Richard Posner’s towering influence on modern legal thought was the focus of the Law School’s recent Chicago’s Best Ideas lecture, which typically features one professor presenting a single novel legal idea. This special edition, however, was part of a daylong celebration on April 23 marking the installation of the first Richard A. Posner Professorship of Law in the Wallman Society of Fellows—to which Professor Thomas J. Miles has been named.  

“We decided to have four faculty members, all former clerks for Dick, each present one of his ideas—because obviously he has four times as many as everyone else,” Dean Adam Chilton said, opening the lunchtime program, “Chicago's Best Ideas — Dick Posner's Greatest Hits.”

For decades, Posner, a legendary jurist and field-defining scholar, reshaped how lawyers, judges, and academics think about the law, bringing economic reasoning, skepticism of formalism, and an insistence on considering real-world consequences to the center of legal analysis. Honoring his extraordinary impact, the four Law School faculty members—Professors Randal C. Picker, Jonathan Masur, Jennifer Nou, and Jacob Goldin—each reflected on a different dimension of his intellectual legacy.

Posner Before Chicago

Picker, the James Parker Hall Distinguished Service Professor of Law, opened with a look at Posner’s early career and the intellectual path that brought him to UChicago. Tracing Posner’s work from his clerkship with US Supreme Court Justice William Brennan through his time in the Solicitor General’s Office and academia, Picker emphasized both the breadth of Posner’s influence and a defining personal trait: intellectual openness.

“He thought he could learn ideas from anyone,” Picker said of Posner, recalling his own experience clerking for the judge. “You have to be focused on each moment as a learning moment—and not be certain where that’s going to come from.”

That openness extended to Posner’s own views. Picker noted that Posner later reconsidered positions he had once defended in major antitrust cases, underscoring a willingness to revise his thinking in light of new arguments and evidence. At the same time, Posner was already engaging deeply with ideas associated with the Chicago School of economics before formally joining the Law School—working with and learning from towering figures like Aaron Director and George Stigler.

“Chicago is a people as well as a place,” Picker said, suggesting that Posner found the intellectual community that would shape his work even before he arrived.

Posner on IP

Masur, the John P. Wilson Professor of Law and David and Celia Hilliard Research Scholar, turned to intellectual property, focusing on Posner’s role in transforming trademark law through an economic lens. Before the rise of law and economics, Masur explained, trademark law was often grounded in moral intuition, centered on the idea that no one should pass off their goods as those of another.

Posner, working with collaborators including legendary UChicago Law Professor William Landes, reframed the field. Trademarks, in this view, serve crucial economic functions: they incentivize producers to maintain quality and help consumers reduce search costs by identifying trusted products.

“The point of a trademark is for consumers to be able to find the product or service that they want,” Masur said.

That framework also clarified the limits of trademark protection. Posner’s analysis helped explain why certain marks, such as “fanciful” or “arbitrary” terms, receive strong protection, while others that are more descriptive must remain available to competitors. It also shaped doctrines like functionality, which prevents firms from using trademark law to control product features that others need to compete.

Masur also highlighted Posner’s distinctive judicial voice, noting opinions that blended economic reasoning with references ranging from the classical architecture of Corinthian columns to the hood ornamentation of early automobiles. “Not a lot of judges write that way,” he said.

Posner on Administrative Law

Nou, the Ruth Wyatt Rosenson Professor of Law, focused on administrative law, demonstrating Posner’s pragmatic approach through a case involving federal regulation of animal enclosures. The dispute turned on whether a government agency’s decision to require eight-foot fences, rather than six-foot ones, was merely an interpretation of an existing rule or a new rule requiring a more rigorous process.

Rather than relying on formal doctrinal tests, Posner emphasized purpose and consequences. When agencies make choices among policy alternatives, he  explained, they are acting akin to legislatures—and must use procedures that allow for public input.

“The task is not to plumb the mysteries of legal theory,” Posner wrote in the case, “but rather to look at the purpose of the distinction” between legislative and nonlegislative rules.

For Nou, the case reflects Posner’s broader critique of administrative law: that courts too often focus on abstract categories instead of the real-world effects of their decisions. That critique remains relevant, she suggested, as contemporary debates increasingly turn toward more formalist approaches.

Posner on Tax Law

Goldin, the Richard M. Lipton Professor of Tax Law, closed the program with a discussion of Posner’s influence in tax law, focusing on a case involving the definition of “reasonable compensation.” There, Posner criticized the use of multi-factor tests that offer little guidance on how to weigh competing considerations, producing outcomes that are unpredictable and disconnected from statutory purpose.

Instead, Posner proposed a more coherent standard tied to economic reality—asking whether an independent investor would view a company’s compensation practices as reasonable given its performance.

“The key,” Goldin said, “is identifying the purpose of the statute and reasoning from that.”

The Common Thread

The discussion concluded with a question posed by Tom Ginsburg, the Leo Spitz Distinguished Service Professor of International Law and Ludwig and Hilde Wolf Research Scholar. Ginsburg asked the panelists whether they saw a common intellectual style running across Posner’s wide-ranging work.

Picker described Posner as “fearless” in stripping problems down to their essentials. Nou pointed to the clarity of his writing. Masur said Posner, like Seventh Circuit Judges Frank Easterbrook, ’73 and Diane Wood, understood that the power of judicial opinions is not just to resolve cases, but to shape entire fields of law.