A proper understanding of the term “proof beyond a reasonable doubt” and the rationale for having such a high standard of proof in criminal trials is critical for maintaining confidence in the administration of justice.
The Special Meaning of Proof Beyond a Reasonable Doubt
When a judge or a jury is deciding whether the prosecution has proven an allegation against an accused, the standard for the decision-making process is “proof beyond a reasonable doubt”.
What exactly does it mean for the prosecution to prove something beyond a reasonable doubt?
The term has a specific meaning in the Canadian criminal justice system. It is “an exacting standard of proof rarely encountered in everyday life” (R. v. Starr,  2 S.C.R. 144 at para. 241).
If you are ever called upon to sit on a jury, a judge will draw upon the following language from past decisions of the Supreme Court of Canada to assist you in understanding the term:
The term "beyond a reasonable doubt" has been used for a very long time and is a part of our history and traditions of justice…..
…A reasonable doubt is not an imaginary or frivolous doubt.
It must not be based upon sympathy or prejudice.
Rather, it is based on reason and common sense.
It is logically derived from the evidence or absence of evidence.
Even if you believe the accused is probably guilty or likely guilty, that is not sufficient...
On the other hand you must remember that it is virtually impossible to prove anything to an absolute certainty and the Crown is not required to do so. Such a standard of proof is impossibly high.
If standards of proof were marked on a measure, proof "beyond reasonable doubt" would lie much closer to "absolute certainty" than to "a balance of probabilities"…..the criminal standard is more than a probability….
In short if, based upon the evidence before the court, you are sure that the accused committed the offence you should convict since this demonstrates that you are satisfied of his guilt beyond a reasonable doubt.
(see R. v. Lifchus, , 3 S.C.R. 320 at para. 39 and Starr at para. 242)
The high standard of proof beyond a reasonable doubt serves to protect against the conviction of an innocent person. As stated by the Supreme Court of Canada in Lifchus at para. 13
That jurors clearly understand the meaning of the term is of fundamental importance to our criminal justice system. It is one of the principal safeguards which seeks to ensure that no innocent person is convicted. The Marshall, Morin and Milgaard cases serve as a constant reminder that our system, with all its protections for the accused, can still make tragic errors.
It is often difficult for the prosecution to establish what happened on a particular date with a high degree of confidence. If we are going to make mistakes in the decision-making process, we have decided as a society to err on the side of letting a guilty person walk free as opposed to taking away the liberty of an innocent person.