The Defence of Insanity: Unsoundness of Mind Under the BNS

Under Section 22 of the Bharatiya Nyaya Sanhita, 2023 (BNS), nothing is an offence if the person, at the time of doing it, was by reason of unsoundness of mind incapable of knowing the nature of the act, or that it was wrong or contrary to law. This is the old Section 84 of the Indian Penal Code carried into the BNS with the same wording, so the Supreme Court's case law on Section 84 still guides courts. The test is legal insanity at the moment of the act, not a medical diagnosis on its own.

This explainer is written for B.A. LL.B. and LL.B. students preparing for criminal law papers, and for families who suddenly find that a relative with a mental illness has been arrested. Knowing how the defence works, who has to prove what, and what the court must do at the procedural stage can change the outcome of a case.

What does Section 22 of the BNS actually say?

The section reads: "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." It sits in Chapter III of the BNS (General Exceptions). The BNS came into force on 1 July 2024 and replaced the IPC. Official comparison tables published by State police departments map BNS Section 22 to IPC Section 84 with the same heading, "Act of a person of unsound mind".

Break the section into its parts when you study it:

• Unsoundness of mind must exist.
• It must exist at the time of doing the act, not only before or after.
• Because of it, the person must be incapable of knowing either (a) the nature of the act, or (b) that the act was wrong or contrary to law.

A man who knows he is striking someone with a knife, and knows it is wrong, does not get the benefit of Section 22 merely because he has a psychiatric condition.

Legal insanity or medical insanity: which one counts?

The Supreme Court has repeated many times that courts are concerned with legal insanity, not medical insanity. In Surendra Mishra v. State of Jharkhand (2011) 11 SCC 495, the Court held that eccentric or abnormal behaviour, or a mental disorder by itself, is not enough. In Prakash Nayi @ Sen v. State of Goa (judgment dated 12 January 2023), the Court said that "a mere medical insanity cannot be said to mean unsoundness of mind". Other cases relied on for this distinction are Bapu @ Gajraj Singh v. State of Rajasthan (2007) 8 SCC 66 and Hari Singh Gond v. State of M.P. (2008) 16 SCC 109.

So a diagnosis of schizophrenia is evidence, often strong evidence, but the court still asks the legal question: at that moment, could this person understand what he was doing or that it was wrong?

Who has to prove insanity, and to what standard?

Two rules work together.

1. The prosecution must always prove the offence, including the guilty mind, beyond reasonable doubt. This burden never shifts.
2. The accused who pleads insanity must bring his case within the exception. Section 108 of the Bharatiya Sakshya Adhiniyam, 2023 (formerly Section 105 of the Indian Evidence Act) places that burden on him, and its illustration (a) uses exactly this example: an accused of murder who says that, by reason of unsoundness of mind, he did not know the nature of the act.

The leading case is Dahyabhai Chhaganbhai Thakker v. State of Gujarat, AIR 1964 SC 1563. It held that there is a rebuttable presumption of sanity, and the accused's burden is no higher than that of a party to civil proceedings. Even if the accused does not fully prove insanity, the evidence may still raise a reasonable doubt about mens rea, and then he must be acquitted.

Recent judgments state the standard in plain terms. In Rupesh Manger (Thapa) v. State of Sikkim (13 September 2023) and Dashrath Patra v. State of Chhattisgarh (8 May 2025), the Supreme Court said the standard of proof to prove insanity is only a reasonable doubt. In Prakash Nayi, the Court described it as a preponderance of probabilities. In an exam, explain both phrasings and show that they point the same way: the accused does not have to prove insanity beyond reasonable doubt.

What evidence do courts look at?

Since the question is the mind at the moment of the act, courts look at behaviour before, during and after the incident. In Prakash Nayi, the Court quoted Bapu: behaviour "antecedent, attendant and subsequent to the event, may be relevant". Useful evidence includes:

• prior treatment records and prescriptions close to the date of the incident;
• statements of family members and neighbours about the accused's condition;
• conduct after the act, such as running away and hiding the weapon (which courts have read as awareness of wrongdoing) or sitting calmly at the spot with no understanding;
• a timely psychiatric examination.

Timing matters. In Dashrath Patra, the High Court relied on a medical examination done in December 2023, more than five years after the incident. The Supreme Court called it "meaningless" for judging his state at the time of the offence. It also noted that several prosecution witnesses admitted in cross-examination that the appellant's mind was unstable before and after the incident, yet the prosecution never sought a medical examination. The Court added that the right to defend a charge is a fundamental right under Article 21.

How does the BNSS handle an accused of unsound mind?

Students often mix up two different questions. Section 22 BNS asks about the mind at the time of the act. The procedure in Chapter XXVII of the Bharatiya Nagarik Suraksha Sanhita, 2023 (BNSS) also asks whether the accused is fit now to make a defence. The main provisions are:

• Section 367: procedure when an accused before a Magistrate appears to be of unsound mind, including a medical examination and referral to a psychiatrist or clinical psychologist of a Government hospital or Government medical college (old CrPC Section 328, which did not name the type of hospital).
• Section 368: the same question when the accused is tried before a court.
• Section 369: release of a person of unsound mind pending investigation or trial.
• Section 373: when a person is acquitted on the ground of unsoundness of mind, the finding must state specifically whether he committed the act or not (old CrPC Section 334).
• Section 374: a person so acquitted is to be detained in safe custody.

Read the bare text of these sections yourself before an exam, since the BNSS rewrote parts of the old chapter.

What is the position in 2026, and how should you write about it in an exam?

As of this writing, Section 22 BNS governs offences committed on or after 1 July 2024, and IPC Section 84 continues to matter for older cases still in the courts. The interpretive rules from Dahyabhai to Dashrath Patra apply to both because the wording is the same. Check India Code for any later amendment before you rely on this.

A clean answer structure for a 15 mark question:

1. Quote Section 22 BNS and give IPC Section 84 as a pointer.
2. Break it into elements and explain legal versus medical insanity, citing Surendra Mishra.
3. Explain burden under Section 108 BSA and Dahyabhai, then the reasonable doubt line in Rupesh Manger and Dashrath Patra.
4. Add the evidence point (conduct before and after, timely medical examination).
5. Close with the BNSS procedure and a short hypothetical, for example a man in Nagercoil with a long treatment history who attacks a neighbour and stays at the spot talking to himself.

Students who want to see how such cases reach real families can volunteer with the college legal aid clinic.

Sources

• India Code: Bharatiya Nyaya Sanhita, 2023: official record of Act 45 of 2023 with enforcement date 1 July 2024.
• Tripura Police: BNS and IPC comparison table: maps BNS Section 22 to IPC Section 84.
• Supreme Court of India: Prakash Nayi @ Sen v. State of Goa (2023): judgment on legal insanity, burden and the court's role.
• Supreme Court of India: Rupesh Manger (Thapa) v. State of Sikkim (2023): judgment restating Dahyabhai and the standard of proof.
• Supreme Court of India: Dashrath Patra v. State of Chhattisgarh (2025): acquittal on reasonable doubt about insanity, Article 21 point.
• AdvocateKhoj: Bharatiya Sakshya Adhiniyam, Section 108: bare text on the burden of proving a general exception.