Canadian Criminal Law/Causation
Certain offences in the criminal code require not only that the offender do a prohibited act along with the requisite mens rea, but also that the act caused a particular result. Criminal responsibility for causation must be established in fact and in law. This makes a distinction between the physical, biological, or medical cause a particular result and the legal boundary that would attribute responsibility to the accused for the result.
The standard to prove causation is the same as between all homicide offences, including murder, manslaughter, operation of a motor vehicle causing death. Likewise, the standard applies equally to offences involving bodily harm.
The criminal standard of causation in criminal matters is that the "accused's conduct be at least a contributing cause of the [result], outside the de minimis range"
Criminal law does not include any issues of contributory negligence nor does it apportion responsibility for harm caused outside of sentencing.
The inference of foreseeability can be rebutted with evidence of intoxication.
- R. v. Nette, 2001 SCC 78,  3 S.C.R. 488, at para. 44
- R v K.L., 2009 ONCA 141 at 17
- R v K.L., 2009 ONCA 141 at 17 citing:
R. v. Smithers, 1977 CanLII 7 (SCC),  1 S.C.R. 506 at p. 519
R. v. Nette, 2001 SCC 78 (CanLII),  3 S.C.R. 488 at paras. 71 and 72
- R v Nette 2001 SCC 78 at para. 49
R. v. K. L., 2009 ONCA 141 at 18
- R. v. Seymour, 1996 CanLII 201,  2 SCR 252 at para. 23
See R. v. Daley, 2007 SCC 53,  3 SCR 523 for details on the law of intoxication
Causation in Homicide
Homicide is defined in s.222(1) as occurring where a person "directly or indirectly, by any means, ... causes the death of a human being.". Culpable Homicide (i.e. murder, manslaughter, or infanticide) is defined in section 222(5) as "when [a person] causes the death of a human being...by means of an unlawful act".
Causation is explicitly identified as existing where the death might have been otherwise "been prevented by resorting to proper means"(s. 224) or where the immediate cause of death is proper or improper treatment applied in good faith (s.225) or where the victim is already suffering from a terminal condition. (s 226)
The "Smithers test" for causation applies to all types of homicide. The test requires that the accused's act be a "significant contributing cause" of death beyond something trifling or minor. Thus, the unlawful act remains the legal cause of death even where the act by itself would not have cause death as long as it was beyond the de minimus. 
By implication, causation is in no way limited to a direct, an immediate, or the most significant cause.
Where the offence is "constructive murder" under s. 231(5), that there is an added requirement.
A distinction is made between factual causation and legal causation. The former being the broader of the two.
- Factual causation requires "an inquiry about how the victim came to his or her death, in a medical, mechanical, or physical sense, and with the contribution of the accused to that result" (Nette, at para. 44) To put it simply, the question is "but for" the act would death have arose? 
- Legal Causation addresses the moral element of whether the accused "should be held responsible in law for the death"
- R v Smithers, 1977 CanLII 7,  1 SCR 506 - defines manslaughter as “a contributing cause of death, outside the de minimis range” (p. 519)
R v Nette 2001 SCC 78 at 71-72
- R. v. Maybin, 2012 SCC 24 at para 20
- R v Nette at 73
- R. v. Kippax, 2011 ONCA 766,  O.J. 5494 at 22 to 27
- R. v. Maybin, 2012 SCC 24 at para 15
- Nette at para. 45
The doctrine of intervening acts can limit the scope of legal causation. The law recognizes an intervening cause that "'break the chain of causation' between the accused's acts and the death" which results in the "accused’s actions not being a significant contributing cause of death" 
- R v Tower 2008 NSCA 3 at para 25
- R. v. Kippax, 2011 ONCA 766 at 21-28