It is necessary to avoid creating an "unchartable universe of appellate review", as Abella J so picturesquely put it in R v O'Brien 2011 SCC 29 (9 June 2011), writing for herself, McLaughlin CJ, Deschamps, Rothstein, and Cromwell JJ.
So, if a judge says he relies "entirely" on particular evidence, this is not to be taken to mean he was unconsciously influenced by other, inadmissible, evidence. It means the opposite: he deliberately ignored what was inadmissible.
"17. A trial judge has an obligation to demonstrate through his or her reasons how the result was arrived at. This does not create a requirement to itemize every conceivable issue, argument or thought process. Trial judges are entitled to have their reasons reviewed based on what they say, not on the speculative imagination of reviewing courts. As Binnie J. noted in R. v. Sheppard, 2002 SCC 26 (CanLII), 2002 SCC 26, [2002] 1 S.C.R. 869, at para. 55, trial judges should not be held to some "abstract standard of perfection"."
Even so, there can be room for disagreement on appeal about what the judge meant, as occurred in this case. The way to avoid this is for judges to be specific about their treatment of inadmissible evidence, even if counsel had not objected to that evidence at the trial.
