R v M’Naghten [1843]

1. Facts:

• Scenario: D, suffering from an insane delusion, believed there was a conspiracy against him. Planned to kill Prime Minister Robert Peel but instead killed Peel’s private secretary.

• Outcome: Acquitted of murder; confirmed he was insane.

2. M’Naghten Test:

• Purpose: Establishing insanity.

• Criteria:

◦ Suffering from a defect of reason caused by a disease of the mind meaning either:

▪ Didn’t know the nature/quality of the act, or

▪ Didn’t know the act was wrong.

• Burden of Proof: On D (reverse burden). Presumed sane unless proved otherwise.

3. Impact and Analysis:

• Legal Principle:

◦ Presumption of sanity unless D proves otherwise.

◦ Defect of reason must be from a disease of the mind.

• P. Roberts: Called it an “exceptional historical accident.”

◦ The bar for proving insanity is high, minimising the risk of success in questionable cases.

• Application: Proper use of the test would have likely found D guilty as he understood his act was legally wrong.

4. Alternative Tests:

• Irresistible Impulse Test: Used in jurisdictions like California and Utah.

◦ Criteria: D had an uncontrollable urge to commit the crime and was unable to resist it due to a mental illness.

◦ Consideration: Takes into account D’s mental state.

5. Terms:

• Defect of Reason and Disease of the Mind:

◦ These are legal terms, not psychiatric.

◦ The law doesn’t use medical terms, making it problematic.

◦ D’s delusions must be of the right kind to be acquitted.

6. Implications:

• Challenges: The test may not always align with psychiatric evaluations.

• Legal vs. Medical Terms: The distinction creates complexity, as legal definitions of insanity may not match medical understanding.

In summary, the M’Naghten test sets a stringent legal standard for proving insanity, focusing on the defendant’s understanding of their actions' nature and wrongness. The test, with its reverse burden of proof and reliance on legal rather than medical definitions, aims to minimise questionable acquittals but may not fully accommodate all aspects of mental illness.