La présomption de non-rétroactivité et son fondement
 The leading and most recent authority on the presumption against retrospectivity is the Supreme Court decision in R. v. Dineley, 2012 SCC 58 (CanLII),  3 S.C.R. 272. In Dineley, the court was divided four to three over whether Parliament’s repeal of the “Carter defence” in the drinking and driving context was applicable to – and therefore removed the defence from – defendants who were tried post-amendment, but allegedly committed offences pre-amendment. The court was unanimous on the governing principle, expressed by the majority at para. 10 (and adopted by the dissent at paras. 45-47):
New legislation that affects substantive rights will be presumed to have only prospective effect unless it is possible to discern a clear legislative intent that it is to apply retrospectively…. However, new procedural legislation designed to govern only the manner in which rights are asserted or enforced does not affect the substance of those rights. Such legislation is presumed to apply immediately to both pending and future cases.
 Applying this principle, the court was divided over whether the amendment was properly characterized as affecting substantive or procedural rights. The majority concluded the amendment affected substantive rights and therefore applied strictly prospectively. Accordingly, the former Carter defence was available to those persons alleged to have committed offences prior to the amendment, even if their trials took place after the amendment. Conversely, the minority concluded the amendment was procedural and therefore retrospectively removed the defence from all persons tried after it came into force.
 Deschamps J., writing for the majority, at para. 10., explained the principle that animates the presumption against retrospectivity: “Because of the need for certainty as to the legal consequences that attach to past facts and conduct, courts have long recognized that the cases in which legislation has retrospective effect must be exceptional.”
 In Carriere, Wakeling J. referred to the policy rationale behind the presumption, at para. 57, as described in Sullivan on the Construction of Statutes, 5th ed. (Markham: LexisNexis, 2008):
Perhaps the most fundamental tenet of the rule of law is that those who are governed by the law must have knowledge of its rules before acting; otherwise, any compliance with the law on their part is purely accidental. Citizens must have knowledge of the law before acting so that they can adjust their conduct to avoid undesirable consequences and secure desirable ones. To ensure adequate notice, the rules enacted by the legislature must be published and adequately publicized – ideally before commencement but at the latest upon commencement.… Citizens cannot comply with, rely on or take advantage of law unless they know what it is before deciding how they will behave.
Existe-t-il une exception à la présomption de non-rétroactivité dans des circonstances où la loi est plus bénéfique pour l’accusé?
 The appellants argue that the presumption against retrospectivity does not apply when an amendment confers a benefit to accused persons. They cite the Supreme Court’s decision in Brosseau v. Alberta Securities Commission, 1989 CanLII 121 (SCC),  1 S.C.R. 301, in which L’Heureux-Dubé J. stated, at p. 318, “The so-called presumption against retrospectivity applies only to prejudicial statutes. It does not apply to those which confer a benefit.”
 In my view, the appellant’s reliance on this statement is misplaced. First, the statement was obiter, as the statute in question in that case was categorized neither as beneficial nor as prejudicial, but as falling within a third category of statutes that impose a penalty in order to protect the public, rather than to impose further punishment. It was this third category of statutory provisions that was held to be exempt from the presumption against retrospectivity in Brosseau. The self-defence provisions cannot be said to fall into this category.
 Further, L’Heureux-Dubé J. explicitly distinguished between the aspect of retrospectivity the court was addressing in Brosseau and the aspect at issue in this case, at p. 317:
The basic rule of statutory interpretation, that laws should not be construed so as to have retrospective effect, was reiterated in the recent decision of this Court in Angus v. Sun Alliance Insurance Co., 1988 CanLII 5 (SCC),  2 S.C.R. 256. That case, however, dealt with the question of the retrospective effect of procedural versus substantive provisions. The present case presents a different facet of the problem of retrospectivity.
 Based on this distinction, the present case is like Angus and, therefore, cannot be decided simply on the basis of Brosseau.
 Second, no other Supreme Court decision has distinguished between beneficial and prejudicial statutes based on the comments in Brosseau or otherwise. Not only is there no reference in Dineley that the presumption against retrospectivity is restricted to prejudicial statutes, as will be discussed below, the focus on the effect of a statute to determine its retrospectivity is contrary to the analysis mandated by the Supreme Court in Dineley.
 In any event, the Citizen’s Arrest and Self-defence Act changes the law of self-defence in a manner that is prejudicial to some accused and beneficial to others, depending on their particular circumstances. Therefore, a distinction between prejudicial and beneficial statutes is of no assistance in conducting an analysis of the retrospectivity of this statute.
Pour aussi R. c. Clarke,  1 RCS 612.