Canadian Criminal Law/Principles of Interpretation
Principles of Statutory Interpretation 
The fundamental principle of statutory interpretation is that "the words of a statute be read in their entire context and in their grammatical and ordinary sense harmoniously with the scheme of the Act, the object of the Act, and the intention of the legislature"
It is understood that legislators choose to adopt “language which accurately conveys the effect of the law without in itself imposing an unnecessary burden of translation and explanation”.
The principle of legality requires that legislation provide a degree of certainty, and should reflect “the overall need to use the criminal law with restraint”
No provision in an act "should be interpreted so as to render it mere surplusage.”
Under s. 12 of the Interpretation Act, "[e]very enactment is deemed remedial, and shall be given such fair, large and liberal construction and interpretation as best ensures the attainment of its objects."
It is a principle that "Parliament does not speak in vain".
"[A]bsent express language to the contrary, the same words in two subsections of the same provision should be treated alike... Giving the same words the same meaning throughout a statute is a basic principle of statutory interpretation".
- Rizzo & Rizzo Shoes Ltd. (Re), 1998 CanLII 837 (SCC),  1 S.C.R. 27, at para. 21
Bell Expressive Limited Partnership v. Rex, 2002 SCC 42,  2 S.C.R. 559, at para.26
R v Brode, 2012 ONCA 140, (“direct that the words of a statute be read in their entire context and in their grammatical and ordinary sense harmoniously with the scheme of the Act, the object of the Act, and the intention of the legislature.”)
- Howard’s Criminal Law (5th ed. 1990), at p. 11
- see D. Stuart, Canadian Criminal Law: A Treatise (5th ed. 2007), at p. 86
- R. v. Proulx 2000 SCC 61 at 25
- R.S., c. I-23, s. 11.
- Attorney General of Quebec v. Carrières Ste-Thérèse Ltée, 1985 CanLII 35 (SCC),  1 S.C.R. 831, at p. 838
- R. v. Charette, 2009 ONCA 310 at para. 38 citing R. v. Zeolkowski, 1989 CanLII 72 (SCC),  1 S.C.R. 1378 at p. 1387
Charter Interpretation 
- R v Brydges  1 S.C.R. 190
- Hunter v. Southam Inc., 1984 CanLII 33 (SCC),  2 S.C.R. 145
R. v. Big M Drug Mart Ltd., 1985 CanLII 69 (SCC),  1 S.C.R. 295
Amendments generally only have retrospective effect in exceptional circumstances. As there is a presumption against retrospectivity where a vested or substantive right is affected.
Where an amendment to legislation effects a constitutional right, it generally means that the legislation will not be retrospective.
An amendment that has an effect on the content or existence of an available defence suggests is an indicator that it affects substantive rights, and so is not retrospective.
An increase in a maximum penalty is a "clear indication to sentencing courts of the seriousness which the criminal conduct addressed by the changes is viewed by contemporary society."However, the increase of minimum penalties should not be read into "too much".
Effect on Previous Ongoing Proceedings 
Where the law is changed in a manner that is procedural in nature, it applies to all matters regardless of the offence date. A change in the law that removes or adds a right will only apply to offences that post-date the amendment.
It is "not generally in the public interest to delay trials simply on the basis that a pending action in the higher courts might have some effect on the trial".
- R v Wildman (1984) 14 CCC (3d) 321
See also: R v Bickford (1989) 51 CCC (3d) 181 (ONCA)
- R v Baker  NSJ 135 (NSCA)
Stare Decisis 
The principle of stare decisis refers to the requirement that when a legal issue has been determined and decided other courts should follow the decision.
The principle is the "glue that holds together the various levels of Canadian courts and it is the principle that elevates the rule of law above the rule of individual judges." It is considered "essential to law" and a "central pillar" to our system of law. It ensures predictability without which differing results would be unjust.
English common law sets out three exceptions of the principles of stare decisis.
- "The court is entitled and bound to decide which of two conflicting decisions of its own it will follow"
- "The court is bound to refuse to follow a decision of its own which, though not expressly overruled, cannot, in its opinion, stand with a decision of the House of Lords";
- "The court is not bound to follow a decision of its own if it is satisfied that the decision was given per incuriam, for example, where a statute or rule having statutory effect which would have affected the decision was not brought the attention of the earlier court"
When considering overruling a precedent from the Supreme Court, the Court should balance the importance of correctness and certainty, considering whether it is more important to maintain certainty with the precedent or ensure correctness by changing it. The Court should be satisfied that there are compelling reasons the precedent should be overruled. 
Ratio Decidendi and Obiter 
Each statement of a judge should not be treated as if it were legislation.
Ratio decidendi ("ratio") and obiter dicta ("obiter") are the terms used to distinguish between binding statements of law and commentary within a decision.
Any judicial comment in a decision that forms part of the rationale to reach his decision is considered part of the ratio and is binding upon lower courts.
A comment by a judge in a decision that does not form part of the rationale to reach his decision is considered obiter. Judicial comments that are obiter do not have binding authority on lower courts. Obiter can have persuasive authority, however.
This distinction between ratio and obiter can be fluid.
The degree of weight the obiter has is proportionate to its proximity to the ratio decidendi.
Stated negatively, the statements of a higher court are not binding where the words are "sufficiently tangential to the disposition of the case".
On the outer edge from the ratio consists of "commentary, examples or exposition that are intended to be helpful, but are certainly not 'binding'". 
The purpose of this distinction is to both promote certainty in the law as well as permit "growth and creativity".
- R. v. Henry, 2005 SCC 76 ("The notion that each phrase in a judgment of this Court should be treated as if enacted in a statute is not supported by the cases and is inconsistent with the basic fundamental principle that the common law develops by experience.")
- R. v. Henry, 2005 SCC 76 at paras. 52-59 ("All obiter do not have, and are not intended to have, the same weight. The weight decreases as one moves from the dispositive ratio decidendi to a wider circle of analysis which is obviously intended for guidance and which should be accepted as authoritative. ")
- Canada (Attorney General) v. Bedford, 2012 ONCA 186 (CanLII) at para. 69
R. v. Prokofiew, 2010 ONCA 423 (CanLII), aff’d 2012 SCC 49 (CanLII)
See Also