U.S. Supreme Court Upholds Key Patent Law Doctrine

1997 – Article
Published by Washington Legal Foundation in Legal Backgrounder, Volume 12, Number 9, April 4, 1997


by Gerald J. Mossinghoff *

In a decidedly pro-patent, pro-innovation ruling on March 3, 1997, a unanimous Supreme Court in Warner-Jenkinson v. Hilton Davis ("Hilton Davis") upheld the patent law doctrine of equivalents. Speaking for the Court, Justice Clarence Thomas declined, as he phrased it, to "speak the death" of that important doctrine. The doctrine of equivalents was first defined in the mid nineteenth century, but was made the subject of considerable confusion by a sharply divided twelve-judge en banc Court of Appeals for the Federal Circuit in the Hilton Davis case, with four of the five dissenting judges calling for its abolishment.

Basically, the doctrine of equivalents holds that an inventor can recover from an alleged infringer of his or her patent even though the patent claims -- the legal definition of the invention in the patent -- are not literally infringed by the accused product or process. Nearly fifty years ago, in Graver Tank v. Linde Air Products, a divided Supreme Court blessed the doctrine of equivalents, but in terms that have led to considerable confusion, including the charge that the application -- or some would say misapplication -- of the Graver Tank holding violated the cardinal principle of patent law that a patent should define or claim an invention in such a way as to put would-be infringers on public notice of its metes and bounds.

In speaking for the unanimous Supreme Court, Justice Thomas defined with some precision the basic framework of the doctrine of equivalents, broke new legal ground in its application, and left for a later decision the question of whether the final determination in applying the doctrine of equivalents in any specific case is for the judge or for the jury.

The Doctrine of Equivalents is Alive and Well

The four dissenters from the Court of Appeals for the Federal Circuit in the Hilton Davis case and, of course, the defendant, Warner-Jenkinson, argued that the doctrine of equivalents is inconsistent with the patent statute that requires an inventor to "particularly point out and distinctly claim" the invention in the patent. They argued that the 1950 Graver Tank ruling was overruled by the 1952 Patent Act, now in force. Justice Thomas rejected that position, noting that those arguments were also rejected in the Graver Tank decision under an 1870 statute that was virtually identical to the 1952 Act, and that, in 1952, Congress could easily have overruled Graver Tank, "but did not." He went on to observe that:

Congress can legislate the doctrine of equivalents out of existence any time it chooses. The various policy arguments now made by both sides are thus best addressed to Congress, not this Court.

The Court, however, did . . .

share the concern of the dissenters below that the doctrine of equivalents, as it has come to be applied since Graver Tank, has taken on a life of its own, unbounded by the patent claims.

To address that concern, the Court adopted the position of the late Judge Nies of the Federal Circuit in her dissent in the case. Specifically, the Supreme Court held that:

Each element contained in a patent claim is deemed material to defining the scope of the patented invention, and thus the doctrine of equivalents must be applied to individual elements of the claim, not to the invention as a whole. It is important to ensure that the application of the doctrine, even as to an individual element, is not allowed such broad play as to effectively eliminate that element in its entirety. So long as the doctrine of equivalents does not encroach beyond the limits just described . . . we are confident that the doctrine will not vitiate the central functions of the patent claims themselves.

Prosecution History Estoppel

Since it was first formulated, the doctrine of equivalents has been balanced against what is referred to as "file wrapper estoppel" or "prosecution history estoppel." If, during the prosecution of a patent application in the Patent Office, the inventor had to narrow his or her claims to avoid "prior art" or earlier work by others, the inventor would not be able thereafter to broaden the claim through the doctrine of equivalents in effect to recapture ground already given up. It was on this point that the Supreme Court reversed the Federal Circuit and remanded the case. In the process, the Supreme Court established a new rule.

The Hilton Davis case turned on the question of whether in a process for the ultrafiltration of dyes, an infringing process that used an acidity or "pH" of 5.0 infringed Hilton Davis' claims which specified that the pH should range "from approximately 6.0 to 9.0." That latter range limitation had been added by Hilton Davis during the prosecution of the patent at issue, and it was clear that the upper limit of 9.0 pH was added to avoid prior art. The reasons for inserting the lower limit of the range was not clear from the record before the Supreme Court, and, on that ground, the Court reversed and remanded the case to determine the reasons. Significantly, in remanding the case the Supreme Court announced a new rule of patent law in the following terms:

We are left with the problem, however, of what to do in a case like the one at bar, where the record seems not to reveal the reason for including the lower pH limit of 6.0. In our view, holding that certain reasons for a claim amendment may avoid the application of prosecution history estoppel is not tantamount to holding that the absence of a reason for an amendment may similarly avoid such an estoppel. Mindful that claims do indeed serve both a definitional and a notice function, we think the better rule is to place the burden on the patent holder to establish the reason for an amendment required during patent prosecution. The court then would decide whether that reason is sufficient to overcome prosecution history estoppel as a bar to application of the doctrine of equivalents to the element added by that amendment. Where no explanation is established, however, the court should presume that the PTO had a substantial reason related to patentability for including the limiting element added by amendment. In those circumstances, prosecution history estoppel would bar the application of the doctrine of equivalents as to that element.

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Applied in this fashion, prosecution history estoppel places reasonable limits on the doctrine of equivalents, and further insulates the doctrine from any feared conflict with the Patent Act.

In her concurring opinion, in which Justice Kennedy joined, Justice Ginsburg aded a "cautionary note" on this rebuttal presumption the Court formulated and urged the Federal Circuit to take the following point into consideration on remand:

The new presumption, if applied woodenly, might in some instances unfairly discount the expectations of a patentee who had no notice at the time of patent prosecution that such a presumption would apply.

The Intent of the Infringer Plays No Role

Putting an end to a discussion of intent-based elements of the doctrine of equivalents -- whether the substitution of an equivalent element was the result of copying, designing around a patent, or independent experimentation -- Justice Thomas was very clear:

The better view, and the one consistent with Graver Tank's predecessors and the objective approach to infringement, is that intent plays no role in the application of the doctrine of equivalents.

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Application of the doctrine of equivalents, therefore, is akin to determining literal infringement, and neither requires proof of intent.

The Time for Determining Equivalency Is at the Time of Infringement

Clearing up confusion on the proper time frame to determine whether an element in the accused product or process is equivalent to an element in a patent claim, Justice Thomas again was unambiguous:

Insofar as the question under the doctrine of equivalents is whether an accused element is equivalent to a claimed element, the proper time for evaluating equivalency -- and thus knowledge of interchangeability between elements -- is at the time of infringement, not at the time the patent was issued.

Given the ever-increasing pace of technological development -- for example, the rapid substitution of transistors for vacuum tubes in the late 1950s or the substitution of digital computers for analog computers in the 1960s -- this ruling is quite appropriate.

The invention of the transistor provides a classic example of why the doctrine of equivalents makes so much sense. Before the invention and widespread use of transistors in the 1950s, electronic inventions invariably involved vacuum tubes having anodes, cathodes, and grids. Frequently, patent claims would define the invention using these terms. After their introduction, fully equivalent transistors had collectors, emitters, and bases. By merely substituting a transistor for a vacuum tube in a novel patented circuit, an infringer should not have been able to escape liability under a patent on the circuit. Also, in such a case, the equivalency could only be determined at the time of the infringement and not at the time the patent was granted before there was such a thing as a transistor.

Unresolved Issues

In the line of decisions prior to Hilton Davis that discussed the doctrine of equivalents, a dichotomy evolved in the terminology used to apply the doctrine. Some applied a so-called "function-way-result" test, i.e., "focusing on the function served by a particular claim element, the way that element serves that function, and the result thus obtained by that element." Others preferred an approach that looked to whether or not there were "insubstantial differences" between the invention claimed and the accused product or process. The Supreme Court noted that "different linguistic frameworks may be more suitable to different cases, depending on their particular facts" and that the Court sees "no purpose in going further in micro-managing the Federal Circuit's particular word-choice for analyzing equivalents."

On the question of whether application of the doctrine of equivalents is a task for the judge or for the jury, the Supreme Court noted that although the Federal Circuit held that it was for the jury to decide whether the accused process was equivalent to the claimed process in Hilton Davis -- a proposition for which the Court said there was "ample support in our prior cases" -- the Court went on to indicate that this is "not a question we need to decide today."


Prior to the Supreme Court's decision in Hilton Davis, it is an understatement to say there was considerable confusion surrounding the application of the doctrine of equivalents. That doctrine was first formulated more than a century ago to make sure that inventors -- the creators of new technology -- were amply rewarded for their contributions to society. The confusion surrounding the doctrine clearly had the effect of discouraging investment in research and development. In its remarkably lucid decision, the Supreme Court, by clearing up most of the major issues surrounding the application of the doctrine, has come forth with a very pro-inventor, pro-technology ruling which will serve inventors and society very well into the twenty-first century.

Reprinted with permission. Previously published by Washington Legal Foundation in Legal Backgrounder, Volume 12, Number 9, April 4, 1997.

*.Gerald J. Mossinghoff is Senior Counsel to the Arlington, Virginia law firm of Oblon, Spivak, McClelland, Maier & Neustadt. A former Assistant Secretary of Commerce and Commissioner of Patents and Trademarks in the Reagan Administration, Mr. Mossinghoff is currently a Visiting Professor of Intellectual Property Law at the George Washington University School of Law.