Study Notes by Akinchan Aggarwal, Advocate — B.A. (Hons.) Gold Medalist, LL.B., LL.M. (Disputes Resolution), UGC–NET, Ph.D. (pursuing)
A man can be diagnosed with a serious mental illness. He can have been hospitalised for it, medicated for it, certified for it. Psychiatrists can agree, unanimously, that he is ill.
And he can still be convicted of murder and hanged.
That is not a flaw in Indian criminal law. It is the deliberate design of Section 22 of the Bharatiya Nyaya Sanhita, 2023 — because the defence it creates is legal insanity, and legal insanity is not medical insanity. The two overlap, but they are not the same enquiry, they are not proved by the same evidence, and a great many people who are genuinely unwell fall outside the section entirely.
The BNS position: Section 22 reproduces s 84 of the Indian Penal Code, 1860 word for word. The Sanhita did not modernise the language, did not adopt "mental illness" in place of "unsoundness of mind", and did not import diminished responsibility. A rule framed by the House of Lords in 1843 continues to govern the insanity defence in India, unchanged, in 2026.
Contents
- The Section Map
- Section 22 — The Bare Text
- The M'Naghten Case and the Rules
- The Three Ingredients
- Legal Insanity Is Not Medical Insanity
- "Nature of the Act" — What It Means
- "Wrong" or "Contrary to Law" — Why Both Words
- What Does Not Qualify
- What Can Qualify
- Only at the Moment of the Offence
- Burden of Proof — The Four Propositions
- The Investigating Officer's Duty
- Trial of a Person of Unsound Mind
- Reform That Never Came
- Points to Remember
- Frequently Asked Questions
1. The Section Map
| Provision | IPC, 1860 | BNS, 2023 |
|---|---|---|
| Act of a person of unsound mind | s 84 | s 22 |
| Act of a person incapable of judgment by reason of intoxication caused against his will | s 85 | s 23 |
| Offence requiring particular intent or knowledge, committed by one who is intoxicated | s 86 | s 24 |
| Private defence against the act of a person of unsound mind | s 98 | s 36 |
All of these sit in Chapter III of the BNS — the General Exceptions. A successful plea produces an acquittal, not a reduced conviction.
2. Section 22 — The Bare Text
Section 22, BNS, 2023 (formerly s 84, IPC) — Act of a person of unsound mind:
"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."
Note at once what the section does not say. It does not use the word "insanity". It does not define "unsoundness of mind" — the expression is undefined in the Code and in the Sanhita alike. And it asks nothing about diagnosis, treatment or illness. It asks only about capacity to know, and only at one instant in time.
3. The M'Naghten Case and the Rules
The foundation was laid by the House of Lords in 1843.
Daniel M'Naghten suffered from a delusion that Sir Robert Peel, then Prime Minister of Britain, had injured him. He mistook Edward Drummond, Secretary to the Prime Minister, for Peel, and shot and killed him. Medical evidence showed M'Naghten was labouring under a morbid delusion that carried him beyond the power of his own control. The jury found him "not guilty by reason of insanity". He was detained in a mental hospital.
The acquittal caused public excitement and considerable furore. The verdict became the subject of debate in the House of Lords, and to settle the law, five questions were formulated and put to the Lords for definite answers. Those answers are the M'Naghten Rules. The second and third questions and their answers form the core of the law.
The three principles
- Every person is presumed to be sane, and to possess a sufficient degree of reason to be responsible for his crimes, until the contrary is established.
- To establish the defence, it must be clearly proved that at the time of committing the crime the person was so insane 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.
- The test of wrongfulness lies in the power to distinguish between right and wrong not in the abstract or in general, but in regard to the particular act committed.
Section 22 more or less embodies these principles. Indian courts have treated "unsoundness of mind" as equivalent to "insanity" — both meaning a defect of reason arising from a disease of the mind.
4. The Three Ingredients
To claim the protection of s 22, the accused must prove that, by reason of unsoundness of mind, he was:
- incapable of knowing the nature of the act; or
- incapable of knowing that the act was contrary to law; or
- incapable of knowing that the act was wrong.
These are alternatives, not cumulative requirements. Establishing any one of the three suffices. And the crucial point of time for all three is the moment the offence was committed — insanity before or after is not, by itself, enough to absolve.
5. Legal Insanity Is Not Medical Insanity
This is the proposition on which nearly every insanity plea in India turns, and the one to state first in any answer.
Not every person suffering from mental disease is ipso facto exempt from criminal liability. The following have all been held insufficient to attract the section:
- That the accused was conceited, odd, irascible, or that his brain "is not quite alright";
- That physical and mental ailments had rendered his intellect weak or affected his emotions;
- That he indulged in certain unusual acts;
- That he had fits of insanity at short intervals;
- That he was subject to epileptic fits with abnormal behaviour;
- That his behaviour was queer.
As the courts have put it, a mere warped or twisted mind, which many a criminal has, cannot qualify as an "unsound mind".
The test
It is not every type of insanity recognised medically that receives the protection of this section. The insanity must be of such a nature that it completely impairs the cognitive faculty of the mind, to such an extent that the accused is incapable of knowing the nature of his act, or that what he is doing is wrong or contrary to law.
It is only legal, and not medical, insanity that absolves an accused from criminal responsibility.
This is why a psychiatric diagnosis, standing alone, wins nothing. The question a court asks is not "was he ill?" but "was his cognitive faculty so impaired that, at that instant, he could not know what he was doing or that it was wrong?"
6. "Nature of the Act" — What It Means
A person is incapable of knowing the nature of the act if, at the time of doing it, he was ignorant of the physical characters of the act.
Sir James Stephen's illustration is the one every student should carry, because nothing explains the concept faster. An idiot cut off the head of a man he found sleeping — because, as he explained, it would be such fun to watch him looking about for his head when he awoke. It is quite certain he had no idea that his fun would be lost, because the man would never wake.
That is ignorance of the nature of the act. The man did not misjudge the morality of decapitation; he did not understand what decapitation is.
Conversely: if at the time of committing the offence the accused knew the nature of the act, he is obviously punishable — unless he brings himself within one of the other two limbs.
7. "Wrong" or "Contrary to Law" — Why Both Words
A person who does an act and, by reason of insanity, does not know that the act is either wrong or contrary to law, is protected — even though he knew the nature of the act.
Now the interpretive point that examiners love. The word "wrong" is interpreted to mean a moral wrong, and not a legal wrong. The reasoning is elegant and worth reproducing:
The section uses the alternative phrase "wrong or contrary to law". The very fact that the authors used both expressions indicates that "wrong" does not mean "contrary to law" — because if it did, the already existing phrase "contrary to law" would become redundant, and the legislature would never use a word that is redundant.
So the section covers two distinct failures of moral and legal appreciation: the accused who cannot tell that what he is doing is morally wrong, and the accused who cannot tell that it is illegal.
8. What Does Not Qualify
This is where most pleas fail, and where a practitioner earns his fee by advising a client honestly at the outset.
| Condition or fact | Position |
|---|---|
| Hallucination or delusion | A person who is not insane but merely suffering from some kind of obsession or hallucination cannot invoke the section. Delusion is a state where a person may be perfectly sane as to everything but under a delusion as to one particular idea. |
| Irresistible impulse | Never accepted as a defence, unless it is attributable to unsoundness of mind. Impulsive insanity likewise. Irresistible impulse indicates loss of control, not unsoundness of mind. |
| Mental agitation, annoyance, fury | All indicate loss of control, not unsoundness of mind. Every minor mental aberration is not insanity. |
| Uncommon ferocity, moderate depression, over-sensitiveness | Do not necessarily lead to an inference that mental capacity was affected. |
| Extreme anger | An act committed because of extreme anger — and not as a consequence of unsoundness of mind — does not bring its doer within the section. |
| Strange behaviour after the offence | Mere strange behaviour exhibited after commission does not necessarily indicate lack of the requisite mens rea. |
| Absence of motive | The absence of a strong and adequate motive for a serious offence is not by itself proof of insanity. It may, however, be considered along with other circumstances. |
| A trifling reason | Causing death over a trifling matter does not by itself warrant a conclusion of insanity. A crime committed for a paltry reason is no defence. |
| Brutality of the act | Brutality and ferociousness cannot by themselves lead to a conclusion of insanity. In the memorable formulation: "a crime cannot be excused by its own atrocity." One must look beyond the act itself for evidence of how far the accused acted with knowledge. |
| Mere probability | Circumstances indicating a mere probability of legal insanity are not sufficient to discharge the accused's onus. |
9. What Can Qualify
Somnambulism
Sleepwalking — the unconscious state known as walking in sleep — if proved, constitutes unsoundness of mind, and the accused gets the benefit of the section.
Fits of insanity and lucid intervals
The section applies even in cases of fits of insanity with lucid intervals. But in such cases it must be proved that at the time of commission the accused was suffering from a fit which rendered him incapable of knowing the nature of his act — and that the act was not committed during a lucid interval.
Insanity produced by drink or ganja
Where insanity is caused by excessive drinking — even involuntary — or by smoking ganja or other drugs, that insanity will amount to unsoundness of mind, if it makes the person incapable of understanding what he is doing or that it is wrong or illegal. The accused may take shelter under the section if he proves the insanity existed at the time of the act.
But note the line carefully. A mere loss of self-control due to excessive drinking, smoking ganja, or abuse of cannabis and alcohol does not entitle a person to this immunity. The distinction is between intoxication that produces a disease of the mind and intoxication that merely disinhibits. Only the first engages s 22; the second is governed by ss 23 and 24.
The two classical categories
Law groups insanity under two broad heads:
- Dementia naturalis — individuals insane from birth; and
- Dementia adventitia (or accidentialis) — individuals who become insane after birth.
There are, however, no hard and fast rules about which kinds of insanity courts will recognise as legal insanity. A survey of the case law shows that courts are influenced more by the facts of the case and the nature of the crime than by any formal evidence as to the kind of insanity involved.
10. Only at the Moment of the Offence
The law is concerned only with insanity existing at the time of committing the offence. Unsoundness of mind before or after is neither relevant nor per se sufficient — though it may be taken into consideration in deciding whether the accused was insane at the material moment.
| Case | Facts and holding |
|---|---|
| State of Madhya Pradesh v Ahmadulla | The accused murdered his mother-in-law, towards whom he bore ill-will in connection with his divorce. He did it at night, having scaled a wall to get into the house, with the aid of a torch, entering the room where she slept. The Supreme Court held this showed a crime committed not in a sudden mood of insanity but preceded by careful planning and cool calculation, and directed against a person he considered his enemy. Setting aside the acquittals of both the sessions court and the High Court, it convicted him of murder. |
| Bhikari v State of Uttar Pradesh | The accused had, a few months earlier, threatened to kill all the family members of the deceased. On the day of the event, though other people were present, he carefully chose only the children of that family. Held: his actions were deliberate and premeditated, not the acts of an insane man. |
The pattern in both is the same, and it is the single most useful thing a practitioner can take from this chapter: evidence of planning, selection and concealment destroys the plea. Scaling a wall, carrying a torch, choosing a target, waiting for night — each of these is proof of a mind that knew exactly what it was doing.
11. Burden of Proof — The Four Propositions
When insanity is pleaded, it is not the duty of the prosecution to establish affirmatively that the accused was capable of knowing the nature of his act. Every person is presumed to know the law and the natural consequences of his acts. The prosecution has merely to prove the basic facts and rely on those presumptions. It is then for the accused to rebut them.
The Supreme Court has outlined the position in four propositions:
- The prosecution must prove beyond reasonable doubt that the accused committed the offence with the requisite mens rea, and that burden rests on the prosecution from the beginning to the end of the trial.
- There is a rebuttable presumption that the accused was not insane. He may rebut it by placing before the court all relevant evidence — oral, documentary or circumstantial — but the burden upon him is no higher than that which rests on a party to civil proceedings.
- Even if the accused cannot establish conclusively that he was insane, the evidence placed before the court — by him or by the prosecution — may raise a reasonable doubt as regards one or more ingredients of the offence, including mens rea. In that case the court is entitled to acquit, on the ground that the general burden on the prosecution was not discharged. An accused succeeds not because he proves his case to the hilt, but because his version casts a doubt on the prosecution case.
- The standard for ascertaining unsoundness of mind is whether the accused, according to the ordinary standard adopted by a reasonable man, was able to judge whether his act was right or wrong.
In short: the accused need not prove insanity beyond reasonable doubt. He must establish the probability of its existence at the time of the offence — the civil standard, a preponderance of probabilities in his favour.
A candid note from the commentary: courts in India have, by and large, been very cautious in accepting the plea of insanity.
12. The Investigating Officer's Duty
This is the least-known proposition in the chapter and among the most useful in practice.
It becomes obligatory on the part of the investigating officer to get the accused medically examined immediately when a previous history of insanity or abnormality of mind is revealed to him, or comes or is brought to his notice — and to place that evidence before the court.
Failure to carry out the medical examination creates a serious infirmity in the prosecution case, and entitles the accused to the benefit of doubt and consequential acquittal.
For defence counsel, the practical sequence follows immediately. If there is any history of mental illness, bring it to the investigating officer's notice on the record, in writing, at the earliest. If he then fails to have the accused examined, that failure becomes a defect in the prosecution case rather than a gap in yours.
13. Trial of a Person of Unsound Mind
A special procedure governs the trial of an accused of unsound mind — historically Chapter XXV of the Code of Criminal Procedure, 1973 (ss 328–339), and now the corresponding provisions of the Bharatiya Nagarik Suraksha Sanhita, 2023. The substance:
- If during trial it appears to the judge that the accused is of unsound mind and consequently incapable of making his defence, the court must first conduct an enquiry and try the fact of such unsoundness and incapacity.
- Failure to do so vitiates the whole trial.
- If the court concludes the accused is of unsound mind, the trial is postponed until he is treated and is in a position to understand the proceedings and defend himself.
- Where the accused is acquitted on the ground that by reason of unsoundness of mind he was incapable of knowing the nature of the act, the court must order that he be detained in safe custody, or delivered to a relative or friend who gives security that he will take care of him and prevent him from causing injury to himself or others.
Distinguish the two enquiries, because students routinely conflate them. Capacity to stand trial is a question about the accused's condition now, and it postpones the trial. The defence under s 22 is a question about his condition at the moment of the offence, and it results in acquittal. A man may be perfectly fit to stand trial today and still have been legally insane on the day of the killing — and the reverse.
14. Reform That Never Came
For roughly 150 years the law of insanity in India has remained static. Neither the legislature nor the courts have brought reform, despite the indicia offered by modern medical science and psychiatry, and despite progressive statutory and judicial developments in other jurisdictions — including in England, the birthplace of the M'Naghten Rules.
The Law Commission of India admitted that "unsoundness of mind", compared with the expressions "disease of the mind" and "mental deficiency" used in the M'Naghten Rules, is "somewhat vague and imprecise" — yet saw no worth in proposing changes.
It also declined to introduce diminished responsibility into the Penal Code, apprehending the complicated medico-legal issues involved, and recalling that judicial discretion in sentencing already allows courts to take extenuating circumstances, including mental abnormality, into account.
The consequence is that mental derangement falling short of s 22 has no doctrinal home in India. It is pleaded only as an extenuating circumstance at sentencing. In England, by contrast, mental abnormality falling short of complete insanity attracts diminished responsibility under the Homicide Act 1957 — which covers, among other things, killings under irresistible impulse.
Author's note: the Bharatiya Nyaya Sanhita, 2023 was the obvious occasion to revisit this, and did not. Readers should separately note the framework of the Mental Healthcare Act, 2017, which governs the treatment and rights of persons with mental illness and is relevant to how such an accused is dealt with in practice, though it does not alter the test under s 22.
15. Points to Remember
- Legal insanity, not medical insanity. Open every answer with this. Diagnosis alone proves nothing.
- Section 22 = s 84, IPC, verbatim. The BNS changed nothing but the number.
- Three alternative limbs — nature of the act, contrary to law, or wrong. Any one suffices.
- "Wrong" means moral wrong, because "contrary to law" already covers legal wrong and the legislature does not use redundant words.
- Only at the moment of the offence. Insanity before or after is evidence, not defence.
- Complete impairment of the cognitive faculty is the standard — not partial, not intermittent, not merely diagnosed.
- Irresistible impulse is not a defence in India, unless attributable to unsoundness of mind.
- Somnambulism qualifies. Delusion and hallucination, standing alone, do not.
- Insanity caused by drink or ganja qualifies; mere loss of self-control does not.
- Planning destroys the plea — Ahmadulla (wall, torch, night) and Bhikari (prior threats, selective targeting).
- "A crime cannot be excused by its own atrocity." Brutality is not evidence of insanity.
- Burden on the accused, at the civil standard, and he can succeed merely by raising reasonable doubt on mens rea.
- The IO must get the accused examined where a history of mental illness surfaces; failure is a serious infirmity in the prosecution case.
- Fitness to stand trial ≠ the s 22 defence. Different questions, different times, different consequences.
16. Frequently Asked Questions
Which BNS section replaced Section 84 of the IPC?
Section 22 of the Bharatiya Nyaya Sanhita, 2023, reproduced word for word. The expression "unsoundness of mind" was retained; it was not replaced with "mental illness".
What is the difference between legal insanity and medical insanity?
Medical insanity is any mental disorder recognised by medicine. Legal insanity is far narrower: unsoundness of mind that completely impairs the cognitive faculty, so that at the moment of the act the accused could not know its nature, or that it was wrong or contrary to law. Only legal insanity absolves from criminal responsibility.
What are the M'Naghten Rules?
The answers given by the House of Lords in 1843, after Daniel M'Naghten was acquitted of killing Edward Drummond. Three principles: everyone is presumed sane until the contrary is established; the defence requires clear proof that at the time of the act the accused did not know its nature and quality, or did not know it was wrong; and wrongfulness is tested in relation to the particular act, not in the abstract.
Is irresistible impulse a defence in India?
No — not unless it is attributable to unsoundness of mind. Irresistible impulse indicates loss of control, not unsoundness of mind. England recognises such cases under diminished responsibility; India has no equivalent.
Does sleepwalking count?
Yes. Somnambulism, if proved, constitutes unsoundness of mind and attracts the benefit of the section.
What if the accused was drunk or had smoked ganja?
If the drink or drug produced insanity — such that he could not understand what he was doing or that it was wrong or illegal — the section applies, provided that state existed at the time of the act. But a mere loss of self-control from excessive drinking or drug use does not attract it; intoxication is separately governed by ss 23 and 24 of the BNS.
Who has to prove insanity?
The accused — but only to the standard of a preponderance of probabilities, not beyond reasonable doubt. And he may succeed without proving it conclusively, if the evidence (including the prosecution's own) raises a reasonable doubt about mens rea.
Does a psychiatric certificate guarantee acquittal?
No. Courts have repeatedly held that odd or queer behaviour, weak intellect, epileptic fits, depression or over-sensitiveness are not enough. The question is capacity to know at the moment of the act — and Indian courts have been very cautious in accepting the plea.
What happens if the plea succeeds?
The accused is acquitted, but not simply released. The court must order that he be detained in safe custody or delivered to a relative or friend who gives security to take care of him and prevent him from causing injury to himself or others.
Does India recognise diminished responsibility?
No. The Law Commission declined to introduce it, and the BNS did not adopt it. Mental abnormality falling short of s 22 can only be urged as an extenuating circumstance in sentencing.
Conclusion
The insanity defence in India is a nineteenth-century instrument, and it was designed for a nineteenth-century question: not is this man ill? but did this man know? Everything that has happened in psychiatry since 1843 — the diagnostic manuals, the neuroimaging, the pharmacology — bears on the first question and only indirectly on the second. Section 22 asks the second, and it asks it about a single instant.
That is why the reported cases turn so often on wholly unmedical facts. A wall scaled at night. A torch carried into a bedroom. A threat made months earlier. Children selected out of a crowd. Those are not observations about a mind's health. They are observations about a mind's knowledge — and knowledge is all the section has ever measured.
Whether that remains the right test is a question the Sanhita could have reopened and chose not to. Until Parliament returns to it, the advice to a client is unchanged and unsentimental: a diagnosis is a starting point, never an answer, and the case will be decided on what your client did in the minutes before the act — not on what a doctor writes about him afterwards.
Disclaimer: These notes are prepared for educational purposes for law students, judiciary and AIBE aspirants, and practitioners, and do not constitute legal advice. Statutory provisions have been summarised and, in places, paraphrased for clarity; readers must verify the exact language against the enacted text of the Bharatiya Nyaya Sanhita, 2023 and the Indian Penal Code, 1860 before relying on it in argument or examination. The reference to the procedure for trial of persons of unsound mind is given by reference to Chapter XXV of the Code of Criminal Procedure, 1973 as stated in the standard commentary; the corresponding provisions of the Bharatiya Nagarik Suraksha Sanhita, 2023 should be checked directly. Case holdings are stated in summary form and drawn from the standard commentary; readers should consult the full reports before citation. The application of the insanity defence is intensely fact-specific and the burden of establishing it lies on the accused. This article is not a comment on any pending matter, and nothing in it should be read as medical or psychiatric guidance.
