Legal Definitions - M'Naughten rules

The M'Naughten rules are a set of legal principles used in some jurisdictions to determine if a person can be held criminally responsible for their actions, specifically when an insanity defense is raised. These rules establish the criteria for legal insanity, distinguishing it from a medical diagnosis of mental illness. For a defendant to be found legally insane under the M'Naughten rules, it must be proven that, at the time of committing the act, they were suffering from a "defect of reason, from disease of the mind," which caused them to either:

• Not know the nature and quality of the act they were doing; or
• If they did know it, they did not know that what they were doing was wrong.

Essentially, the rules focus on the defendant's cognitive capacity to understand the nature of their actions and whether those actions were legally or morally wrong.

Here are some examples to illustrate the application of the M'Naughten rules:

• Example 1: Delusional Belief About Reality

  Imagine a person, Mr. Henderson, who suffers from severe paranoid schizophrenia. Due to his profound delusions, he genuinely believes that his neighbor is a shape-shifting alien attempting to steal his thoughts and that the only way to protect himself and humanity is to "neutralize" the threat. He attacks his neighbor, believing he is destroying an alien entity, not harming a human being. In this scenario, Mr. Henderson might meet the M'Naughten criteria because, due to a "defect of reason from disease of the mind," he did not know the nature and quality of his act – he perceived his victim as an alien, not a person, and his action as self-defense against an extraterrestrial threat, not an assault on a human.

• Example 2: Inability to Comprehend Wrongfulness

  Consider Ms. Davies, who has a severe psychotic disorder that causes her to experience powerful auditory hallucinations commanding her to perform specific acts, which she perceives as divine directives. She commits an act of vandalism, destroying public property, because the "voices" told her it was a sacred ritual necessary to prevent a global catastrophe. While she physically understands she is breaking windows and defacing walls, her mental illness prevents her from comprehending that her actions are legally or morally wrong in the eyes of society. She believes she is fulfilling a higher, righteous purpose. Here, Ms. Davies might satisfy the M'Naughten rules because, despite knowing the physical nature of her act, her "disease of the mind" prevented her from knowing that what she was doing was wrong.

• Example 3: Misperception of Consequences

  Suppose Mr. Chen, suffering from a severe dissociative disorder, experiences a complete detachment from reality during a psychotic episode. During this episode, he physically assaults someone, but due to his mental state, he genuinely believes he is merely participating in a harmless video game simulation where no real harm can occur. He sees the person he is hitting as a digital avatar and the act as a game interaction, not a physical assault with real-world consequences. In this case, Mr. Chen might be found legally insane under M'Naughten because his "defect of reason" caused him to not know the true nature and quality of his act – he did not understand that he was inflicting actual physical harm on a real person.