THESE ARE GOOD TIMES for Stephen Breyer. For most of his 21 years as a Supreme Court associate justice, he has been on the losing end of many of the biggest cases. But beginning with the Court’s 5-4 decision upholding Obamacare in 2012, Breyer has won more than he has lost in the cases that matter most. In the last two years, he has generated his two greatest judicial opinions, and rarely in history has a justice made his most notable contributions this late in his time on the bench. After years of merely reacting to and counterpunching against an intellectual agenda defined largely by the Court’s conservatives, led by Antonin Scalia and Clarence Thomas, Breyer has begun to shape an ambitious affirmative reform agenda of his own. And now, he has penned perhaps his best book, The Court and the World.

It is really four books in one. Each minibook is good, and one of the four — on justices as diplomats of sorts — is particularly provocative.

But before we get to the four minibooks, some general background and disclosure. I first met Stephen Breyer on the page, learning Administrative Law in 1982 from an outstanding casebook he had co-edited several years before as a Harvard Law School professor. The book wowed me, and the following year I applied to be his law clerk. (By that point, he had been named to a federal appellate court in Boston, while continuing to teach part time at Harvard — the man has always had tremendous energy.) When he offered me the job, I accepted immediately and enthusiastically. (There was only one other judge at the top of my wish list — a smart young appellate judge on the opposite coast named Anthony Kennedy.) Working for Breyer in 1984–85 was a wonderful experience. The judge was a remarkably generous boss, fun to talk to, filled with ideas, and amazingly quick on his feet. Discussing law with him was like playing lightning chess with a grandmaster. He helped me land my dream job in the legal academy and has remained a friend ever since. I admire him tremendously, and have sent many of my best students to clerk for him. We former clerks enjoy swapping stories about him, and while we sometimes poke fun at his quirks and foibles, our tales are always told with affection. No one who knows Stephen Breyer well has ever spoken ill of him. He is a mensch.

But that has never stopped me from critiquing his opinions — sometimes harshly — both to his face and in print. One of the things that I most admire about him is that he welcomes constructive criticism.

In that spirit, I must confess that until recently I am not sure that I could name a toweringly great Breyer opinion, an opinion for the ages. One reason is that he was often on the losing side, with few chances to speak for the Court in marquee cases. Long ago, when I complimented him on one particularly fine dissent that he had authored, he said nothing, but flashed a sad smile and held up four fingers. The game was to count to five, and in that case he had fallen one vote and one finger short.

But now things are looking up. Two terms ago, he penned his masterpiece in a case involving both administrative law, his first love, and constitutional law, the Court’s main focus. The case, Noel Canning, implicated first principles of both substance and method. Never before had the Court issued a major ruling on the constitutional clause at issue — a clause concerning the president’s power to make certain appointments unilaterally when the Senate is in recess. The case also pitted narrow literalism, championed by Justice Scalia (himself an Admin Law maven and former law prof) against Breyer’s preferred interpretive method, emphasizing broader constitutional purpose and common sense, and reflecting deep respect for how the political branches of government have in fact operated and glossed the constitutional text over the centuries. Breyer’s victory in Noel Canning was all the sweeter because Scalia had raised the stakes, doubling down with a fierce rebuttal. But this time — at last! — Breyer could raise a full five-fingered fist in triumph, backed as he was by his fellow liberals (Justices Ruth Bader Ginsburg, Sonia Sotomayor, and Elena Kagan) and also, critically, by swing Justice Anthony Kennedy.

If Noel Canning was Breyer’s greatest triumph, another huge success quickly followed, in last term’s Obamacare II case, captioned King v. Burwell. The case involved nice issues of statutory construction and administrative law — Breyer’s wheelhouse. (In addition to being an Admin Law expert, he is a former congressional staff attorney.) And the Court’s opinion — this time 6-3 — was classic Breyer, closely attentive to the overall structure of the statute, deeply respectful of Congress’s main purpose, and impressively policy-wonkish in its grasp of this complicated enactment. And here’s the kicker: not only did this classic Breyeresque opinion win the votes of Chief Justice John Roberts and swing Justice Anthony Kennedy, but Roberts himself wrote the opinion! Breyer has now gotten inside Roberts’s head — the true measure of genuine intellectual influence — and in effect he got the Chief to write the very opinion he himself would have written. Once again, Justice Scalia was relegated to a dissent, gnashing his teeth and rending his toga in obvious frustration at being outmaneuvered.

Which brings us to Breyer’s latest book, which is also aimed, albeit subtly, at Scalia. In 1997, Breyer and Scalia famously clashed, in a federalism case called Printz, about whether and how foreign constitutional law might be useful in interpreting the US Constitution. Breyer was on the losing end of that case; and in his new book, he generally purports to detour around this delicate subject. Instead he focuses on the role of foreign and international law: (1) in deciding national-security issues (which often involve persons and events beyond US shores); (2) in pondering whether various ambiguous American statutes are best read to regulate conduct outside the US; and (3) in construing federal treaties, which by their very nature implicate foreign governments — a.k.a. treaty partners. In all three contexts — in each of these three minibooks — Breyer skillfully shows that American courts must think carefully about foreign and international legal materials.

The indispensable role of foreign and international law in the context of extraterritorial statutes and treaties is almost self-evident; Breyer’s main contribution here is to show in nice detail how non-American legal elements have interacted with American law in a wide range of actual Supreme Court cases, many of them cases in which he himself participated. The role of foreign and international law in domestic national-security cases is less self-evident, and here, Breyer makes a particularly nice move by highlighting the fact that the rights revolution in American case law — the Warren Court — roughly coincided with the 1948 Universal Declaration of Human Rights, the 1959 birth of the Human Rights Court in Strasbourg, and the emergence of strong constitutional courts in many advanced democracies outside the US.

Left largely unstated is Breyer’s apparent premise that as American judges become more familiar with non-American legal sources in these three areas, these very same American jurists will naturally begin to think globally and to ponder foreign legal materials even in plain-vanilla cases of American constitutional law that do not directly involve foreign events or foreign persons —that is, in cases such as Printz.

Consider, for example, the death penalty. If state X wants to impose capital punishment on a certain kind of state resident — say a youthful offender or a low-IQ offender or an offender who did not himself pull the trigger — American courts do consider how many of state X’s sister states would allow capital punishment in similar situations. But should American courts also consider the punishment practices of other civilized countries in deciding whether the death penalty in the American case at hand would be impermissibly cruel and unusual? In recent cases, the Court has indeed at times considered foreign-law practices, much to the delight of Justice Breyer and the disgust of Justice Scalia. Last term, Breyer wrote a separate opinion in a case called Glossip, raising the stakes dramatically by suggesting that perhaps all death penalties in America should be deemed unconstitutional. One fact favoring Breyer’s new drift toward abolitionism is that many of the world’s leading democracies have entirely abolished capital punishment within their own societies.

Breyer also uses his new book to subtly challenge Scalia on general interpretive method. The US Constitution does not itself contain a detailed set of instructions about whether it should be read literalistically à la Scalia or with greater attention to spirit and purpose à la Breyer. Nor do most congressional statutes specify just how much judges should emphasize context and general legislative purpose, or whether legislative history (Scalia’s bête noir) should count for much.  But in treaty law — the subject of Breyer’s third minibook — there does exist a treaty that explicitly prescribes general rules for treaty interpretation. And this treaty on treaties — the Vienna Convention on the Law of Treaties — emphatically sides with Breyer against Scalia. It explicitly highlights the importance of a given treaty’s overall “context in light of its object and purpose.” It finds relevant “subsequent practice” above and beyond original intent. (This was a big theme of Breyer’s in the non-treaty case of Noel Canning.) It expressly authorizes judges to consult key pieces of legislative history. To repeat, this treaty only governs treaty interpretation.  But once American judges become increasingly comfortable with this sort of interpretive process in treaty cases, Breyer apparently believes (though he does not quite say, explicitly), that similar interpretive habits will carry over into plain vanilla cases of statutory and constitutional interpretation.

Perhaps the most interesting section of The Court and The World is its fourth and final minibook, “The Judge as Diplomat.” If American judges increasingly engage foreign law and foreign judges, these judges in turn, Breyer argues, will likely pay more attention to American law, and thus America’s soft power and influence will increase. On this view, diplomacy is not limited to presidents, ambassadors, and senators. Federal judges can also play their part in burnishing America’s influence abroad.

It is an interesting argument, and also classic Breyer. He is a conversationalist par excellence and an extremely collegial jurist. He worked hard to befriend Sandra Day O’Connor in his early years on the Court, and now, perhaps, he is at last beginning to forge a bond with Chief Justice Roberts. Thus, with Breyer’s fourth minibook he is once again bringing his ideas about domestic adjudication to bear on international and foreign-law matters. (Here, too, Justice Scalia is the anti-Breyer. Although Scalia can be utterly charming when he wants to be, at times he can be and has been — there is no nice way of saying this — a jerk. He alienated O’Connor at the same time Breyer wooed her. He has attacked Kennedy with special ferocity in a wide range of cases.)

But if Breyer is brilliant in pondering the possible significance of French law and Swiss law and English law and the law of many other modern democracies, he is less good at mastering the full constitutional history of America itself. They say the past is a foreign country. But this is a country that Breyer has not visited enough. He knows far less about the Founding and the Reconstruction than he should — and this is all the more unfortunate because there is a great deal of historical American material that in fact supports many of his best ideas. Good as it is, Breyer’s latest book stumbles in its account of both the Civil War and the Revolution. (On the Civil War, he is too kind to Taney and too ungenerous to Lincoln; and as for the Revolutionary War, he conflates the 1783 Treaty of Paris with the very different 1814 Treaty of Ghent — a small slip in itself, but one that reflects his larger lack of mastery of American constitutional history.)

True, the past cannot be cajoled and befriended and charmed in the same way that Breyer can work his personal magic on his fellow justices or on foreign judges. Studying the past is less fun, perhaps, than seeing the sights in London and Paris. But to reach the next level of greatness, Stephen Breyer needs to visit the Founding and the Reconstruction.

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Akhil Reed Amar is an American legal scholar, an expert on constitutional law and criminal procedure.