## Facts

- Mr. Kemp struck his wife with a hammer while unaware of his actions.
- He suffered from arteriosclerosis, a hardening of the arteries, leading to restricted blood flow to the brain.
- The reduced blood flow caused Kemp to experience a brief loss of consciousness, resulting in involuntary behavior.
- Medical evidence confirmed his condition and connected it to the assault on his wife.

## Issues

1. Whether arteriosclerosis qualifies as a "disease of the mind" under the M'Naghten Rules, such that it can support a defense of insanity.
2. Whether the distinction between physical and psychological causes affects the application of the insanity defense.

## Decision

- The Court of Criminal Appeal upheld the trial judge’s finding that arteriosclerosis constituted a "disease of the mind" for legal purposes.
- The court emphasized that the relevant factor is the effect on mental faculties, not the origin (physical or psychological) of the condition.
- It was held that arteriosclerosis, despite being a physical ailment, impaired Kemp’s awareness and self-control sufficient to meet the legal test.
- Lord Devlin stated that the law looks at the result (impairment of mental function), not the source (physical cause).

## Legal Principles

- The definition of "disease of the mind" under the M'Naghten Rules centers on the condition’s impact on mental processes, regardless of medical classification.
- Both physical and psychological conditions can be included if they disrupt normal mental function.
- The legal test focuses on mental impairment and not strictly on medical diagnosis or origin.
- The case distinguished internal medical conditions (e.g., arteriosclerosis) from external causes of automatism, such as drug-induced episodes.
- Subsequent cases, including R v Sullivan [1984] AC 156 (epilepsy) and R v Quick [1973] QB 910 (external factors), have relied on this approach to classify disorders.

## Conclusion

R v Kemp established that conditions impairing mental faculties—regardless of physical or psychological origin—may constitute a "disease of the mind" for the purposes of the insanity defense, shaping modern interpretation of criminal responsibility.


R v Kemp [1957] 1 QB 399