Real-World Prior Art

67 Pages Posted: 31 Jan 2023 Last revised: 13 May 2024

See all articles by Jonathan S. Masur

Jonathan S. Masur

University of Chicago - Law School

Lisa Larrimore Ouellette

Stanford Law School

Date Written: January 27, 2023


The most fundamental requirement of patent law is that a patented invention must be new. Given the longstanding, foundational nature of this novelty requirement, one might expect its contours to be well settled. And yet some of its most basic aspects remain unresolved. At the center of these unresolved issues lie what we term “real-world prior art.”

In patent law, prior art is something that predates an invention and may render it not new. “Real-world” prior art activities involve using or selling embodiments of the invention. Consider a few examples. Suppose Aleida demonstrates her invention to members of the public but does not allow them to touch it. Has she put the invention into “public use,” thus preventing others from obtaining a patent? Suppose Aleida keeps her invention secret but uses it to provide a commercial service. Has she put the invention into public use, or placed it “on sale”? Or suppose Aleida offers her invention for sale to Charlise, who declines to purchase it. It is black-letter patent law that after one year passes, Aleida cannot patent this invention. But imagine that Bruno independently develops the same invention—can he obtain a patent? These questions are not outlandish law school hypotheticals—they are central issues surrounding whether an invention is or is not novel. Yet litigation over these issues has resulted in conflicting outcomes and contradictory explanations, leaving lower courts and the Patent Office to flounder in applying these doctrines.

In this article, we sort through this conceptual confusion and propose both doctrinal and institutional changes to elucidate this area of law. And we argue that the value of resolving these questions runs much deeper than determining the answer to particular cases. The answers to these questions depend upon—and reveal—the conceptual superstructure of patent law. They implicate patent law’s most central questions: What does it mean for an invention to be new and thus patentable? What policy interests does patent law attempt to achieve, and whose interests does it aim to protect? And what are the conditions under which a party has forfeited the opportunity to obtain a patent? By addressing these issues, we endeavor to place the entire jurisprudence of patent novelty on more solid footing.

Keywords: patent, novelty, prior art, on sale, public use, USPTO, Federal Circuit

JEL Classification: K00, O34, O38

Suggested Citation

Masur, Jonathan S. and Ouellette, Lisa Larrimore, Real-World Prior Art (January 27, 2023). Stanford Law Review, Vol. 76, p. 703 (2024), University of Chicago Coase-Sandor Institute for Law & Economics Research Paper No. 973, U of Chicago, Public Law Working Paper No. 821, Available at SSRN: or

Jonathan S. Masur

University of Chicago - Law School ( email )

1111 E. 60th St.
Chicago, IL 60637
United States
773.702.5188 (Phone)


Lisa Larrimore Ouellette (Contact Author)

Stanford Law School ( email )

559 Nathan Abbott Way
Stanford, CA 94305
United States


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