Legal monism is the view that necessarily one, and only one, legal system exists. The legal norms of all past, present, and possible communities exist only within in an overarching legal system, which does not itself depend upon any community for its existence. Current legal philosophers — including those who might be described as natural law theorists — reject legal monism. They are legal pluralists, who believe that a multiplicity of discrete legal systems is possible (indeed actual).
Although philosophers of law are pluralists, it is difficult to determine jurists’ views on the matter, for monism and pluralism are both compatible with most judgments that they make. Only in a few narrow areas do monistic and pluralistic judgments about the law diverge. One such area is the conflict of laws (or, as those outside the United States would call it, private international law) — in particular, judgments concerning what I will call rules of authorization, which distribute lawmaking power among the officials of various jurisdictions. Rules of authorization include rules determining when a court has personal jurisdiction and when a legislature has legislative jurisdiction — the power to extend its laws to a matter.
In this essay, I argue that a commitment to legal monism is evident in American jurists’ views on rules of authorization in the nineteenth and early twentieth centuries. I offer as examples Justice Story, Joseph Henry Beale, and Justice Field. What is more, the subsequent choice-of-law revolution did not reject monism. What it rejected was a conception of rules of legislative jurisdiction as dividing lawmaking power into exclusive spheres. Such rules were now understood as giving the lawmakers of a number of jurisdictions concurrent lawmaking power. Whether these rules were understood monistically or not was left open. Indeed, it is possible that current jurists, if forced to take a stand between a monistic and a pluralistic understanding of rules of authorization, would choose monism.
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