Introduction to Actus Reus: Causation and Omissions

Welcome to your study notes for Paper 2: The Criminal Offender. In this chapter, we are looking at actus reus, which is often called the "physical element" of a crime. For most crimes, the prosecution must prove that the defendant did something (an act) that caused a specific result.

However, the law isn't always as simple as "you did a bad thing." Sometimes, you can be liable for not doing something (an omission), or we might need to look very closely at whether your actions actually caused the end result. Don't worry if this seems a bit technical—we will break it down into simple steps!

1. Causation: Linking the Act to the Result

For "result crimes" (like murder or assault under the Offences Against the Person Act 1861), the law must prove that the defendant's conduct actually caused the victim's injury or death. This is called causation. To prove this, we use a two-stage test.

Stage 1: Factual Causation (The "But For" Test)

This is the starting point. We ask: "But for the defendant’s actions, would the consequence have happened anyway?"

  • If the result would have happened anyway, regardless of what the defendant did, then there is no factual causation.
  • Example: If a defendant puts poison in a victim's drink, but the victim dies of an unrelated heart attack before they even touch the drink, the defendant did not factually cause the death.

Stage 2: Legal Causation

Even if factual causation is proven, the law asks if the defendant is legally responsible. The defendant’s act does not have to be the only cause of the result, but it must be more than a minimal cause. Legal terms for this include:

  • The "De Minimis" Rule: The act must be more than a "minimal" link to the consequence.
  • Operative and Substantial: The defendant's act must still be a significant factor at the time the injury or death occurs.

Breaking the Chain (Novus Actus Interveniens)

Sometimes, something happens after the defendant's act that is so major it "breaks the chain" of causation. This is called a novus actus interveniens (a new intervening act). If the chain is broken, the defendant is no longer liable for the final result.

Common things that might break the chain:

  • Acts of a Third Party: If someone else does something completely unpredictable that causes the final result.
  • Medical Treatment: Usually, poor medical treatment does not break the chain unless it is "so palpably wrong" that the defendant's original act is no longer a cause. The law generally protects doctors trying to save lives.
  • The Victim's Own Actions: If the victim does something "daft" or highly unforeseeable to escape, it might break the chain. However, if their reaction is a reasonable response to the threat, the defendant is still liable.
The "Thin Skull" Rule

An important principle is that you must "take your victim as you find them." If a victim has a hidden physical condition or a religious belief that makes an injury much worse, the defendant is still responsible for the full extent of the harm. You cannot blame the victim's frailty for the outcome.

Quick Review: To prove causation, you need both Factual ("But for") and Legal (more than minimal) links. The chain only breaks if an intervening act is major and unpredictable.

2. Liability for Omissions

In English law, the general rule is that you are not liable for a failure to act. This is often called the "No Good Samaritan" rule. You generally do not have a legal duty to save someone who is drowning or call an ambulance if you see someone injured.

However, there are specific exceptions where the law says you must act. If you have a legal duty to act and you fail to do so, you can be found guilty of the actus reus via an omission.

When does a duty to act exist?

There are several ways a legal duty can be created:

  1. A Statutory Duty: An Act of Parliament says you must act. (Example: A driver failing to provide a breath sample under road traffic laws.)
  2. A Contractual Duty: Your job requires you to act to protect people. (Example: A lifeguard who walks away from their post while someone is in trouble.)
  3. A Duty through Relationship: Usually exists between parents and minor children, or between spouses. Parents have a duty to ensure their children are fed and safe.
  4. A Voluntary Assumption of Care: If you take someone into your home and start looking after them, the law says you have "assumed" a duty. You cannot suddenly stop caring for them if they cannot care for themselves.
  5. Creating a Dangerous Situation: If you accidentally do something that creates a danger, you have a legal duty to take reasonable steps to fix it once you become aware of it.
  6. A Duty through Official Position: People in public office (like police officers) may have a duty to protect the public even when they are technically "off duty."

Important Tip: An omission can only lead to a conviction if the crime itself can be committed by an omission. For example, murder and manslaughter can be committed by omissions, but some crimes (like "making off without payment") usually require a positive act.

Key Takeaways for Exam Success

  • Actus Reus usually requires a voluntary act, but can be satisfied by an omission if a legal duty exists.
  • Causation is a two-part process: Factual ("But for") and Legal (more than minimal).
  • The Chain of Causation is very hard to break. Normal medical errors or the victim’s reasonable fear usually won't break it.
  • Omissions are only criminal if the defendant falls into one of the specific duty categories (Contract, Relationship, etc.).
Common Mistakes to Avoid

Mistake 1: Thinking "But for" is the only test for causation.
Correction: You must check for Legal Causation as well! Even if "But for" is met, the act must be more than minimal.

Mistake 2: Thinking that everyone has a duty to help people in trouble.
Correction: In English law, there is no general duty. You only have to act if you have a specific legal duty (like a parent or a contracted worker).

Mistake 3: Confusing actus reus with mens rea.
Correction: Actus reus is the physical part (the act or omission). Mens rea is the mental part (intention or recklessness). These notes only cover the physical part!

Note: For further application, you can use sections 18, 20, and 47 of the Offences Against the Person Act 1861 as examples of "result crimes" where these principles of causation apply.