Defending subject-matter jurisdiction: keeping the case in federal court

You filed in federal court. The defendant has moved to dismiss under Rule 12(b)(1), arguing the court lacks subject-matter jurisdiction. Your response brief has to do three things: identify the precise jurisdictional theory you are invoking (diversity, federal question, or supplemental), build the record to support it, and distinguish the kind of attack the defendant is making (facial or factual), because the standards diverge sharply. The plaintiff bears the burden of establishing subject-matter jurisdiction, but that burden is meaningfully different from the merits burden, and the response brief should keep the two separate.

Subject-matter jurisdiction is non-waivable and can be raised at any time, even on appeal. That makes a 12(b)(1) motion especially serious: a dismissal at this stage usually means the case has to be refiled in state court, sometimes after limitations have run on overlapping state claims. A well-briefed response normally either defeats the motion outright or, in the alternative, secures an opportunity to amend and cure jurisdictional defects.

Facial vs. factual attacks

The single most important threshold question is whether the defendant is mounting a facial or a factual attack on jurisdiction.

A facial attack challenges the sufficiency of the jurisdictional allegations in the complaint. The court accepts those allegations as true, much as it does on a 12(b)(6) motion, and asks whether they would, if true, establish jurisdiction. No extrinsic evidence is considered.

A factual attack challenges the truth of the jurisdictional allegations. The court may consider evidence outside the pleadings (affidavits, documents, testimony), and the plaintiff bears the burden of proving jurisdiction by a preponderance. Jurisdictional discovery is available, and the court may hold an evidentiary hearing.

The response brief should identify which kind of attack the defendant has launched, and brief accordingly. Defense briefs sometimes blur the distinction. A facial attack supported by extrinsic affidavits is procedurally improper unless converted into a factual attack with appropriate discovery. If the defendant has attached affidavits, ask the court to treat the motion as factual and to permit jurisdictional discovery before ruling.

Diversity jurisdiction

Diversity jurisdiction under 28 U.S.C. § 1332 requires complete diversity of citizenship and an amount in controversy exceeding $75,000, exclusive of interest and costs.

The complete-diversity rule

The complete-diversity rule traces to Strawbridge v. Curtiss, 7 U.S. (3 Cranch) 267 (1806), which held that the diversity statute requires that no plaintiff share citizenship with any defendant. The rule has survived two centuries of statutory revision and remains the threshold test.

A response brief defending diversity jurisdiction should:

Plead the citizenship of each plaintiff and each defendant. For individuals, that means domicile, not residence. For corporations, that means both state of incorporation and principal place of business. For LLCs and partnerships, that means the citizenship of each member or partner, traced through if necessary.
Confirm that no plaintiff shares citizenship with any defendant.
Address any nominal, fraudulently joined, or stateless parties whose citizenship might disrupt diversity.

Fraudulent joinder is a common defense theory: the defendant argues that an in-state defendant was joined solely to defeat diversity and should be ignored for jurisdictional purposes. The plaintiff defending against a fraudulent-joinder argument must show that there is at least a possibility of recovery against the in-state defendant under state law. The standard is plaintiff-friendly; doubts go to the plaintiff.

Amount in controversy

The amount in controversy is determined from the plaintiff's good-faith allegations. St. Paul Mercury Indemnity Co. v. Red Cab Co., 303 U.S. 283 (1938), set the standard: the plaintiff's allegation controls unless it appears to a legal certainty that the claim is for less than the jurisdictional amount. The legal-certainty standard is demanding; mere doubt about whether the plaintiff will recover the amount alleged is not enough.

In a removed case, the defendant bears the burden of showing that the amount in controversy exceeds the threshold. The response brief should review the notice of removal carefully and identify any failure to meet that burden.

Removal versus original jurisdiction

A case filed originally in federal court is evaluated as of the time of filing. A removed case is evaluated as of the time of removal. The distinctions matter for amount-in-controversy disputes, for post-filing changes in citizenship, and for the strict construction of the removal statute. Caterpillar Inc. v. Williams, 482 U.S. 386, 392 (1987), confirmed that the removal statute is strictly construed in favor of remand.

If the case was removed and the response brief is opposing a remand-by-another-name 12(b)(1) motion, the strict-construction principle should be foregrounded.

Federal question jurisdiction

Federal question jurisdiction under 28 U.S.C. § 1331 reaches civil actions "arising under" federal law. The well-pleaded complaint rule controls: jurisdiction exists only where a federal question appears on the face of the plaintiff's complaint, not in an anticipated federal defense.

Grable and embedded federal questions

A federal question may exist even where the cause of action is created by state law, if the state-law claim necessarily raises a substantial federal issue. Grable & Sons Metal Products, Inc. v. Darue Engineering & Manufacturing, 545 U.S. 308 (2005), held that federal question jurisdiction over state-law claims exists where the federal issue is "(1) necessarily raised, (2) actually disputed, (3) substantial, and (4) capable of resolution in federal court without disrupting the federal-state balance approved by Congress." Id. at 314.

Grable itself involved a state-law quiet-title action that turned on whether the IRS had complied with federal notice requirements. The federal issue was the only contested issue and was dispositive. Jurisdiction was proper.

A response brief invoking Grable should show all four factors:

The federal issue is necessarily raised by an element of the state-law claim.
The parties actually dispute the federal issue.
The federal issue is substantial, in the sense that it implicates an important federal interest, not just a routine application of federal law to a single dispute.
Federal jurisdiction would not upset the congressional allocation of cases between federal and state courts.

Gunn and the narrowness of Grable

Gunn v. Minton, 568 U.S. 251 (2013), tightened the Grable analysis. The Supreme Court held that a state-law legal-malpractice claim against a patent attorney did not satisfy the substantiality requirement, even though resolution required a hypothetical application of patent law, because the federal issue was specific to the parties and did not affect the development of federal patent law more broadly. Id. at 260-64.

Gunn is the case defendants cite when arguing that the federal issue in the plaintiff's complaint is not substantial enough for Grable jurisdiction. The response brief should distinguish Gunn by showing that the federal issue here has broader implications: that it will be precedential, that it affects federal regulatory programs, or that it implicates the uniform interpretation of federal law.

If the case is closer to Gunn than to Grable, candor matters. Consider whether an alternative jurisdictional basis (diversity, supplemental, or a free-standing federal claim) is available, and rest the response on that basis rather than overstating Grable.

Supplemental jurisdiction

Supplemental jurisdiction under 28 U.S.C. § 1367 reaches state-law claims that form part of the same case or controversy as a claim within the court's original jurisdiction. The statute codified and somewhat broadened the pre-1990 judge-made pendent and ancillary jurisdiction doctrines.

The response brief defending supplemental jurisdiction should:

Identify the anchor claim within the court's original jurisdiction.
Show that the state-law claims arise from the same common nucleus of operative fact.
Address any of the statutory exceptions in § 1367(c) that the defendant has invoked (novel or complex state-law issue, state claim substantially predominates, court has dismissed all claims with original jurisdiction, or other exceptional circumstances).

Where the defendant argues that the court should decline supplemental jurisdiction under § 1367(c) even if it exists, the response brief should remind the court that § 1367(c) is discretionary and that retaining jurisdiction often serves judicial economy, especially when discovery is advanced or trial is near.

Arbaugh: jurisdiction vs. merits

A perennial defense move is to dress up a merits argument as a jurisdictional one. The Supreme Court has repeatedly pushed back. Arbaugh v. Y & H Corp., 546 U.S. 500 (2006), held that the Title VII employee-numerosity requirement was a merits element, not a jurisdictional prerequisite, because Congress had not clearly labeled it as jurisdictional. Id. at 515-16. Arbaugh established a bright-line rule: if Congress has not "clearly state[d]" that a threshold limitation is jurisdictional, courts should treat it as a merits requirement. Id. at 515.

The implications for the response brief are substantial. Where the defendant argues that some element of the plaintiff's claim (a statutory threshold, an exhaustion requirement, a damages floor) deprives the court of subject-matter jurisdiction, the response should check whether Congress actually labeled the requirement jurisdictional. If not, Arbaugh converts the motion from 12(b)(1) into 12(b)(6), with significant practical consequences:

The court accepts the plaintiff's allegations as true on a 12(b)(6) motion (a facial 12(b)(1) motion does too, but factual attacks under 12(b)(1) do not).
A 12(b)(6) dismissal is with prejudice; a 12(b)(1) dismissal is without prejudice and can be refiled in state court.
The merits standard generally lets the plaintiff amend; the jurisdictional standard sometimes does not.

The recharacterization matters even when it does not change the outcome. The response brief should identify the issue and ask the court to apply the correct framework.

Bell v. Hood: jurisdiction over claims that may fail on the merits

The Supreme Court drew a related distinction in Bell v. Hood, 327 U.S. 678 (1946). The Court held that federal-question jurisdiction exists whenever the plaintiff's claim is one "arising under" federal law, even if the claim ultimately fails on the merits. Jurisdiction is lacking only where the federal claim is "wholly insubstantial and frivolous." Id. at 682-83.

Bell v. Hood is the case to cite when the defendant argues that the plaintiff's federal claim is meritless and therefore not within federal jurisdiction. The two questions are separate. A weak federal claim that survives the Bell v. Hood substantiality screen confers federal-question jurisdiction; the court can then dismiss for failure to state a claim on the merits without running afoul of subject-matter limits.

Jurisdictional discovery on factual attacks

Where the defendant has launched a factual attack on jurisdiction (often supported by affidavits about citizenship, amount in controversy, or the existence of an alleged sham defendant), the plaintiff is generally entitled to jurisdictional discovery. The response brief should:

Specifically identify the jurisdictional fact in dispute.
Identify the categories of discovery needed to develop that fact.
Propose a reasonable schedule.

Where the defendant has launched a facial attack, no jurisdictional discovery is available because no extrinsic evidence is being considered. A response brief mistakenly seeking jurisdictional discovery on a pure facial attack invites the court to deny the request and proceed on the pleadings.

How to brief the opposition

A subject-matter-jurisdiction response has a predictable structure.

Introduction

One short paragraph identifying the jurisdictional basis (diversity, federal question, supplemental) and stating why the defendant's motion fails.

Statement of facts

A factual narrative of the jurisdictional facts, with citations to the complaint and any supporting affidavits.

Legal standard

A short section that identifies the relevant jurisdictional statute, the standard for facial versus factual attacks, and the burden of proof.

Argument

Organized by jurisdictional theory.

For diversity: complete diversity, amount in controversy, fraudulent joinder where applicable.
For federal question: the well-pleaded complaint rule, Grable and Gunn if state-law claims are involved.
For supplemental jurisdiction: common nucleus of operative fact, § 1367(c) considerations.
Arbaugh recharacterization if the defendant has dressed up a merits argument as jurisdictional.
Bell v. Hood if the defendant argues that an alleged weak federal claim defeats jurisdiction.

Request for jurisdictional discovery (alternative)

If the motion is a factual attack and the record is incomplete, request limited jurisdictional discovery with a specific proposal.

Conclusion

Ask the court to deny the motion. In the alternative, ask for leave to amend any jurisdictional pleading defect, or for jurisdictional discovery.

Common errors that sink subject-matter responses

Failing to distinguish facial from factual attacks. The standards differ, and so does the available discovery. A response that proceeds as if the attack were facial when it is factual concedes the right to discovery.

Pleading citizenship by residence. Diversity turns on domicile, not residence. A response that pleads "the plaintiff resides in California" rather than "the plaintiff is domiciled in California" leaves a hole the defendant can exploit.

Overreading Grable. Most state-law claims do not satisfy the Grable substantiality requirement after Gunn. A response that asserts Grable jurisdiction without addressing all four factors usually loses.

Letting the defendant convert a merits argument into a jurisdictional one. Arbaugh matters. Check whether the threshold the defendant attacks is genuinely jurisdictional. If not, insist on 12(b)(6) framing.

The bottom line

A subject-matter-jurisdiction response succeeds when the brief: identifies the jurisdictional theory precisely, distinguishes facial from factual attacks, walks the court through the complete-diversity rule or the Grable-Gunn federal-question analysis, and pushes back against defense efforts to relabel merits arguments as jurisdictional under Arbaugh. It fails when the response pleads citizenship loosely, leans on Grable without addressing Gunn, or fails to request jurisdictional discovery on a factual attack.

Subject-matter jurisdiction is the federal court's authority to hear the case. The response brief's job is to put the right authority on the record, with the right factual support, in the right doctrinal framework. Done well, the response either ends the motion at the pleading stage or sets up the limited discovery needed to win on a fuller record.