 22 BNS (formerly Section 84 IPC)

Section 22 BNS

Nothing is an offence which is done by a person who, at the time of doing it, by reason of unsoundness of mind, is incapable of knowing the nature of the act, or that he is doing what is either wrong or contrary to law.

Text and structural analysis

The section has four elements. All must be established for the exception to succeed.

There must be unsoundness of mind.
It must exist at the time of the act.
It must render the accused incapable of knowing either (a) the nature of the act OR (b) that the act is wrong or contrary to law.
The alternative test in the third element means that either kind of incapacity is enough. The accused need not show both.

4. Ingredients of Section 22

Unsoundness of mind

The phrase is left undefined by the Sanhita. Judicial interpretation has established that it covers a wide range of mental derangements: schizophrenia, psychosis, severe depression, delusional disorders, dementia, idiocy, senile decay, epileptic fits, and similar conditions where the mind is not functioning normally. Temporary derangements caused by involuntary intoxication or by severe illness with delirium can also qualify, though voluntary intoxication is treated separately under Sections 23 and 24 BNS.

At the time of doing the act

The section requires the unsoundness of mind to be present at the moment of the act. Evidence of prior mental illness, or of subsequent institutionalisation, is not sufficient. The court must be satisfied that the derangement was operative at the specific time. This is often established through conduct immediately before and after the act, and through the accused's own account and demeanour.

Incapable of knowing the nature of the act

This limb captures cases where the accused, because of his mental state, did not understand what he was physically doing. The classical illustration is the delusional belief that the person being attacked is a wild animal or an inanimate object. Chirangi v. State of Nagpur, discussed under mistake of fact, is an example: the father, in a fever-induced delusion, believed his son was a tiger.

Incapable of knowing the act is wrong or contrary to law

This limb captures cases where the accused knew what he was doing physically, but did not know it was wrong. The wrong here means morally wrong or legally wrong. This limb is often relied upon in cases of delusional belief that the act was commanded by God, or was necessary to protect against an imagined threat. The Indian version, by adding contrary to law as an alternative to wrong, is marginally more accommodating than the English McNaughton test.

5. Legal vs Medical Insanity

Every case of medical insanity is not legal insanity

The distinction is central to the operation of Section 22 BNS. A person may have a serious diagnosed mental illness and yet, at the moment of the act, be aware of what he was doing and that it was wrong. In such a case, the medical evidence does not translate into a legal defence. Conversely, in rare cases, a person without any prior psychiatric history may, during a brief episode of derangement, satisfy the section.

📖 Surendra Mishra v. State of Jharkhand, (2011) 11 SCC 495

The Supreme Court reiterated that only legal insanity, not medical insanity, is a defence under Section 84 IPC. The accused must show that his cognitive faculties were so impaired at the time of the act that he did not know what he was doing or that it was wrong. Every mental illness, however serious, does not automatically satisfy the section.

The narrow test the law applies

The test is cognitive. The section asks about knowing, not about willing, feeling or self control. A person who knew what he was doing and knew it was wrong is not protected by Section 22, even if he could not control the impulse to do it. This is the classical criticism of the McNaughton Rules: they exclude irresistible impulse as a defence. Indian law follows the classical position and has not adopted diminished responsibility (recognised in English law under the Homicide Act, 1957) as a general defence.

Types of insanity commonly recognised

Idiocy. Congenital absence of intellectual development.
Dementia. Progressive cognitive decline, usually associated with old age or degenerative disease.
Mania and psychosis. Severe mental disorder with loss of contact with reality.
Melancholia and severe depression. Profound depressive states with suicidal or homicidal ideation.
Delusional disorders. Fixed false beliefs held with unshakeable conviction.
Schizophrenia. Chronic psychotic disorder with hallucinations, delusions, and disorganised thinking.
Somnambulism. Actions performed while sleepwalking, in some cases treated as involuntary and outside the reach of the criminal law altogether.
Epileptic derangement. Acts committed during or immediately after an epileptic fit.

6. Judicial Elaboration

Ashiruddin Ahmed v. King

📖 Ashiruddin Ahmed v. King, AIR 1949 Cal 182

The accused, believing that a divine command had directed him to sacrifice his son, killed the child. The Calcutta High Court held that the accused was entitled to the benefit of Section 84 IPC. He knew the nature of the act (killing his son) but he did not know it was wrong, because he believed it was commanded by God. Rule: a delusion that the act is commanded by divine authority may satisfy the second limb of the section (incapacity to know the act is wrong).

Bapu v. State of Rajasthan

📖 Bapu v. State of Rajasthan, (2007) 8 SCC 66

The Supreme Court considered the plea of insanity where the accused had killed his brother. The Court set out the following principles: (i) every mental illness is not necessarily insanity within Section 84 IPC; (ii) the crucial question is the state of mind of the accused at the time of the offence; (iii) the burden is on the accused to prove insanity on a preponderance of probabilities; and (iv) the accused's conduct before, during and after the offence is relevant evidence.

Dahyabhai Chhaganbhai Thakkar v. State of Gujarat

📖 Dahyabhai Chhaganbhai Thakkar v. State of Gujarat, AIR 1964 SC 1563

The accused pleaded insanity to a charge of murder. The Supreme Court laid down the classical Indian rule on the burden of proof. Although the burden of establishing insanity rests on the accused under Section 105 IEA (now Section 108 BSA), this burden is discharged on a preponderance of probabilities. Even where the accused fails to establish the defence on the balance of probabilities, if his evidence creates a reasonable doubt on any ingredient of the offence (particularly mens rea), he is entitled to acquittal. Rule: the insanity defence and the presumption of innocence operate together.

Ratan Lal v. State of Madhya Pradesh

📖 Ratan Lal v. State of Madhya Pradesh, (1970) 3 SCC 533

The accused set fire to his neighbour's haystack. There was medical evidence of previous mental illness and admission to a mental hospital. The Supreme Court held that the crucial question is not whether the accused had a history of mental illness, but whether he was capable of knowing the nature or wrongness of his act at the time of committing it. On the facts, the Court found that the accused's conduct at the time did not suggest incapacity, and the defence failed. Rule: the temporal focus is at the time of the act, not general history.

Surendra Mishra v. State of Jharkhand

Discussed above. Reiteration of the distinction between legal and medical insanity. Only legal insanity, judged by the cognitive test of Section 84 IPC (now Section 22 BNS), is a defence.

Hari Singh Gond v. State of Madhya Pradesh

📖 Hari Singh Gond v. State of Madhya Pradesh, (2008) 16 SCC 109

The Supreme Court reiterated that the plea of insanity is to be examined with reference to the accused's conduct at the time of the offence. Medical evidence of prior treatment is relevant but not decisive. The accused's actions immediately before, during and after the offence, and any evidence of concealment or awareness of consequences, must be considered.

7. Burden of Proof and Standard of Proof

Section 108 of the Bharatiya Sakshya Adhiniyam, 2023 (formerly Section 105 IEA), places the burden of proving unsoundness of mind on the accused. The standard he must meet is preponderance of probabilities, not proof beyond reasonable doubt. This is the classical Indian rule.

Even where the accused fails to establish the defence on the balance of probabilities, the Dahyabhai principle preserves the presumption of innocence. If the evidence of unsoundness of mind, though not enough to establish the defence, creates a reasonable doubt on mens rea, the accused is entitled to acquittal on the ground that the prosecution has not proved the mental element beyond reasonable doubt.

The two step Dahyabhai analysis

Step one. Has the accused established the defence of unsoundness of mind on a preponderance of probabilities? If yes, acquittal on the ground of insanity.
Step two. If no, does the evidence still create a reasonable doubt on mens rea? If yes, acquittal on the ground that the prosecution has not proved its case.

8. Distinction from Diminished Responsibility

English law, since the Homicide Act, 1957, recognises a partial defence of diminished responsibility for murder. Where the accused was suffering from an abnormality of the mind that substantially impaired his mental responsibility, murder is reduced to manslaughter. Indian law does not recognise diminished responsibility as a general defence. The choice is between full acquittal under Section 22 BNS and full conviction. Repeated Law Commission recommendations to introduce a partial defence have not been acted upon.

9. Procedure Where the Accused is of Unsound Mind

The Bharatiya Nagarik Suraksha Sanhita, 2023, provides a distinct procedure for accused persons who are of unsound mind.

Section 367 BNSS (formerly Section 328 CrPC): where the magistrate at the inquiry, or the court at the trial, has reason to believe that the accused is of unsound mind and consequently incapable of making his defence, the inquiry or trial must be postponed. A medical examination is directed.
Section 368 BNSS (formerly Section 329 CrPC): similar procedure at the trial stage.
Section 374 BNSS: where the accused is acquitted on the ground of unsoundness of mind, the court orders that he be detained in safe custody in a place and manner it thinks fit.
Section 376 BNSS: the state government may direct the removal of the accused from custody to a mental health establishment for treatment. The Mental Healthcare Act, 2017, applies to the treatment regime.

10. Consolidated Landmark Judgments

R. v. McNaughton, (1843) 10 Cl & Fin 200. The McNaughton Rules. Foundational English case.
Ashiruddin Ahmed v. King, AIR 1949 Cal 182. Delusion of divine command as a defence.
Dahyabhai Chhaganbhai Thakkar v. State of Gujarat, AIR 1964 SC 1563. Burden and standard of proof. Two step analysis.
Ratan Lal v. State of Madhya Pradesh, (1970) 3 SCC 533. Temporal focus at the time of the offence, not prior history.
Sheralli Wali Mohammed v. State of Maharashtra, (1972) 4 SCC 79. The plea of insanity requires proof of the accused's state of mind at the time of the offence.
Bapu v. State of Rajasthan, (2007) 8 SCC 66. Detailed statement of the principles governing the insanity defence.
Hari Singh Gond v. State of Madhya Pradesh, (2008) 16 SCC 109. Conduct immediately before, during and after the offence is relevant.
Surendra Mishra v. State of Jharkhand, (2011) 11 SCC 495. Distinction between legal and medical insanity.
Anandrao Bhosale v. State of Maharashtra, (2002) 7 SCC 748. Reaffirmation of the Dahyabhai principle.
Sudhakaran v. State of Kerala, (2010) 10 SCC 582. Evaluation of medical evidence on insanity.

Frequently Asked Questions

What is Section 22 BNS?

What are the McNaughton Rules?

The McNaughton Rules are the classical English test of criminal insanity, laid down in R v McNaughton (1843). The core test requires that the accused, at the time of the act, was labouring under such a defect of reason, from disease of the mind, as not to know the nature and quality of the act, or, if he did know it, that he did not know he was doing what was wrong.

What is the difference between legal and medical insanity?

Legal insanity is a defence in criminal law, judged by the narrow cognitive test of Section 22 BNS: was the accused, at the moment of the act, incapable of knowing its nature or wrongness. Medical insanity is a psychiatric or medical concept covering any diagnosed mental disorder. Every case of medical insanity is not legal insanity. Surendra Mishra v State of Jharkhand (2011) is the leading authority.

Who bears the burden of proving insanity?

Section 108 of the Bharatiya Sakshya Adhiniyam, 2023, places the burden on the accused. He must prove the defence on a preponderance of probabilities, not beyond reasonable doubt. Even where he fails on this standard, if his evidence creates a reasonable doubt on mens rea, he is entitled to acquittal (Dahyabhai principle).

Is irresistible impulse a defence in India?

No. Section 22 BNS follows the McNaughton cognitive test: it asks about knowing, not about willing or self control. A person who knew what he was doing and knew it was wrong is not protected, even if he could not control the impulse to do it. India has not adopted diminished responsibility as a general defence, unlike English law under the Homicide Act, 1957.

What happens to an accused acquitted on grounds of insanity?

Section 374 BNSS (formerly Section 335 CrPC) empowers the court to order safe custody of the accused. Section 375 BNSS provides for removal to a mental health establishment for treatment. The Mental Healthcare Act, 2017, governs the treatment regime. The accused is not simply set free.

Unsoundness of Mind Section 22 BNS