[This is one of a set of posts serializing my law review article on this subject; please see the article for footnotes, and for more details.] To get a sense of why some people worry — and rightly so, I think — about the use of foreign law in American constitutional decisionmaking, consider this passage from Professor Peter J. Spiro’s Treaties, International Law, and Constitutional Rights, 55 Stanford Law Review 1999, 2025-28 (2003) (emphasis added). Professor Spiro is a supporter of the greater use of international law (here, referring to international human rights law) in the American legal system, and here’s what he writes:

“[T]his analysis [supporting the use of international law in American courts] supplies a normative basis for national decisionmakers to rebalance rights. To take the concrete case, an international norm against hate speech would supply a basis for prohibiting it, the First Amendment notwithstanding.

“C. Insinuating International Law

“It is unlikely in the extreme that the treatymakers would undertake such a frontal assault against the supremacy of constitutional rights given the clear current lack of constitutional authorization to constrain rights on international law grounds ….

“The analysis is not, however, irrelevant to current constitutional practice, for it also justifies putting international regimes to work in the context of constitutional interpretation. This use of international regimes has been engaged. In U.S. courts, those asserting rights are no longer embarrassed to deploy international law arguments, as they once were. The United States Supreme Court is regularly subjected to such arguments, especially from amici (including foreign government amici). International law is becoming part of the vocabulary of American constitutional law. Although its doctrinal place remains unsettled, international law appears poised to make unprecedented inroads in the making of American constitutional law [giving Atkins v. Virginia as an example]….

“This battle is now being fully engaged, on academic, judicial, and policy fronts. Deploying international law as an interpretive tool reflects a defensive strategy, ostensibly a process of domestication rather than one of submission. This may mask what is, in fact, a partial displacement of constitutional hegemony. International law may be a process in which the United States and U.S. entities participate, but it is not a creature of the Constitution. On the other hand, resistance and insulation may no longer be viable options. One can expect more frequent deployment of international norms as part of the domestic rights discourse. In the long run, international norms may be played, not merely as persuasive agents, but as trumps.

“Constitutional rights have presented a discursive bulwark against the encroachment of international law. The continuing refusal to contemplate the international determination of rights betrays the embedded nationalist orientation of constitutional theory, and the field of foreign relations law proves to be no exception. These nationalist assumptions may be conceptually vulnerable in the face of the changing architecture of international law and community. Constitutional rights have bowed to the treaty power and the exigencies of foreign relations as a matter of historical practice, even as the inviolability of domestic rights interpretation has been set as a matter of constitutional faith. Accompanying doctrines of constitutional hegemony, deviations notwithstanding, were justified in a world in which law offered no protection of individual rights. As the regime of international human rights grows thick, however, that justification should no longer stand unchallenged. As transnational society develops a common rights culture, one in which the disaggregated United States enjoys a voice, the supremacy of international rights may be normatively sustainable. In the short term, this argues for the relevance of international norms in domestic constitutional interpretation. In the long run, it may point to the Constitution’s more complete subordination.”

Professor Spiro’s reasoning suggests that there is cause to be concerned, I think, about the use of foreign law in defining American constitutional rules. That’s true whether you favor free speech, abortion rights, the right to bear arms, a strong separation of church and state, or the exclusionary rule — all areas in which American constitutional law is more government-constraining in many ways than foreign constitutional law tends to be.

Now there is a longstanding tradition of relying on foreign law in determining the scope of American constitutional law; whatever is going on here is not some sharp break with traditional American practice. See, for instance, Steven G. Calabresi (a cofounder of the Federalist Society) & Stephanie Dotson Zimdahl, The Supreme Court and Foreign Sources of Law: Two Hundred Years of Practice and the Juvenile Death Penalty Decision, 47 Wm. & Mary L. Rev. 743, 752-53 (2005); see also, e.g., United States v. Reynolds, 345 U.S. 1 (1953); Ker v. Illinois, 119 U.S. 436 (1886); Hurtado v. California, 110 U.S. 516 (1884); Knox v. Lee, 79 U.S. (12 Wall.) 457 (1870). And of course courts routinely rely on many sources, including law review articles or professional groups. If the criticism of foreign law is that it wasn’t enacted by American lawmaking processes, we should recognize that the authors of those works likewise weren’t elected or appointed by Americans to make law for Americans.

But foreign law is law, and seemingly an expression of public sentiment in allied and respected countries, not just the views of a few academics or even of a professional association. Judges therefore may well be more likely to view foreign law as having moral authority.

Judges may find the arguments of law professors to be persuasive, and they may find the factual claims of professors who have studied certain fields to be credible. But they will rarely view the opinions of law professors as having significant normative authority, especially in deciding whether to strike down a statute. And recent opinions, especially Roper v. Simmons (involving the death penalty for murderers who committed their crimes before age 18), suggests that the Court viewed international practice as normatively authoritative.

At the same time, even Justice Scalia, who has sharply criticized reliance on foreign law in this context, has concluded that it is proper to use foreign law in some contexts. One example is Schriro v. Summerlin, which dealt with whether certain expansions of the right to a jury trial (expansions that Justice Scalia endorsed) should be applied retroactively on habeas review. Under the Court’s retroactivity jurisprudence, such retroactive application of a procedural rule would be justified only if it is a “‘watershed rule[] of criminal procedure’ implicating the fundamental fairness and accuracy of the criminal proceeding.” And the expansion of the jury trial right, Justice Scalia held (in an opinion joined by the four other conservative Justices), was not such a watershed rule, partly because:

“for every argument why juries are more accurate factfinders, there is another why they are less accurate. The [dissent below] noted several, including juries’ tendency to become confused over legal standards and to be influenced by emotion or philosophical predisposition. Members of this Court have opined that judicial sentencing may yield more consistent results because of judges’ greater experience. Finally, the mixed reception that the right to jury trial has been given in other countries, though irrelevant to the meaning and continued existence of that right under our Constitution, surely makes it implausible that judicial factfinding so ‘seriously diminishe[s]’ accuracy as to produce an ‘impermissibly large risk’ of injustice. When so many presumably reasonable minds continue to disagree over whether juries are better factfinders at all, we cannot confidently say that judicial factfinding seriously diminishes accuracy.”

So even Justice Scalia is sometimes willing to consult foreign law in crafting American legal rules. He reasons that such consultation is improper when determining the “meaning and continued existence” of a constitutional right. But it is just fine, he concludes, when a court is considering other questions, such as the nonconstitutionally mandated rules of habeas corpus.

I tentatively agree with Justice Scalia’s view that it’s not sound to define the meaning of American constitutional rights with reference to foreign views of such rights. At the same time, there is little that state legislatures can do about this. State law cannot directly bind the U.S. Supreme Court in its interpretation of the U.S. Constitution. And while state law might at times indirectly influence the Court, by sending a message that some American institutions disapprove of the use of foreign law, such effects are likely to be slight.

At the same time, as I’ll explain in further posts, excessive rejection of foreign law by state legislatures can cause lots of problems in much more mundane fields — tort lawsuits, everyday business contract disputes, family law adjudication, and more. It would be a mistake for the understandable concern about foreign law in the Supreme Court’s constitutional decisionmaking to lead states to ban the use of foreign law more broadly.