Under s. 686(1)(a)(i), the defence may appeal a conviction where there was an "unreasonable or cannot be supported by the evidence". This is one of several grounds of appeal based on evidence. The most frequent is on the grounds of an error of law.
In an unreasonable verdict appeal, the appellate court engages in a review of the facts to determine reasonableness, which includes some reweighing" of the evidence.
The review is an "independent" assessment of facts. It is done "through the lens of judicial experience", which can highlight certain frailties of evidence that may not have been fully appreciated by the trial judge. The review is supposed to be an additional "safeguard against conviction of the innocent".
The review of a judge's reasons is not supposed to be a "line-by-line treature hunt for error".
Basis of Unreasonable Verdicts
Case law has developed three main types of unreasonableness which can form the grounds of an appeal:
- "the evidence as a whole is such that a reasonable jury, properly instructed and acting judicially, could not have reached the verdict"
- "fact findings on material matters of a decisive character are clearly wrong" or
- "whether the reasoning process used by the judge to get from the evidence to the verdict does not make sense in the way described ...in logic"
"686. (1) On the hearing of an appeal against a conviction or against a verdict that the appellant is unfit to stand trial or not criminally responsible on account of mental disorder, the court of appeal
- (a) may allow the appeal where it is of the opinion that
- (i) the verdict should be set aside on the ground that it is unreasonable or cannot be supported by the evidence,..."
NB: this is not an available ground of appeal for the Crown
- (a) may allow the appeal where it is of the opinion that
R v PLS,  1 SCR 909, 1991 CanLII 103 (SCC), per Sopinka J ("In an appeal founded on s. 686(1)(a)(i) the court is engaged in a review of the facts.")
R v Baltovich, 2004 CanLII 45031 (ON CA), (2004), 191 CCC (3d) 289 at para 154 per "The Court"
Biniaris, supra at paras 40 to 41
R v Burke,  1 SCR 474, 1996 CanLII 229 (SCC) at para 6 per Sopinka J.
R v AS, 2016 SKCA 166 (CanLII) at para 23
R v G(DJ), 2012 ABCA 336 (CanLII) at para 8 per Hunt JA.
R v Fleig, 2014 ABCA 97 (CanLII)
R v Roasting, 2016 ABCA 138 (CanLII), at para 13 to 14
Properly Instructed Jury
Unreasonable Verdict (Yebes/Biniaris Test)
The standard of review for unreasonable verdict is where the verdict is one that "no properly instructed jury, acting judicially, could reasonably have rendered".
A verdict that is unreasonable must be one where the judge "revealed he or she was not alive to an applicable legal principle, or entered a verdict inconsistent with the factual conclusions reached.
The applicable test for unreasonable verdict "requires the appeal court to determine what verdict a reasonable jury, properly instructed, could judicially have arrived at, and, in doing so, to review, analyze, and within the limits of appellate disadvantage, weigh the evidence." Or to put it another way: "whether on the whole of the evidence the verdict is one that a properly instructed jury, acting judicially, could reasonably have rendered"
The test does not concern itself with whether the verdict was the only reasonable verdict, but whether it was a reasonable verdict.
Section 686(1)(a)(i) requires the reviewing court to "engage in a thorough re-examination of the evidence" to decide whether "on all the evidence, the verdict was a reasonable one." The verdict must be one that was open to the jury to consider. It is not an error for the judge to simply take a different view of the evidence than the jury.
A court of appeal must not merely substitute its view for that of the jury but in applying the Yebes test is entitled to review, analyze and, within the limits of appellate disadvantage, weigh the evidence. 
The test applies equally to a jury and a judge sitting alone. In the latter case, the review may be easier because the appellate court will be able to examine the reasons provided by the judge, which may reveal a flaw in the evaluation of the evidence. Such a deficiency in analysis may appear where a judge was not alive to an applicable legal principle or entered a verdict inconsistent with the factual conclusions reached. 
A reviewing court must articulate the basis upon which it finds that the conclusions reached by a jury were unreasonable. A lurking doubt or vague unease based on the court’s review is not sufficient justification for a finding of unreasonableness but may trigger increased appellate scrutiny. 
A jury does not provide reasons for its verdict. To justify a finding of unreasonableness regarding the verdict of a properly instructed jury, the appeal court will not be able to point to express deficiencies in analysis. It must fall back upon and articulate inferences drawn from a review of the evidence to support its conclusion that the jury, in arriving at its guilty verdict, could not have been acting judicially. 
Jury instructions attempt to convey accumulated judicial experience to the jury. Still, in certain rare cases, the totality of the evidence and the peculiar factual circumstances will lead an experienced, legally trained, jurist to conclude that the fact-finding exercise applied at trial must have been flawed in light of the unreasonable results it produced. 
Acting judicially, in this context, means not only acting dispassionately in applying the law and adjudicating on the basis of the law and nothing else. It means, in addition, arriving at a conclusion that does not conflict with the bulk of judicial experience. The reviewing court’s assessment must, in other words, proceed through “the lens of judicial experience” to identify and articulate, as precisely as possible, those features of the case which suggest that the verdict was unreasonable. There may be several causes of concern, none of which, in isolation, might have required a particular warning to the jury. 
The reviewing court "must articulate the basis upon which it concludes that the verdict is inconsistent with the requirements of a judicial appreciation of the evidence."
Reading Judgement as a Whole
The reasons should be read as a whole, and not held to a standard of perfection nor should it be the equivalent of jury instructions. The reasons for judgement should never be "read or analyzed as if they were instructions to a jury".
It is inappropriate to "simply plucking colloquial elements" from a trial judge's "thorough reasons" or to "cherry pick" infelicitous phrases.
A judge's decision should not be analysed by "dissecting them into small pieces and examining each piece in isolation". 
An error of the trial judge in finding an acquittal, once found, can only result in a new trial being ordered where the error had “a material bearing on the acquittal”
Errors in Judgement
A mere misstatement at "one point should not vitiate his ruling if the preponderance of what was said shows that the proper test was applied and if the decision can be justified on the evidence."
Courts are given great deference when considering whether findings are supported by the evidence.
The reviewing court should avoid re-visit the trial judge's assessments of the evidence including "discrepancies and then “cherry pick” bits and pieces that may be favourable to the accused.".
On a circumstantial case, the reasonableness of the case will depend on "inferences reasonably available from the totality of the evidence" and whether the "Crown’s ultimate burden to demonstrate that guilt is the only reasonable inference to be drawn from the totality of that evidence".
When a properly instructed jury returned a verdict and that is perceived "to be unreasonable conviction, the only rational inference,… is that the jury, and arriving at that guilty verdict, was not acting judicially" resulting in an overturning of the verdict.
R v Biniaris, 2000 SCC 15 (CanLII),  SCR 381, at para 36 per Arbour J
R v Li, 2013 ONCA 81 (CanLII) at para 123 per Watt JA
R v Sinclair, 2011 SCC 40 (CanLII),  3 SCR 3, at para 4 per Fish J (dissent) and para 44 per LeBel J (concur.)
R v Jackson, 2007 SCC 52 (CanLII),  3 SCR 514, at para 2 per Fish J
- Binaris, supra at para 37
- Biniaris at para 36
R v Yebes, 1987 CanLII 17 (SCC),  2 SCR 168 per McIntyre J
See also R v R.P.
- R v Portillo, 2003 CanLII 5709 (ON CA), (2003), 174 O.A.C. 226, 176 CCC (3d) 467 (C.A.) per Doherty JA
- R v A.G., 2000 SCC 17 (CanLII) at para 6 per L’Heureux-Dube J
- A.G., supra at para 6
R v Rhyason, 2007 SCC 39 (CanLII),  3 SCR 108 at para 10 per Abella J
R v Sheppard, 2002 SCC 26 (CanLII),  1 SCR 869 at para 55 per Binnie J
see also, R v Gagnon, 2006 SCC 17 (CanLII),  1 SCR 621, at para 19
R v REM, 2008 SCC 51 at para 16 (“read as a whole, in the context of the evidence, the issues and the arguments at trial, together with ‘an appreciation of the purposes or functions for which they are delivered’”)
R v Villaroman, 2016 SCC 33 at para 15
R v Laboucan, 2010 SCC 12 (CanLII),  1 S.C.R. 397, at para. 16
R. v C.L.Y., 2008 SCC 2 (CanLII),  1 S.C.R. 5, at para. 11
R. v Morrissey (1995), 1995 CanLII 3498 (ON CA), 22 O.R. (3d) 514, at p. 525
R v Villaroman, 2016 SCC 33 at para 15 per Cromwell J
- R v Davis, 1999 CanLII 638 (SCC),  3 SCR 759 per Lamer CJ (inappropriateness of “simply plucking colloquial elements [from a] trial judge's thorough reasons” )
- R v Morrissey, 1995 CanLII 3498 (ON CA),  O.J. No. 639 (C.A.) per Doherty JA at para 28 ("[I]t is wrong to analyze a trial judge's reasons by dissecting them into small pieces and examining each piece in isolation as if it described, or was intended to describe, a legal principle applied by the trial judge. Reasons for judgment must be read as a whole.")
- R v Graveline, 2006 SCC 16 (CanLII) at para 14
- R v B. (C.R.), 1990 CanLII 142 (SCC),  1 SCR 717, at p. 737
R v W. (R.), 1992 CanLII 56 (S.C.C.),  2 SCR 122
R v Burke, 1996 CanLII 229 (S.C.C.),  1 SCR 474)
R v Dow, at paras 8, 12
R v Wills, 2014 ONCA 178 (CanLII) at para 33
- R v Effert, 2011 ABCA 134 (CanLII)
Clearly Wrong Findings
A verdict may also be unreasonable if the trial judge draws an inference or makes an essential finding of fact essential to the verdict that:
- is plainly contradicted by the evidence relied on by the trial judge in support of that inference or finding; or
- is shown to be incompatible with evidence that has not otherwise been contradicted or rejected by the trial judge.
Misapprehension of Evidence
In most cases, the proper remedy for an unreasonable verdict resulting in a conviction is an acquittal.