Also known as: substantive laws
Written by attorneys · grounded in primary & secondary sources — see below
The part of the law that creates, defines, and regulates the rights, duties, and powers of parties.
Simone Sanders, a citizen of State A, sues Silverline Industries, a State B corporation, in federal court in State A for breach of a supply contract negotiated and performed in State A. The court applies State A contract rules defining the parties' rights and duties rather than any independent federal standard. Silverline's motion for judgment on the pleadings is evaluated under those state-created obligations.
Selena Singh prevails on a state-law tort claim against Southland Foods in federal court. Because the governing substantive law treats reasonable attorney fees as an element of compensatory damages, the court requires Singh to prove the amount of fees at trial rather than by post-judgment motion. The jury returns a verdict that includes the fee component.
Select any source to read its text and confirm it supports the definition.
Sebastian Santos, a State A resident, sues Sterling Dynamics in federal court in State B over a contract formed in State A. The court first applies State B's choice-of-law rules, which are treated as substantive, to decide that State A law governs the parties' contractual rights and duties. The case then proceeds under those State A rules.
Sarah Sullivan obtains a final federal judgment dismissing a consumer class action against Sentinel Security. Congress later enacts a statute directing courts to reopen all such judgments and recalculate damages under new substantive standards. The court refuses to reopen the case, holding that the statute impermissibly interferes with the final adjudication of the parties' rights.
Santiago Sanchez challenges a state statute restricting reproductive services as violating protected liberty interests. The court analyzes whether the statute infringes substantive rights derived from the Due Process Clause rather than merely questioning the fairness of state procedures. The claim proceeds on the basis of those substantive protections.
Steven Silva alleges that two telecommunications firms entered an agreement to allocate markets. The court examines whether the complaint states a plausible claim under the substantive antitrust rules governing conspiracies rather than merely parallel conduct. The action is dismissed because the pleaded facts fail to show the required substantive violation.
Substantive law creates and defines the rights and duties that determine the outcome of a claim. In diversity actions a federal court must apply the substantive law of the state where it sits, including that state's conflict-of-laws rules. Procedural rules, by contrast, govern the manner of enforcing those rights in federal court.
Supporting sources
Choice-of-law rules are substantive for Erie purposes because they determine which state's body of rights and duties will govern the parties. A federal court sitting in diversity must therefore follow the forum state's conflict rules rather than fashioning its own.
When the substantive law of the claim makes reasonable fees an element of damages, the amount must be established as part of the plaintiff's case at trial. Federal Rule of Civil Procedure 54(d)(2)(A) therefore directs that such fees be proved at trial instead of by post-judgment motion.
Congress may alter substantive rules for cases that have not yet reached final judgment. Once a final judgment has been entered, however, a statute directing courts to reopen the case and apply new substantive standards violates separation of powers.
…U. S. 518, 535. If the opinion commits this Court to the position that the Congress is without power to declare what rules of substantive law shall govern the federal courts, that conclusion also seems questionable. The line between procedural and substantive law is hazy but no one doubts federal power over procedure. Wayman v.…