Mandamus and prohibition are often described as mirror images of each other.
If mandamus is the writ that compels action, prohibition is its counterpart: the writ that prevents a lower court or tribunal from taking an action it has no legal authority to take.
What prohibition addresses
A writ of prohibition is typically sought when a lower court is about to exercise jurisdiction it does not have — for example, proceeding with a case after a party has been dismissed, or asserting authority over a matter that belongs exclusively to another tribunal.
The shared procedural framework
Because both writs address the conduct of lower courts or officials and share the same historical common-law origin, many jurisdictions apply nearly identical procedural rules to mandamus and prohibition petitions, often filing them under the same rule or statute.
The "no adequate remedy" element in both
Just as mandamus requires no adequate remedy by ordinary appeal, prohibition requires the same showing — that waiting for the lower court to finish the case and then appealing would not adequately address the harm of allowing an unauthorized proceeding to continue.
When the two writs overlap in practice
Some disputes can be framed as either a mandamus or a prohibition claim, depending on how the underlying problem is characterized — for instance, asking a court to stop hearing a claim (prohibition) versus asking it to dismiss the claim (which could be framed as compelling a ministerial dismissal, arguably mandamus). Courts generally look past the label to the practical substance of what is being requested.
Why this distinction still matters procedurally
Even where the underlying jurisdictions and standards are similar, correctly identifying which writ actually fits the relief sought helps ensure the petition is evaluated under the right legal framework from the outset.
The elements each petition has to establish
The two writs are not distinguished by the words used in the caption but by what the petitioner must prove and when the proof has to exist. California states both remedies in statute and the contrast is unusually clean: Cal. Civ. Proc. Code § 1085 authorizes mandate to compel performance of an act the law specially enjoins, while § 1102 defines prohibition as its counterpart, an order arresting the proceedings of a tribunal exercising judicial functions without or in excess of its jurisdiction. Both issue only where there is no plain, speedy, and adequate remedy in the ordinary course of law.
| What the petition must establish | Mandamus | Prohibition |
|---|---|---|
| The right asserted | A clear and indisputable right to have a specific act performed | A clear right not to be subjected to the proceeding at all |
| The respondent's defect | Refusal or failure to perform a duty the law fixes | Exercise of judicial or quasi-judicial power without or beyond jurisdiction |
| The discretion problem | The duty must be ministerial; the writ cannot dictate how discretion is exercised | The excess of jurisdiction must appear on the record; error committed within jurisdiction is not enough |
| When it is sought | After the duty is due and performance has been refused; no rule fixes a deadline, but unexplained delay is a ground for denial | While the proceeding is still pending; once the act is complete there is nothing left to arrest |
| What the order produces | A command to perform the act, enforceable by contempt | An order stopping the tribunal from proceeding further |
| What it never produces | A particular outcome of a discretionary decision | Correction of a ruling the tribunal had power to make |
| Route if the writ is unavailable | Appeal after final judgment, or a delay claim under 5 U.S.C. § 706(1) against an agency | Motion to dismiss for want of jurisdiction, then appeal from the judgment |
Where prohibition is the right writ and mandamus is not
The test is the direction of the complaint. A petitioner who says the tribunal is doing nothing wants mandamus. A petitioner who says the tribunal is doing something it has no power to do wants prohibition, and a mandamus petition in that posture asks the wrong question: there is no unperformed duty to command.
Three situations belong to prohibition. A court is about to try a case the legislature assigned exclusively elsewhere. An agency has scheduled a hearing on a matter outside its enabling act. A tribunal continues to act after its authority has expired. In each, the relief needed is a stop, and it has to arrive before the proceeding ends.
Federal practice blurs the labels without changing the analysis. Fed. R. App. P. 21 governs petitions for writs of mandamus and prohibition together, and 28 U.S.C. § 1651 supplies the power for both, so a court of appeals that wants to stop a district court usually issues a writ directing it to vacate the order or dismiss the case. The label is mandamus; the function is prohibition.
The defenses that defeat both petitions
Neither writ is a second opinion. Will v. United States, 389 U.S. 90 (1967), describes the remedy as drastic and extraordinary, reserved for exceptional circumstances, and Roche v. Evaporated Milk Association, 319 U.S. 21 (1943), confines the supervisory writs to confining a lower court to a lawful exercise of its jurisdiction or compelling it to exercise authority it is bound to exercise. An error made within jurisdiction, however wrong, is not within either writ.
- An adequate ordinary remedy. If the objection can be raised on appeal, both petitions usually fail, whatever the writ is called.
- Contested jurisdictional facts. Prohibition works on a record showing the defect; where jurisdiction turns on disputed evidence, the tribunal decides that question first.
- Discretion to deny. Ex parte Fahey, 332 U.S. 258 (1947), treats these writs as reserved for really extraordinary causes, and the court may withhold either one after every element is satisfied.
- No independent jurisdiction. 28 U.S.C. § 1651 authorizes writs in aid of jurisdiction that already exists. It creates none.
Key points
- Mandamus answers a failure to act; prohibition answers action taken without or beyond jurisdiction.
- Cal. Civ. Proc. Code § 1085 and § 1102 state the two remedies as counterparts, both conditioned on the absence of a plain, speedy, and adequate remedy.
- Prohibition must be sought while the proceeding is live, because a completed act leaves nothing to arrest.
- Fed. R. App. P. 21 and 28 U.S.C. § 1651 cover both writs, so federal courts often reach a prohibitory result through an order labeled mandamus.
- An error committed within jurisdiction belongs on appeal; neither writ reaches it.