Causation of Death
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.
Factual and Legal Causation
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" 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"
It is not necessary for a judge to explain to a jury the distinction between legal and factual causation. The jury need only be instructed on deciding "whether the accused's actions significantly contributed to the victim's death".
In terms of evidence, it is not necessary for the Crown to prove the exact mechanism by which death was caused. It is only necessary that it be proven that an unlawful act led to injuries which caused death.
Degree of Participation in Constructive Murder
Where the offence is "constructive murder" under s. 231(5), that there is an added requirement (or enhanced Harbottle standard) that the accused be a "substantial cause of death". Given the nature of first degree constructive murder there is an added degree of participation in the killing to engage s. 231(5). To that end, the Crown must prove the accused "committed an act or series of acts that are of such a nature that they must be regarded as a substantial and integral cause of the deceased’s death. An accused must play a very active role – usually a physical role – in the killing".
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 (CanLII) at paras 71-72
- R v Maybin, 2012 SCC 24 (CanLII) at para 20
- R v Kippax, 2011 ONCA 766 (CanLII),  O.J. 5494 at 22 to 27
- Nette, at para 44
- R v Maybin, 2012 SCC 24 (CanLII) at para 15
- Nette at para 45
- R v Sinclair (T.) et al., 2009 MBCA 71 (CanLII)
R v Stewart, 2003 NSCA 150 at para 30
R v Rahman, 2014 NSCA 67 at para 75
R v Nette at para 73
Tomlinson at para 141
R v Harbottle, 1993 CanLII 71 (SCC),  3 SCR 306, at pp. 323-324
Tomlinson at para 142
Nette at para 61
Tomlinson at para 141
Harbottle, at p. 324
Tomlinson at para 145
R v Ferrari, 2012 ONCA 399 (CanLII), 287 CCC (3d) 503, at para 68
Tomlinson at para 145
Ferrari at para 85
Harbottle at p. 316
Deemed Causation of Death
Death that might have been prevented
224 Where a person, by an act or omission, does any thing that results in the death of a human being, he causes the death of that human being notwithstanding that death from that cause might have been prevented by resorting to proper means.
R.S., c. C-34, s. 207.
Death from treatment of injury
225 Where a person causes to a human being a bodily injury that is of itself of a dangerous nature and from which death results, he causes the death of that human being notwithstanding that the immediate cause of death is proper or improper treatment that is applied in good faith.
R.S., c. C-34, s. 208.
Acceleration of death
226 Where a person causes to a human being a bodily injury that results in death, he causes the death of that human being notwithstanding that the effect of the bodily injury is only to accelerate his death from a disease or disorder arising from some other cause.
R.S., c. C-34, s. 209.
Killing by influence on the mind
228 No person commits culpable homicide where he causes the death of a human being
- (a) by any influence on the mind alone, or
- (b) by any disorder or disease resulting from influence on the mind alone,
but this section does not apply where a person causes the death of a child or sick person by wilfully frightening him.
R.S., c. C-34, s. 211.
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" 
It has been suggested that the intervening should be something that in some way is "extraordinary or unusual".