What is meant by ‘causation’ in Criminal Law
“Causation" in Criminal Law is concerned with whether the defendant’s conduct contributed sufficiently to the prohibited consequence to justify the criminal liability, which would be assessed from two aspects, namely “factual" and “legal" causation.
Factual causation requires proof that the defendant’s conduct was a necessary condition of the consequence, established by proving that the consequence would not have occurred but for the defendant’s conduct.
The ‘but for’ test was illustrated in the case R v Pagett  where a question was asked that whether the hostage would not have died but for the defendant’s conduct. The factual causation was established as: If the accused had not fired first, the police officers would not have fired their weapons, and then the hostage would not have died.
However, as illustrated in R v White  where the accused by putting cyanide in his mother’s drink was not liable for murder on her death, if the prosecution fails to prove that the defendant’s conduct was a factual cause of the prohibited consequence, then the accused cannot be liable for an offence on that consequence, although he may be still liable for an attempted offence, say attempted murder in R v White.
Legal causation requires proof that the defendant’s conduct was sufficiently connected to its occurrence.  It could be merely established if the defendant’s conduct was an operating and substantial (not trivial) conduct, but not necessarily the only cause of the consequence when there are two or more legal causes of the same consequence.
But difficulties arise when there is something that happened after the defendant’s conduct, i.e. an intervening factor. It should be noted that not every intervening factor amounts to a novus actus interveniens which is ‘voluntary’  and independent thus breaking the chain of causation. Naturally occurring events and reasonably foreseeable events are not generally treated as breaking the chain of causation because of its predictable effect. An objective test as shown in R v Roberts  is adopted in establishing reasonably foreseeable events and it is not necessary to attribute characteristics  of the defendant to the reasonable person. Therefore, the defendant cannot argue that it was the peculiarity  or vulnerable characteristic of the victim that caused the prohibited consequence. The notion ‘take your victim as you find him or her’ is illustrated in R v Blaue  where the defendant was liable for the death of the victim after a blood transfusion. And it was affirmed in many cases that a victim’s failure to seek or follow medical treatment or advice, even ‘unreasonable’  , will not be treated as a novus actus interveniens.  Furthermore, improper or negligent medical treatment, necessitated as a result of the defendant’s infliction of injuries upon the victim, will not break the chain of causation as well. 
The common law principles of causation in Hong Kong was approved in Wong tat Chuen.  Even though one might argue that the Section 65A(1) of the Criminal Procedure Ordinance  changed the objective test (‘infer’ in (a)) into subject test (‘did’ in (b)), because of the title of it as ‘proof of intent’ the statues in fact did not modify the principles in causation and an objective test should still be adopted when establishing the casual link required.
2) Can a person who does not desire or wish a consequence to occur as a result of his voluntary act be said to have intended it? Support your answers with reasons and authorities where appropriate.
The answer to the above question is yes subject to the following explanations.
In the cases where the defendant’s actions amounted to a direct attack upon his victims, the evidence relating to the defendant’s desire or motive will be clear and his intent will have been the same as his desire or motive.
But in some cases, the defendant did a manifestly dangerous act resulting in the death of a victim. The primary desire or motive of the defendant may not have been to harm that person, or indeed anyone, because one may intend to achieve a certain result whilst at the same time not desiring it to come about.
In R v Moloney  , Lord Bridge gave an illustration of the distinction: “A man who, at London Airport, boards a plane which he knows to be bound for Manchester, clearly intends to travel to Manchester, even though Manchester is the last place he wants to be and his motive for boarding the plane is simply to escape pursuit."
In R v Nedrick  , the English Court of Appeal further explained this example as follows:
“The man who knowingly boards the Manchester aircraft wants to go there in the sense that boarding it is a voluntary act. His desire to leave London predominates over his desire not to go to Manchester. When he decides to board the aircraft, if not before, he forms the intention to travel to Manchester."
In R v Nedrick, the appellant was convicted of murder after he poured paraffin through the letter box at the house of a woman to whom he had earlier made the threat to “burn her out". The appellant admitted he had started the fire but he stated that he had not wanted anyone to die. The English Court of Appeal held that the trial judge’s direction to the jury that if the appellant knew “it was highly probable that the act would result in serious bodily injury to somebody inside the house, even though he did not desire it …… he is guilty of murder" was wrong as that equated foresight with intent because, citing R v Moloney, “foresight of consequences, as an element bearing on the issue of intention in murder … belongs, not to the substantive law, but to the law of evidence".
The English Court of Appeal held in R v Nedrick at 270 that:
“Where the charge is murder and in the rare cases where the simple direction is not enough, the jury should be directed that they are not entitled to infer the necessary intention, unless they feel sure that death or serious bodily harm was a virtual certainty (barring some unforeseen intervention) as a result of the defendant’s actions and that the defendant appreciated that such was the case.
Where a man realises that it is for all practical purposes inevitable that his actions will result in death or serious harm, the inference may be irresistible that he intended that result, however little he may have desired or wished it to happen. The decision is one for the jury to be reached upon a consideration of all the evidence."
In R v Woollin  , the House of Lords in the judgment delivered by Lord Steyn approved this direction except that the word “find" should be substituted for the word “infer" for clarity.
The Hong Kong Court of Appeal considered these authorities in SFC v Zou Yisha  and held that the evidential principle now expressed in Nedrick and Woollin as to a defendant’s intent to bring about a certain result being found from his appreciation of the virtual certainty of his actions bringing about that result, is applicable generally in the common law to all offences of specific intent.  .
The Court of Appeal’s remarks in SFC v Zou Yishang at para. 44 are worth noting:
“It follows that the Nedrick and Woollin test has in principle general applicability to all offences of specific intent, though it may well be that it will be relatively few cases where the test is of any practical benefit. Those cases will mostly arise where the offence charged was not the primary purpose of the defendant."
In short, where the defendant appreciated that a consequence of his voluntary act was virtually certain, the jury would be entitled to find that he did intend that consequence even if he did not desire or wish it to occur.