The Jurisprudence of "Insanity" in Criminal Law: Deconstructing Legal Insanity vs. Medical Insanity

Abstract The defence of insanity occupies a singular position within the General Exceptions to criminal liability, resting on the premise that the criminal law punishes only those who possessed, at the material time, the capacity to form a guilty mind. This article undertakes a doctrinal examination of the insanity defence under Indian criminal law, tracing its conceptual genesis to the M'Naghten Rules of 1843 and its statutory expression, first as Section 84 of the Indian Penal Code, 1860, and now as Section 22 of the Bharatiya Nyaya Sanhita, 2023 (BNS). The central problem addressed is the persistent conflation, in lay and sometimes in forensic discourse, of "medical insanity" a clinical diagnosis of mental illness with "legal insanity", a narrower construct confined to the accused's incapacity, at the time of the act, to know its nature or that it was wrong or contrary to law. Through an analysis of State of Madhya Pradesh v Ahmadulla, Dahyabhai Chhaganbhai Thakkar v State of Gujarat, Jai Lal v Delhi Administration, Hari Singh Gond v State of Madhya Pradesh, Surendra Mishra v State of Jharkhand, Devidas Loka Rathod v State of Maharashtra, Prakash Nayi Sen v State of Goa and Dashrath Patra v State of Chhattisgarh, the article shows how the Supreme Court has policed this boundary while progressively easing the evidentiary burden on the accused. That burden is discharged on a preponderance of probabilities under Section 105 of the Indian Evidence Act, 1872 (now Section 108 of the Bharatiya Sakshya Adhiniyam, 2023), leaving the prosecution's overarching burden of proving guilt beyond reasonable doubt undisturbed. Accused 'X' v State of Maharashtra is examined separately, as an authority on post-conviction mental illness rather than on the insanity defence itself. The analysis situates the doctrine within the rights-based framework of the Mental Healthcare Act, 2017 in particular Section 3(5), which separates a clinical determination of mental illness from a judicial finding of unsoundness of mind and the procedural provisions of Chapter XXVII (Sections 367–378) of the Bharatiya Nagarik Suraksha Sanhita, 2023. Using doctrinal legal research, the article argues that Section 22 of the BNS preserves doctrinal continuity but inadequately integrates contemporary mental health law. It concludes by proposing calibrated reforms, consideration of a partial defence of diminished responsibility, standardised forensic psychiatric evaluation, and closer coordination between criminal courts and Mental Health Review Boards while addressing the principal objections to each.