General Principles of MandamusEdit
An order of mandamus is a common law "prerogative writ" power of a superior court to order a lower court or government agent to perform a mandatory duty correctly. It is a discretionary remedy to compel a lower court to exercise jurisdiction where it has incorrectly refused to do so.
A prerogative writ is a manner of correcting errors of jurisdiction made my inferior courts as well as correcting failures of natural justice or procedural fairness.
When the duty is of a judicial nature, mandamus is not available regardless of whether the decision was incorrect. No superior court can change that decision except for exceptional circumstances such as prejudice, bias, personal interest, dishonesty, and the like.
The order is only available where the body refuses to exercise its jurisdiction.
Despite having jurisdiction, a superior court can refuse prerogative relief if there is an equally effective alternative remedy.
- R. v. MacDonald, 2007 NSSC 255 at 17
- R. v. Forsythe ,  2 S.C.R. 268, 53 C.C.C. (2d) 225
- R. v. Coughlan (1969),  3 C.C.C. 61 (Alta. T.D.) at p. 72
- R. v. Faber, (1987), 38 C.C.C. (3d) 49 (Que. Sup. Ct.) at 54
- Harelkin v University of Regina,  2 SCR 561 at p. 588
General Principles of CertiorariEdit
Certiorari is type of common law writ where the applicant seeks judicial review of a judge's decision by a higher court. It can only be issued when the reviewable court has exceeded its jurisdiction or otherwise a breach of the rules of natural justice, fraud, or an error of law so fundamental a character that it constitutes a defect amounting to a failure or excess of jurisdiction.
It is not sufficient that there be an error on a Charter issue, statutory interpretation, or admissibility/sufficient of evidence. 
It is for this reason that the reviewing court's job is different from that of a court on a straight appeal. 
A successful application of certiorari will quash the reviewed decision of the lower court.
- Patterson v. The Queen (1970), 2 C.C.C. (2d) 227 citing Lord Sumner in R. v. Nat Bell Liquors, Ltd. (1922), 47 C.C.C. 129 (P.C.): :That the superior Court should be bound by the record is inherent in the nature of the case. Its jurisdiction is to see that the inferior Court has not exceeded its own, and for that very reason it is bound not to interfere in what has been done within that jurisdiction, for in so doing it would itself, in turn, transgress the limits within which its own jurisdiction of supervision, not of review, is confined. That supervision goes to two points: one is the area of the inferior jurisdiction and the qualifications and conditions of its exercise; the other is the observance of the law in the course of its exercise.
- Re Madden, et al. v. The Queen (1977), 35 C.C.C. (2d) 381 (Ont. H.C.J.))
- R. v. MacDonald, 2007 NSSC 255
- R v Innocente, 2004 NSCA 18 ("The role of the reviewing judge on an application for certiorari is thus substantially different from that of a judge on appeal. It is only when the judge whose decision is being reviewed has acted in excess of his or her jurisdiction or has breached the principles of natural justice that certiorari will be granted.")
- R. v. Coughlan (1969),  3 C.C.C. 61 (Alta. T.D.) - applicant sought to compel a magistrate to issue a summons or warrant who refused to do so after a hearing. The reviewing judge refused to order the writ as it was a discretionary decision of the magistrate.
- R. v. Faber, (1987), 38 C.C.C. (3d) 49 (Que. Sup. Ct.) - applicant sought to compel the attorney general to withdraw a stay of proceedings against someone charged with murder