Appeal of an Error of Law
Under s.675(1)(a)(ii) and 686(1)(a)(ii), the defence may appeal a conviction on error of law. Under s. 676(1)(a), the Crown may appeal an aquittal on an error of law.
Where there has been an error of law, such as the improper admission evidence, and the evidence may have influenced the trier of fact in reaching its verdict, the conviction must be quashed, irrespective of whether the admissible evidence supports a conviction.
However, the Court may dismiss an appeal and deny any remedy under s. 686(1)(a)(ii), where the court "is of the opinion that no substantial wrong or miscarriage of justice has occurred"(s.686(1)(b)(iii)).
Different Level of Scrutiny
It is an error of law to apply a different level of scrutiny upon defence evidence than crown evidence. There is no deference applied in the same way as that of credibility determinations. Some Courts have recognized this as a "back door" to re-evaluate credibility and so it should be a "difficult argument" to make.
The legal threshold for proving different level of scrutiny is considered "very high" and "difficult to make successfully".
The appellant cannot "simply ... show that a different trial judge might have made a different assessment of credibility, or that the trial judge failed to make some comment that might have been made in assessing the credibility of the complainant and/or the accused ... the appellant must be able to point to something in the reasons for judgment of the trial judge, or potentially elsewhere in the trial record, that ... make it clear that the trial judge had applied different standards in assessing the evidence of the appellant and the complainant".
It is not enough that a different judge would have made a different assessment or that the he did not "say something" regarding a certain aspect of his assessment, or that he failed to spell out the legal principles.
The appellant must "must point to something in the reasons of the trial judge or perhaps elsewhere in the record that make it clear that the trial judge had applied different standards in assessing the evidence of the appellant and the complainant".
- Colpits v The Queen, 1965 CanLII 2 (SCC),  SCR 739
R v Phan, 2013 ONCA 787 (CanLII) at para 29 to 35
Phan at para 31
R v Aird, 2013 ONCA 447 (CanLII) at para 39
R v Cloutier, 2011 ONCA 484 (CanLII), 272 CCC (3d) 291, at paras 86, 93-94
R v Jones, 2013 ONCA 245 (CanLII), at para 8
R v Schell, 2013 ABCA 4 (CanLII), 542 A.R. 1, at paras 34-35
R v Da Costa, 2014 ONSC 1000 (CanLII) at para 9
R v Howe 2005 CanLII 253 (ON CA), (2005), 192 CCC (3d) 480 (Ont.C.A.), at para 59
De Costa at para 9
R v Howe, 2005 CanLII 253 (ON CA) at paras 58 to 59
- Howe at para 59
Matters Appealed as Questions of Law
Errors in law require the appellant to establish not only an error but that "the error (or errors) of the trial judge might reasonably be thought, in the concrete reality of the case at hand, to have had a material bearing on the acquittal". But does not need to go so far as to convince the court that "the verdict would necessarily have been different" 
A Crown appeal of an acquittal, errors in law include:
- making a finding of fact for which there was no evidence;
- where the legal effect of findings of fact or undisputed fact raises a question of law;
- an assessment of the evidence based on a wrong legal principle; and
- a failure to consider all of the evidence in relation to the ultimate issue of guilt or innocence.
The following have been found to be questions of law and so reviewable on the standard of correctness:
- an assessment of the evidence using the wrong legal principle
- failure to consider all evidence in relation to the issue of guilt
- Failure to consider admitted evidence;
- the interpretation of a "legal standard" 
- the reasonableness of grounds, such as in forming grounds of detention
- a judge adds or deducts a requirement to a controlling legal test.
- whether the trial judge failed to deal with the substance of a critical issue
- the weighing and assessing of one or more items of evidence on the basis of an erroneous legal principle
see R v Graveline, 2006 SCC 16 (CanLII),  1 SCR 609 at para 14
R v Duguay, 2007 NBCA 65 (CanLII) at paras 26-27
- see R v JMH, 2011 SCC 45 (CanLII) at paras 24-32
- JMH at paras 24 to 32
- JMH at paras 24 to 32
- R v Mohan, 1994 CanLII 80 (SCC),  2 SCR 9 at 20
R v Araujo, at para 18
- R v Moore, 2012 BCCA 400 (CanLII)
e.g. Canada (Director of Investigation and Research) v Southam Inc, 1997 CanLII 385 (SCC),  1 SCR 748 at para 39
R v Hillgardener, 2010 ABCA 80 (CanLII) at para 19
R v REM, 2008 SCC 51 (CanLII),  3 SCR 3 at para 57
R v A.A., 2015 ONCA 558 (CanLII) at para 65
Despite any finding of an error of law under s. 686(1)(a)(ii), the court may still dismiss the appeal under the curative proviso under s. 686(1)(b)(iii).