Another answer claims:
It always remains with the prosecution or the plaintiff (P) to prove their case to the required standard; the defendant (D) never has to prove anything. ...
And regarding affirmative defences:
To use one, the D has to raise it, but the onus remains on the P to prove that D's assertion isn't true.
... it sort of seems like the burden has shifted from the P to the D. But it hasn't. The onus of proof still rests with the P to disprove the D's defence.
Is this true?
It is not the norm, but the burden does actually shift to the defence in many circumstances. I present examples from Canada and Australia, but I expect examples can be found in every jurisdiction.
For example, for defamation:
To obtain judgment, the plaintiff must prove three things: i) that the impugned words were defamatory; ii) that they referred to the plaintiff; and iii) that they were published, meaning that they were communicated to at least one other person. Where the plaintiff establishes these elements, falsity and damage are presumed and the onus shifts to the defendant to advance a defence in order to escape liability.
Weaver v. Corcoran, 2017 BCCA 160, para. 70
See also Grant v. Torstar, 2009 SCC 61, para. 29:
If the plaintiff proves the required elements, the onus then shifts to the defendant to advance a defence in order to escape liability.
In a true burden-shifting regime such as this, it is not the case that the plaintiff has any further burden to disprove the elements of the defence. That is: in defamation, the plaintiff has no burden to disprove the truth of the statement. It is presumed to be false and the burden is wholly on the defendant to establish its truth (on a balance of probabilities) in order to avoid liability.
And in strict liability offences, the burden does literally shift to the defendant to prove they acted with due diligence. See R. v. Sault Ste. Marie, [1978] 2 S.C.R. 1299:
Thus while the prosecution must prove beyond reasonable doubt that the defendant committed the prohibited act, the defendant need only establish on the balance of probabilities his defence of reasonable care.
In bail proceedings, for certain serious charges, the accused has the burden of justifying their release pending trial. See Criminal Code, s. 515(6) and Fact Sheet: The Bail Process. If the accused fails to "show[] cause why the accused’s detention in custody is not justified," the accused will be detained.
And some true criminal offences actually place a burden on the accused to prove their innocence, which the Supreme Court of Canada has found to justifiably infringe the presumption of innocence guaranteed by s. 11(d) of the Charter. For example, in R. v. Whyte, [1988] 2 S.C.R. 3, the Court considered the following presumption from the Criminal Code:
where it is proved that the accused occupied the seat ordinarily occupied by the driver of a motor vehicle, he shall be deemed to have had the care or control of the vehicle unless he establishes that he did not enter or mount the vehicle for the purpose of setting it in motion
This was found to reverse the onus and place the burden on the accused to prove their innocence. However, this infringement of the 11(d) Charter right was justified because it served a sufficiently important objective (addressing impaired driving); the provision was rationally connected to that objective; the provision was minimaly impairing; and there was a proportionality between the infringement and the attainment of the objective.
The Australian Law Reform Commission recognizes that "[a] range of Commonwealth laws place a legal burden on the defendant in respect of particular issues."
A number of Commonwealth criminal offences reverse the legal burden of proof and may be seen as interfering with the principle that a person is presumed innocent until proved guilty according to law.
A specific example the Commission provides is drug offences.
when the defendant is found to be dealing with a threshold ‘trafficable’ quantity of a controlled drug, the person is deemed or presumed to have either: the intention to traffic; the intention to cultivate for a commercial purpose; or the intention to manufacture for a commercial purpose.
The legal onus lies on the defendant to defeat these presumptions — that is, the defendant must prove, on the balance of probabilities, that he or she did not have the requisite intention for the offence.
Other examples the Commission presents are terrorism offences, child sex offences outside Australia, taxation, copyright, bail, claims under the Fair Work Act 2009, and discrimination laws. Just as in Canada, the view of the Commission is that reversals of onus in the criminal context are only justified when they are justified under a proportionality analysis.
