Two hundred twenty-nine years ago, the Founders issued a declaration proclaiming their independence from a European power. Today, jurists invoke that document in an effort to make American law at least partially dependent on foreign law, and their argument has in recent months won significant support from the Supreme Court.

In a series of controversial cases over the past few years, the Supreme Court has suggested that what the American Constitution permits and forbids should be determined at least partly by looking at other countries’ laws. This took full bloom in Roper v. Simmons, decided this March: the court held that the Constitution does not permit the execution of 16- and 17-year-old murderers, reversing its own ruling on the same question 16 years ago. Fully 20% of the court’s opinion was devoted to canvassing foreign and international law, and suggesting that America should be guided by it.

The Declaration’s preamble speaks of paying a “decent respect to the opinions of mankind.” Internationalist scholars and judges point to this phrase as evidence that the Founders would have approved of grafting foreign law onto the Constitution. In Roper, at oral argument, Justice Ginsburg asked rhetorically: “did [Thomas Jefferson, author of the Declaration] not also say that to … lead the world, we would have to show a decent respect for the opinions of mankind?” The court’s opinion in that case extols the importance of the “opinion of the world community.” Speaking to the American Society of International Law shortly after the decision, Justice Ginsburg celebrated it as “perhaps the fullest expression to date on the propriety and utility of looking to ‘the opinions of [human]kind.’ “

This appeal to the Declaration perverts its meaning by lifting the relevant passage out of its textual and historical context. The Declaration actually says that “a decent respect to the opinions of mankind requires that they should declare the causes which impel them to the separation.” In other words, America should give reasons for its actions. The Declaration is a public-relations document designed to explain and justify the colonists’ actions. This is the opposite of the spin put on it by internationalist lawyers, who say it shows that we “learn from others.” Rather, the Declaration seeks to teach other nations.

Indeed, the Declaration shows that when there is a difference between international opinion and American opinion, the latter trumps. In 1776, there was no basis in international law for throwing off the rule of a sovereign monarch. Doing so contradicted the dominant opinion of nations, which were themselves monarchies. Had the colonists taken the court’s approach, they would have said, “Well, everyone else is doing taxation without representation, there must be something to it.”

The circumstances under which the Declaration was drafted further contradict its use by the internationalists. Congress decided to officially declare independence as part of an appeal for arms and money from Britain’s enemies. But many in France and Spain thought the colonists were dabblers, fair-weather revolutionaries who would quickly accept some kind of compromise with the crown. That would leave anyone who had lent them guns and funds in the lurch.

The Declaration sought to show that the breach with Britain was irreparable, and that the colonists were committed to the fight for the long haul. Thus the “opinions of mankind” to which it appeals are not opinions about the legality of the colonists’ actions but rather about the likelihood of their success and subsequent ability to repay loans. The “mankind” in question is simply those nations that might provide concrete support to America.

Of course, Jefferson’s words themselves cannot resolve the question of whether judges should look to foreign law. However, the repeated misrepresentation of a basic founding document by justices of the Supreme Court and leading scholars should raise concerns about how accurately they would interpret the more esoteric universe of foreign legal materials with which they seek to arm themselves.

Mr. Kontorovich is visiting professor at the University of Chicago Law School in the 2005–06 academic year, and an assistant professor at George Mason University School of Law.