In criminal law, causation essentially describes a ‘cause and effect’ relationship between the defendant’s actions and the harm suffered by the alleged victim.
In order to establish a defendant’s guilt, the prosecution must prove beyond reasonable doubt that his or her actions were a ‘substantial and significant cause’ of the harm.
This means that although other factors may have contributed to the harm suffered, the defendant can in certain circumstances still be found criminally responsible.
Homicide cases are often useful to illustrate the law relating to causation.
In the important case of Royall v R  HCA 27, Kelly Louise Healey died after falling from the window of a sixth floor apartment.
It was alleged that prior to her death, she had been engaged in a violent argument with her boyfriend, Mr Royall.
At trial, the prosecution put forward three possible explanations for her death:
1. That Mr Royall had pushed her out of the window,
2. That she had fallen whilst attempting to avoid an attack by Mr Royall, and
3. That she died whilst trying to escape ‘life-threatening violence.’
It was held that even though Ms Healey may have directly brought about her own death by jumping out the window, Mr Royall was ultimately responsible for her death as he created a ‘well founded apprehension that she would be subjected to further violence’ if she remained in the apartment.
Accordingly, the court found that Royall’s actions were the ‘substantial or significant cause’ of Ms Healey’s death.
In criminal cases, the question of whether the defendant’s conduct ‘substantially or significantly’ brought about the deceased’s death is left to the jury.
Where there are several different possibilities for the death, as was the case in Royall, the jury is not required to determine the exact cause of death – but rather, they should simply focus on whether the defendant’s actions substantially contributed towards the death.
Issues of causation are not always clear-cut and can be a point of contention in criminal matters.
For example, in the English case of R v Blaue  3 All ER 446, Robert Blaue entered the deceased’s home and asked her for sex. When she refused, he stabbed her numerous times.
Though the deceased’s life could have been saved by a blood transfusion, she refused medical treatment due to her religious beliefs.
She later died as a result of blood loss.
At trial, Blaue’s lawyers argued that it was the deceased’s refusal to accept a blood transfusion that ‘broke the chain of causation’ and caused her death.
However, this argument was rejected and the court found that the stabbing was the ‘substantial and significant’ cause of death.
The court also held that those who commit violent acts on others must take their victims as they find them, and cannot escape liability simply because of the deceased’s religious beliefs.
In another case, R v Hallett  SASR 141, Mr Hallett and the deceased, Mr Whiting, were driving in the sand near a body of water when they became bogged.
An argument ensued and Hallett physically assaulted Whiting.
He then left Whiting slumped on his back at the edge of the water.
At the time that Hallett left the scene, Whiting was still alive, but when he returned some hours later he had died and was floating in the water.
It was suggested that Whiting had died after becoming unconscious and drowning.
The court found that Hallett’s actions were the overriding cause of Whiting’s death, and that he was therefore responsible for the death.
These cases give rise to the principle that the chain of causation can only be broken by a new intervening act.
There are generally two accepted instances where the chain of causation can be broken.
The first is where the person’s death or suffering is caused by a voluntary human act which is unrelated to the defendant’s actions.
The second is where an extraordinary coincidental event occurs which causes the person’s death or suffering.
For example, in the case of Hallett, if Whiting had instead drowned after being hit by an extraordinary tidal wave, the defence team may have been able to argue that the chain of causation had been broken.
It is not always easy to establish a break in the causation chain, and being able to identify problems with the prosecution case in relation to causation often requires the expertise and experience of a leading criminal defence lawyer.