Berk

Majority — Barrett

Joined by: Roberts, Thomas, Alito, Sotomayor, Kagan, Gorsuch, Kavanaugh

The majority held that when a valid Federal Rule of Civil Procedure directly answers the question at issue, it displaces contrary state law — even state law that might otherwise be considered "substantive" under the Erie doctrine (the principle that federal courts hearing state-law claims must apply state substantive law). The Court reasoned that Rule 8 answers the precise question here: what information must a plaintiff provide about the merits of a claim at the start of a lawsuit. Rule 8 requires only "a short and plain statement of the claim," which implicitly but clearly means that evidence — such as an expert affidavit — cannot also be required. Rule 12 reinforces this by providing only one merits-based ground for dismissal (failure to state a claim) and barring courts from considering materials outside the pleadings when ruling on such motions. The majority also rejected the defendants' argument that Rule 11's reference to affidavits creates a loophole, explaining that Rule 11 only addresses affidavits from the attorney or party themselves, not from third-party experts. Finally, the Court confirmed that Rule 8 is valid under the Rules Enabling Act because it regulates procedure — the manner of enforcing rights — not the rights themselves.

Dissent reasoning

Justice Jackson agreed with the outcome but wrote separately to argue that the conflict is with Federal Rules 3 and 12, not Rule 8. She reasoned that Delaware's law most directly answers the question of what is required to *start* a lawsuit — and Rule 3 already answers that question by stating that a civil action "is commenced by filing a complaint," full stop. Because Rule 3 leaves no room for an additional filing requirement like an affidavit, Delaware's law cannot apply in federal court on that basis alone. Justice Jackson also argued that the majority's reading of Rule 8 is too broad: Rule 8 governs only what a "pleading" must contain, and the affidavit of merit is not a pleading — the majority itself admits this. Stretching Rule 8 to cover documents that accompany (but are separate from) the complaint, she wrote, distorts the Rule beyond its plain meaning. She further argued that the majority's Rule 8 and Rule 12 analyses are logically inconsistent: the affidavit cannot simultaneously be a "matter outside the pleadings" (triggering a Rule 12 conflict) and part of what the pleadings must contain (triggering a Rule 8 conflict).