(1).Types of AR
(3). Intervening acts (novus actus interveniens)
Circumstances will only break the chain of causation if they are: (i)an overwhelming cause of death; and (ii) an unforeseeable occurrence.
(a). Victim’s actions: The general rule of causation is that the defendant is liable for the foreseeable consequences of his actions. Therefore, the victim may break the chain of causation if his reaction to the defendant’s initial act is extreme and unforeseeable.( R v. Roberts (1972) 56 Cr App R 95 (CA))
Note: The thin-skull rule is an exception to the rule that the defendant is only liable for the foreseeable consequences of his actions. This provides that a defendant is liable for the full extent of the victim’s injuries even if, due to some abnormality or pre-existing condition, the victim suffers greater harm as a result of the defendant’s actions than the ‘ordinary’ victim would suffer. (Blaue  1 WLR 1411 (CA).) In Blaue, it was held that the thin-skull rule was not limited to physical conditions but included an individual’s psychological make-up and beliefs.
(b).Third parties: There may be a subsequent attack on the victim, for example, or an unsuccessful attempt to assist the victim that worsens his condition or causes fresh injuries. Consider (1) how significant their contribution was to death and (2) whether their actions were foreseeable. The typical situations is the doctor’s negligence in murder case.
(c). Naturally occurring events: principles of foreseeability determine whether a naturally occurring event will amount to an intervening act which breaks the chain of causation. If it is unforeseeable, then could break the chain of causation.
The general rule is that there is no liability in criminal law for omissions. There are exceptions to that rule if there is a duty to act. Such a duty can arise in various ways:
(b).Contract: If a person fails to do something they are bound by contract to do, they will be criminally liable if harm or injury arises from their omission, even though the person harmed was not a party to the contract. (R v. Pittwood (1902) 19 TLR 37 (Assizes))
(c).Special relationships: parent/child, husband/wife and doctor/patient. These are relationships where there is dependence, reliance and responsibility; for example, in Gibbins and Proctor (1919) 13 Cr App R 134 (CA), the first defendant failed to provide food for his child who starved to death. His liability was based upon his omission to fulfil the duty established by the special relationship of father/child.
(d).Voluntary assumption of care: The second defendant in Gibbins and Proctor was the partner of the child’s father. She was also liable for her omission to provide food but liability was based not on the nature of the relationship but because she had previously fed the child but had ceased to do so. A person cannot cast off the duty to act that the voluntary assumption of care imposes.
(e).Dangerous situations created by defendant: The categories of duty are based on common principles of knowledge (that the victim is in need) and reliance (the victim relies upon the defendant for help; the rest of the world relies upon the defendant to be responsible thus precluding their intervention). In R v Miller  2 AC 161 left the door open for further expansion. In R v Khan  Crim LR 830 (CA), consideration was given to whether a drug-dealer whose ‘customer’ had collapsed following self-administration of drugs was under a duty to act by summoning medical assistance.