You Are Free to Practice the Invention of An Expired Patent. Or Are You?

Article 1, Section 8, Clause 8 of the U.S. Constitution grants Congress the power “To promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries.” This codified the institution of U.S. patents.

The first U.S. Patent Act was passed into law in 1790. Thomas Jefferson made the first amendment to the Act in 1793. As the pace of patenting increased, so did the need to modify the guidelines. U.S. patent law underwent significant modification in 1952, establishing the modern U.S. patent system. Other amendments have been made to the patent laws, including a number of changes made under the Leahy-Smith America Invents Act of 2011. Nevertheless, one thing has remained constant - the patent bargain between the inventor and the state.

The patent bargain can be viewed as a quid pro quo: the inventor seeks the protection of the law for the invention, and the law says the inventor can enjoy a limited period of exclusivity over the invention, provided the inventor discloses the invention. A U.S. patent gives the holder the right to exclude others from making, using, offering for sale, or selling the invention throughout the U.S. or importing the invention into the U.S., and, if the invention is a process, the right to exclude others from using, offering, or selling in the U.S., or importing into the U.S., products made by that process.[i] The term of a U.S. patent is generally 20 years from the date the application for patent is filed. This principle of exchange has fueled innovation and technological development.

The public has come to understand that when a patent expires, the covered invention enters the public domain, free for anyone to practice. Early Supreme Court decisions established this tenet.

In Evans v. Hettich, the Court stated that one reason for requiring clarity of disclosure in a patent is “to enable the public to enjoy the full benefit of the discovery, when the patentee's monopoly is expired, by having it so described on record that any person skilled in the art of which the invention is a branch may be able to construct it.”[ii] In explaining a party’s right to use the invention of an expired patent, the Court in Coats v. Merrick Thread Co. noted that the “plaintiffs' right to the use of the embossed periphery expired with their patent, and the public had the same right to make use of it as if it had never been patented.”[iii] The Singer Mfg. Co. v. June Mfg. Co. Court  stated: “It is self-evident that, on the expiration of a patent, the monopoly created by it ceases to exist and the right to make the thing formerly covered by the patent becomes public property. It is upon this condition that the patent is granted. It follows as a matter of course that on the termination of the patent, there passes to the public the right to make the machine in the form in which it was constructed during the patent.”[iv]

In United States v. American Bell Tel. Co., the Court addressed Alexander Graham Bell’s telephone patent, stating: “That patent has expired and all the monopoly which attaches to it alone has ceased, and the right to use that invention has become public property.”[v] “No one questions that the Bell patent has expired, and that all of his invention is free to the use of the public.”[vi] The Court in United States v. Dubilier Condenser Corp. expanded the tenet, stating: “An exclusive enjoyment is guaranteed him [patentee] for seventeen years, but, upon the expiration of that period, the knowledge of the invention inures to the people, who are thus enabled without restriction to practice it and profit by its use.”[vii]

A more recent Supreme Court opinion promulgated the tenet, noting: “An unpatentable article, like an article on which the patent has expired, is in the public domain, and may be made and sold by whoever chooses to do so.”[viii] In addressing patents covering rifles, the Court stated that “when such patents expired, anyone 'who has ordinary skill in the rifle-making art' is able to use the technology of such expired patents for which Colt earlier had a monopoly position for 17 years.”[ix] In Bonito Boats, Inc. v. Thunder Craft Boats, Inc., the Court stated that “For almost 100 years it has been well established that in the case of an expired patent, the federal patent laws do create a federal right to ‘copy and to use.’”[x] Less than a decade ago, the Court stated: “And when the patent expires, the patentee’s prerogatives expire too, and the right to make or use the article, free from all restriction, passes to the public.”[xi] Now the Court has once again repeated the tenet that “upon the expiration of [the patent], the knowledge of the invention [i]nures to the people, who are thus enabled without restriction to practice it.”[xii] (emphasis added).

No wonder we have come to equate patent expiration with absolute freedom to use the formerly protected invention. The problem is this tenet is flawed. An expired patent does not necessarily convey a public right to practice the invention “without restriction.”

There may be a legal restriction to practicing the invention of an expired patent, in the form of a dominating patent. The following figure illustrates how a dominating patent can present a legal restriction to practicing the invention of an expired patent. In the figure, the box labeled “Patent A” represents a dominating patent and the box labeled “Patent B” represents an expired patent.

For the purpose of discussion, consider Patent A covers an automobile transmission configured to operate in an automatic shifting mode. Consider expired Patent B covers a dual-mode automobile transmission, configured to operate in a manual shifting mode or an automatic shifting mode, as selected by the driver. In this scenario, we can assume that Patent A was issued before Patent B. Patent B was allowed because the addition of the alternative manual shifting mode met the novelty and non-obviousness standards for patentability.  

Patent A “dominates” Patent B because in every instance where the transmission covered by Patent B operates in the automatic shifting mode, it falls within the scope of Patent A, thereby infringing Patent A. If Patent B expires while Patent A is active, the enforceability of Patent A is not affected (Patent A remains enforceable against all unauthorized practices of its claimed automatic shifting transmission). Anyone who practices the transmission of expired Patent B in the automatic shifting mode without authorization from the holder of active Patent A, infringes Patent A. Therefore, it is incorrect to say that an expired patent (e.g., Patent B) necessarily passes the invention to the public domain to be practiced “without restriction.” A more accurate statement is that an expired patent terminates the period of exclusivity held by the patent owner, but the covered invention may still be subject to an active dominating patent.

Won’t Patent A expire before Patent B, you ask? Not always. Throughout the development of U.S. patent law the term of a patent has been modified and, in some instances, it has been amended to allow for term extensions. Recognizing that FDA approval for new drugs can take years, resulting in a diminished patent term by the time the drug enters the market, Congress passed laws allowing for term extensions for certain drug patents.[xiii] The term of general utility patents can also be extended. Under 35 U.S.C. § 154(b) of the Patent Act, the term of a U.S. patent can be extended if delay in issuance of the patent is attributed to the Patent Office.  

Consider for example, U.S. Patent No. 7,667,562. The application for the ‘562 patent was filed on February 20, 1990. The application underwent examination in the Patent Office for 20 years, with the patent issuing on February 23, 2010. As a result of the protracted examination, the USPTO extended the term of the ‘562 patent by 17 years beyond the normal term. As a result, the ‘562 patent will expire on February 23, 2027 (provided the maintenance fees are paid). In effect, this means that other patents filed after the filing date of the ‘562 patent have already expired, while the ‘562 patent remains as a potentially active dominating patent to the expired patents.    

Note that an active dominating patent covers a subordinate patent both while the subordinate patent is active and after it expires. Returning to the example of Patent A and Patent B above, recall that in every instance where the transmission covered by subordinate Patent B operates in the automatic shifting mode, it falls within the scope of active dominating Patent A, thereby infringing Patent A. Infringement occurs while dominating Patent A remains active, regardless of whether Patent B is expired or active. In reality, cases occur where the invention of a newly issued patent may fall within the scope of an active dominating patent since many newly patented inventions are improvements of prior patented inventions. Thus, while it may seem counterintuitive, the possible existence of dominating patents leads to an understanding that a patent grants the holder the right to exclude others from practicing the claimed invention, but not necessarily the right to practice the invention.

How can the Patent Office issue patents that may be subordinate to dominating patents, you ask? The function of the Patent Office is to grant patents to inventors whose inventions meet the novelty, usefulness, and nonobvious standards set forth by the Patent Act.[xiv] Patent Examiners are not tasked with analyzing patent claims to determine if a patent application is or may be subject to a dominating patent. It is left to the patent holder to police his or her own patent.       

In sum, an expired patent is subject to restriction from practice to the extent the subject invention is within the scope of an active dominating patent. Anyone seeking to practice an invention covered by an expired patent would be well advised to conduct a patent review to determine if there are any dominating patents that may present an infringement issue.

[i]     35 U.S.C. § 154 (2023); See also 35 U.S.C. § 163 (2023).

[ii]     20 U.S. 453, 458 (1822).

[iii]    149 U.S. 562, 572 (1893).

[iv]    163 U.S. 169, 185 (1896).

[v]     167 U.S. 224, 243 (1897).

[vi]    Id. at 249.

[vii]   289 U.S. 178, 186-87 (1933).

[viii]   Sears, Roebuck & Co. v. Stiffel Co., 376 U.S. 225, 231 (1964).

[ix]    Christianson v. Colt Indus., 486 U.S. 800, 805 (1988).

[x]     489 U.S. 141, 165 (1989).

[xi]    Kimble v. Marvel Entertainment, LLC, 576 U.S. 446 (2015).

[xii]   Amgen Inc. v. Sanofi, 598 U.S. _ (2023) (citing United States v. Dubilier Condenser Corp., 289 U.S. 178, 187 (1933)).

[xiii]   Drug Price Competition and Patent Term Restoration Act of 1984, Pub. L. No. 98-417; See also 35 U.S.C. § 156.

[xiv]   35 U.S.C. §§ 101-103 (2023).