The Erie Doctrine
A federal court sitting in diversity applies state substantive law and federal procedural law. Everything else in Erie-land is figuring out which side of that line a rule falls on—in the right order.
There is no general federal common law. A diversity court is borrowing the state's claim—so the outcome shouldn't change just because the plaintiff crossed the street to the federal courthouse. That instinct drives every step below.
The hierarchy—work it in order
Federal court, state-law claim
The highest federal authority on point controls.
A federal constitutional provision on point?
Apply it. The Constitution beats everything—e.g., the Seventh Amendment jury right.
A federal statute on point?
Apply the statute (Stewart—§1404 transfer beat state anti-transfer policy).
A Federal Rule on point?
Apply the Rule if valid under the Rules Enabling Act (Hanna)—none has ever been struck down.
Unguided Erie
Substantive → state law. Use the twin aims.
Step by step, with the citations
A Federal Rule that squarely covers the question applies if it's valid under the Rules Enabling Act (28 U.S.C. §2072)—it really regulates procedure and doesn't abridge, enlarge, or modify a substantive right. The fight is usually about coverage, not validity.
Coverage matters: where state law layers on a substantive requirement (a medical-affidavit prerequisite, a damages cap), courts often find the Federal Rules don't answer that question at all—so state law survives alongside the Rule.
Rule 15 decides whether Lana's amended complaint relates back, even if state law is stingier—the Rule is on point and valid. But the state's requirement that malpractice plaintiffs file an expert affidavit first? No Federal Rule covers it; Lana must comply.
The unguided Erie choice
Outcome-determination through the twin aims: would ignoring the state rule (1) encourage forum shopping into federal court, or (2) cause inequitable administration of the laws? Judge it from the front of the case, not hindsight (Guaranty Trust via Hanna's gloss). Then balance the interests—the state's stake in its rule vs. the federal system's in its own practice (Byrd).
- Statutes of limitations + tolling rules
- Choice-of-law rules (Klaxon)
- Elements & defenses of the claim
- Standards for reviewing damages awards (Gasperini)
- Burdens of proof
- Everything a valid Federal Rule covers—pleading, service, discovery, summary judgment
- Judge/jury allocation (Byrd)
- Federal statutes on venue and transfer
- Appealability and court administration
The state's two-year statute of limitations ran on Lana's claim before she filed in federal court. Substantive—the federal court applies it and dismisses. Letting Lana revive a dead claim by picking the federal courthouse is exactly the forum shopping Erie forbids.
Essay recipe: name the sitting (diversity) → march the hierarchy (Constitution? statute? Rule?) → if none, label the state rule substantive or procedural with the twin aims → cite the classic list if it fits. Two sentences per rung scores; skipping rungs doesn't.
Where the points are
The traps examiners actually set.
- Most tested
- Statutes of limitations as substantive; a Federal Rule on point beating contrary state law (Hanna); working the hierarchy in order instead of jumping to “outcome determinative.”
- Classic traps
- Calling everything “outcome determinative” (judge it through the twin aims, ex ante); applying Erie in federal-question cases (diversity doctrine); assuming a Federal Rule is invalid (never happened); forgetting choice-of-law rules follow the forum state (Klaxon).
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