The M'Naghten rules (1843) define legal insanity based on which cognitive criterion?
- A The accused did not know the nature of the act, or did not know it was wrong, due to a defect of reason from disease of the mind ✓
- B The accused was unable to conform their conduct to the requirements of the law due to mental disease (irresistible impulse)
- C The accused suffered from a substantial disorder of thought, mood, perception, or will that grossly impaired their judgment
- D The accused's criminal conduct was a product of mental disease or defect (Durham rule)
Correct answer: A. The accused did not know the nature of the act, or did not know it was wrong, due to a defect of reason from disease of the mind
Explanation
The M'Naghten rules require proof that at the time of the act, the accused was labouring under such a defect of reason from disease of the mind that they: (a) did not know the nature and quality of the act; or (b) did know, but did not know that what they were doing was wrong. This is a purely cognitive test that does not include inability to control behaviour (irresistible impulse — American rule) or the 'product' test (Durham rule). Indian law (BNS Section 20) follows the M'Naghten framework, adding the clause 'contrary to law.'
Reference: The Essentials of Forensic Medicine and Toxicology (Narayan Reddy), 34th ed.
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