Substantive rules typically state the rights and duties as among citizens, and disclose the circumstances where courts redress violations of those rights and duties. Procedural laws, on the other hand, are rules of procedure that have been adopted by courts and legislatures, and that instruct persons on how to bring a controversy before a court, and how to proceed in that court to obtain redress. A workable description of procedural rules is that they prescribe the mechanics of litigation.
The substance-procedure distinction comes up in various areas of our law. Choice of law is a good example. Who can forget Erie Railroad Co. v. Tompkins from our first year of law school? In Erie, the U.S. Supreme Court held that where federal court jurisdiction is grounded on diversity of citizenship, the federal court must apply the substantive law of the forum state as the rule of decision, and can apply federal common law only as to matters of procedure. . . .
For more information about Justice Jacobs’s Donahue Lecture (which served as the basis for this article) please click here.