Actus reus revisited — causation and omissions

Criminal liability for result crimes requires proof of causation: the defendant's conduct must have caused the prohibited outcome. This divides into factual causation (but-for test: R v White) and legal causation (the conduct must be a substantial and operative cause). Legal causation incorporates the novus actus interveniens doctrine (voluntary intervening acts break the chain), the thin-skull rule (take your victim as you find them), and specific rules on medical treatment. For omissions, English law imposes no general duty to rescue. Liability arises only where a specific duty exists: from statute, contract, special relationship, voluntary assumption of care, creation of danger, or public office (R v Miller). The rationale is to limit criminal responsibility to conduct that fairly attracts blame while preventing liability extending indefinitely through remote consequences or imposing good-Samaritan obligations contrary to individual liberty.

R v White [1910] 2 KB 124: Established the but-for test — the prohibited result must not have occurred but for defendant's act. Fundamental because it sets the minimum threshold for all result crimes.

R v Smith [1959] 2 QB 35: If defendant's act remains an operating and substantial cause, subsequent medical negligence does not break the chain. Critical for establishing that poor medical treatment rarely exculpates defendants.

R v Blaue [1975] 1 WLR 1411: Defendants take victims as they find them, including religious beliefs leading to treatment refusal. Settled the thin-skull principle for all characteristics, not just physical.

R v Miller [1983] 2 AC 161: Creating a dangerous situation generates a duty to take reasonable steps to avert the risk. Fundamentally expanded omissions liability beyond pre-existing relationships.

R v Cheshire [1991] 1 WLR 844: Medical treatment breaks causation only if 'so independent and in itself so potent' that defendant's acts become insignificant. Refined Smith with clearer language.

R v Kennedy (No 2) [2007] UKHL 38: Adult victim's voluntary self-injection of drugs breaks the chain between supplier and death. Crucial limit on drug-supply manslaughter respecting victim autonomy.

Courts apply a two-stage causation analysis. First, factual causation: would the result have occurred anyway at the same time and in the same way? If yes, no liability (White). Second, legal causation: was defendant's act a substantial (more than minimal) and operative (still exerting influence) cause? Multiple causes can co-exist. For intervening acts, ask: was it free, voluntary and informed (Kennedy)? Or a reasonable/foreseeable response (Pagett)? Medical negligence requires the extreme Cheshire threshold. For omissions, identify the specific duty category — courts won't create new duties lightly. Then apply normal causation: would timely action have prevented the result? Judges direct on law; juries apply to facts. Common triggers: drug supply, medical complications, victim flight/self-preservation, refusing treatment, switching off life support.

Stopping at factual causation: Always address both limbs — even obvious but-for causation requires legal causation analysis. Misapplying thin-skull: It covers victim characteristics, not bizarre intervening events — if third party acts, apply novus actus rules. Assuming medical negligence breaks chain: Post-Smith/Cheshire, it almost never does unless 'so independent and potent'. *Ignoring Kennedy in drug cases: Self-injection by autonomous adult breaks chain — but consider Evans* duty if dealer present during overdose. Listing not applying duties: Don't recite categories — explain why each does/doesn't apply to facts. Forgetting causation in omissions: Even with duty, must prove omission caused result.