Core principles of criminal liability - Causation in criminal law

Learning Outcomes

After reading this article, you will be able to explain and apply the concept of causation in criminal law, including the distinction between factual and legal causation, the effect of intervening acts, and the operation of the thin skull rule. You will be able to analyse scenarios involving complex chains of events and determine whether criminal liability is established, as required for the SQE1 exam.

SQE1 Syllabus

For SQE1, you are required to understand the principles of causation as part of the core elements of criminal liability. In your revision, focus on:

• the meaning and application of factual causation (the "but for" test)
• the requirements for legal causation (substantial and operating cause)
• the effect of intervening acts (novus actus interveniens), including third-party actions, victim conduct, and medical treatment
• the thin skull rule and its consequences for liability
• how to apply causation principles to realistic problem scenarios

Test Your Knowledge

Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, remember to look more closely at that area during your revision.

1. What is the difference between factual causation and legal causation in criminal law?
2. When will an intervening act break the chain of causation?
3. How does the thin skull rule affect a defendant’s liability?
4. Can negligent medical treatment ever break the chain of causation? If so, when?

Introduction

Causation is a core requirement for criminal liability in result crimes. It ensures that a defendant is only held responsible for a prohibited consequence (such as death or injury) if their conduct actually caused that result. Causation is assessed in two stages: factual causation and legal causation. Both must be satisfied for liability to arise. This article explains the key principles, common pitfalls, and how to apply causation rules in SQE1 scenarios.

Factual Causation

Factual causation asks whether the result would have occurred "but for" the defendant’s conduct. If the answer is yes, factual causation is not established. If the answer is no, factual causation is present.

Key Term: factual causation Factual causation is established if the result would not have occurred but for the defendant’s act or omission.

Worked Example 1.1

A pushes B into a river. B cannot swim and drowns. Would B have died but for A’s action?

Answer: No. B would not have drowned but for A’s push. Factual causation is established.

Legal Causation

Legal causation considers whether the defendant’s conduct was a substantial and operating cause of the result, and whether any intervening act has broken the chain of causation.

Key Term: legal causation Legal causation requires that the defendant’s act is a significant and continuing cause of the result, not merely a minimal or trivial contribution.

Intervening Acts (Novus Actus Interveniens)

An intervening act (novus actus interveniens) is an event that occurs after the defendant’s conduct and contributes to the result. If the intervening act is sufficiently independent and unforeseeable, it may break the chain of causation and relieve the defendant of liability.

Key Term: novus actus interveniens An intervening act is a new, independent event that breaks the causal link between the defendant’s conduct and the result.

Third-Party Acts

A third party’s act will only break the chain if it is free, deliberate, informed, and unforeseeable.

Worked Example 1.2

D stabs V. On the way to hospital, a paramedic crashes the ambulance, and V dies from injuries in the crash. Is D liable for V’s death?

Answer: If the crash was a grossly unforeseeable event, it may break the chain. If the crash was a foreseeable risk of seeking medical help, D remains liable.

Victim’s Own Actions

If the victim’s response is reasonable and foreseeable in the circumstances, the chain is not broken. Only a "daft" or wholly unexpected reaction will break causation.

Worked Example 1.3

D threatens V with violence. V jumps out of a moving car to escape and is injured. Is D liable for V’s injuries?

Answer: If V’s reaction was a foreseeable attempt to escape, D is liable. If V’s response was grossly disproportionate or bizarre, the chain may be broken.

Medical Treatment

Negligent medical treatment will only break the chain if it is so independent and potent in causing the result that the defendant’s contribution is rendered insignificant.

Worked Example 1.4

D stabs V. At hospital, V is given the wrong medication and dies. The original wound was healing. Is D liable for V’s death?

Answer: If the medical error was so gross and the wound no longer life-threatening, the chain may be broken. Ordinary negligence will not usually break causation.

The Thin Skull Rule

The defendant must take the victim as found, including any physical or psychological vulnerabilities.

Key Term: thin skull rule The defendant is liable for the full extent of harm caused, even if the victim has an unusual weakness or condition that makes the result more severe.

Worked Example 1.5

D punches V, who suffers a rare blood disorder and dies. Is D liable for V’s death?

Answer: Yes. The thin skull rule means D is responsible for the unexpected severity of the outcome.

Summary Table: Causation Principles

Key Point Checklist

This article has covered the following key knowledge points:

• Causation is required for result crimes in criminal law.
• Factual causation uses the "but for" test.
• Legal causation requires a substantial and operating cause.
• Intervening acts (novus actus interveniens) may break the chain of causation if they are independent and unforeseeable.
• The thin skull rule means the defendant is liable for the full extent of harm, even if the victim is unusually vulnerable.

Key Terms and Concepts

• factual causation
• legal causation
• novus actus interveniens
• thin skull rule