R. v. Mayuran, 2012 SCC 31 was just released. It deals with when a defence ought to be put to a jury.
Broadly speaking, a proposed defence to a criminal charge must at least have an evidential foundation before it can be considered by a jury. As the Supreme Court noted in R v Cinous 2002 SCC 29 at ¶51, ¶53 and ¶81:
"The basic requirement of an evidential foundation for defences gives rise to two well-established principles.
"First, a trial judge must put to the jury all defences that arise on the facts, whether or not they have been specifically raised by an accused. Where there is an air of reality to a defence, it should go to the jury.
"Second, a trial judge has a positive duty to keep from the jury defences lacking an evidential foundation. A defence that lacks an air of reality should be kept from the jury.
"… In applying the air of reality test, a trial judge considers the totality of the evidence, and assumes the evidence relied upon by the accused to be true. See Osolin, supra; Park, supra. The evidential foundation can be indicated by evidence emanating from the examination in chief or cross-examination of the accused, of defence witnesses, or of Crown witnesses. It can also rest upon the factual circumstances of the case or from any other evidential source on the record. There is no requirement that the evidence be adduced by the accused.
"The question to be asked by the trial judge in applying the air of reality test is whether there is evidence upon which a properly instructed jury acting reasonably could acquit if it accepted the evidence as true."
In today’s decision the Court holds:
 This Court has held that a defence should only be put to the jury if it has an “air of reality” (R. v. Cinous,  2 S.C.R. 3, at para. 50). The air of reality test imposes two duties on the trial judge: to “put to the jury all defences that arise on the facts, whether or not they have been specifically raised by an accused”; and “to keep from the jury defences lacking an evidential foundation” (Cinous, at para. 51). Whether a defence arises on the evidence of the accused or of the Crown, the trial judge must put the defence to the jury if it has an air of reality (Cinous, at para. 53; R. v. Osolin,  4 S.C.R. 595).
 In determining whether a defence has an air of reality, there must be an examination into the sufficiency of the evidence. It is not enough for there to be “some evidence” supporting the defence (Cinous, at para. 83). The test is “whether there is (1) evidence (2) upon which a properly instructed jury acting reasonably could acquit if it believed the evidence to be true” (Cinous, at para. 65). For defences that rely on indirect evidence or defences like provocation that include an objective reasonableness component, the trial judge must examine the “field of factual inferences” that can reasonably be drawn from the evidence (Cinous, at para. 91).
 The relationship between the air of reality and the defence of provocation was recently considered by this Court in R v. Tran,  3 S.C.R. 350, where Charron J. explained that
[f]or the defence to succeed, the jury must have a reasonable doubt about whether each of the elements of provocation was present. This necessarily requires that there be a sufficient evidential basis in respect of each component of the defence before it is left to the jury: the evidence must be reasonably capable of supporting the inferences necessary to make out the defence before there is an air of reality to the defence . . . . [para. 41]
 There are two elements to the defence of provocation: an objective and a subjective one. The two components were described in R. v. Thibert,  1 S.C.R. 37:
First, there must be a wrongful act or insult of such a nature that it is sufficient to deprive an ordinary person of the power of self-control as the objective element. Second, the subjective element requires that the accused act upon that insult on the sudden and before there was time for his passion to cool. [Emphasis deleted; para. 4]
(See also Tran, at para. 23.)
The objective element of the defence requires that “(1) there must be a wrongful act or insult; and (2) the wrongful act or insult must be sufficient to deprive an ordinary person of the power of self-control” (Tran, at para. 25).