John M. Benassi and Christopher K. Eppich (San Diego, CA)

United States 
Litigation and prosecution after Festo III


The Federal Circuit recently issued a new opinion applying the facts of the Festo case to the Supreme Court’s analysis in Festo II purporting to offer guidance to lower courts for future determinations. This most recent Festo opinion, Festo III, has further affected patent law and changed patent litigation and prosecution strategies.

The facts of Festo are important and fairly straightforward. Festo Corporation sued Shoketsu and SMC Pneumatics for patent infringement of two US patents, the Stoll patent and the Carroll patent. Both patents claim magnetically coupled rodless cylinders. Claims define the boundaries of a patent’s protection. The trial court ruled for Festo applying the doctrine of equivalents. Under the doctrine of equivalents, even though not all the claimed elements are found literally in the accused device, a patent may nonetheless be stretched to cover the accused device if there are insubstantial differences from the patent claims.

On appeal, the Federal Circuit reversed the trial court’s decision implementing a complete bar approach to the doctrine of equivalents (Festo I). The court decided that since the claim had been narrowed during prosecution, no range of equivalents was available under the doctrine of equivalents.

On further appeal to the Supreme Court, the Court in Festo II rejected the complete bar approach of the Federal Circuit. The Court established a presumption that an amendment made by the patentee that narrows the scope of the claim operates to surrender the claimed element or equivalent. Unless the presumption is overcome, the patentee is restricted to the literal scope of the amended claim. However, a patent owner may rebut this presumption and apply the doctrine of equivalents to expand the claim. The patent owner must establish either that the accused equivalent was (i) “unforeseeable at the time of the [amendment]”; (ii) that “the rationale underlying the amendment [bore] no more than a tangential relation to the equivalent in question”; or (iii) for “some other reason…the patentee could not reasonably be expected to have described the insubstantial substitute in question.”

Thus, as shown in the diagram, an original broad claim(4) which was narrowed (1) to avoid prior art (3) can be broadened to cover an accused device (dark line) if the presumption is overcome. In other words, a claim element narrowed from position (4) to position (1) can be broadened to position (2).

fig 1

Rebutting the presumption

But what evidence is needed to overcome the presumption?

The recent Glaxo line of cases illustrates the lower courts’ inconsistency in application of the Supreme Court’s three prong rebuttal analysis. Each case in the Glaxo line consisted of essentially the same facts, involving the same patent, claims, and prosecution history. Each case presented the same arguments in the context of a summary judgment, but each resulted in a different analysis and different results. In Glaxo I, the Eastern District of Virginia found Glaxo’s attempt to rebut the presumption unpersuasive. Although Glaxo’s arguments were not successful in Virginia, the same arguments convinced the court in the Southern District of New York in Glaxo II. In the final Glaxo case, Glaxo III, the Northern District of California agreed with the Eastern District of Virginia and rejected the Glaxo arguments. Let’s see whether Festo III clarified things.

“Foreseeability” overcoming of presumption

The Federal Circuit in Festo III found the presumption may be attacked under the first rebuttal prong through an objective inquiry. A court should ask whether “the alleged equivalent would have been unforeseeable to one of ordinary skill in the art at the time of amendment”. In its determination, a court may consider any evidence including expert testimony commenting on the foreseeability of the equivalent. As a general rule, if the allegedly infringing equivalent represents technology developed after the time of patenting, the equivalent would not be foreseeable. Therefore, older technology is more likely to be foreseeable and precluded.

“Tangentially related” overcoming of presumption

The court in Festo III determined the patentee may overcome the presumption under the second prong only through an objective inquiry into evidence in the prosecution history of the patent. Thus, the patentee may not introduce additional evidence outside the prosecution history to prove the narrowing amendment was not directly related to the alleged equivalent. However, expert testimony may be introduced if the court finds it necessary to interpret the prosecution history. The Federal Court additionally specified that any amendment made during the prosecution of the patent “to avoid prior art that contains the equivalent in question is not tangential; it is central to the allowance of the claim” and will not overcome the presumption.

“Some other reason” overcoming of presumption

Under Festo III, the patentee may rebut the presumption under third prong by demonstrating a reason for being unable to describe the alleged equivalent at the time of the claim amendment. The Federal Circuit tentatively limited these determinations to evidence within the prosecution history. However, the court left this issue open for future cases to determine whether the patentee may present evidence from any source in special circumstances. The court firmly held that the patentee may not overcome the presumption under the third prong if the alleged equivalent is contained in the prior art.

Litigation tips after Festo III

Patent owners have classically benefited from the in terrorem effect that the threat of litigation, in which a jury decides issues of equivalence. As a result of Festo, this effect must once again be considered, although its reach is not nearly as broad as in the pre-Festo days. For example, the patentee may no longer claim that a claim element narrowed during prosecution reaches an equivalent that was foreseeable at the time of the amendment. Thus, the threat of litigation may be reduced, especially in cases where the accused infringer has incorporated a foreseeable equivalent.

Once a patent owner has decided to sue an alleged infringer, Festo must be considered in choosing the patents and the claims to assert. Patent infringement plaintiffs must carefully examine the prosecution histories of patents being considered for litigation. Patents with claims of varying breadth, at least some of which have not been narrowed during prosecution, are ideal. In addition, the patentee should also be prepared to address the “foreseeability” and “tangential equivalent” issues, and generate evidence to support these arguments. But the patentee must remember that now the question is viewed in terms of a legal presumption; any failure to proffer sufficient evidence could lead to an adverse judgment, as a matter of law.

Festo may result in an increased importance of Markman hearings, especially since literal infringement is now even more important. Markman hearings allow judges to decide how the claims at issue will be interpreted long before the trial begins. Because the ruling in Festo may eliminate the application of the doctrine of equivalents for elements that were narrowed during prosecution, these hearings may, therefore, become “Markman-Festo” hearings. Issues of prosecution history estoppel, such as whether a narrowing amendment occurred, the reason underlying the amendment, and whether any estoppel applies to the equivalent in question would then be decided as well. If narrowing amendments were made during prosecution, and it was found that such amendments were not made pursuant to a reason related to the statutory requirements for patentability, the court would rule that the doctrine of equivalents will be available at trial. If the parties know that the doctrine of equivalents will or will not apply prior to trial, they would be more likely to settle without a trial.

Pre-litigation tips

Although the ruling in Festo generally worsens the position of a patent plaintiff, especially when the claim at issue has been amended, there are still some safe harbors. Patent plaintiffs, for example, may still argue for a broad interpretation of the claim elements, although the same amendments that potentially give rise to an estoppel, may also restrict the literal scope of the claims.

In addition, the patent plaintiff must be prepared to present evidence that the accused equivalent was not foreseeable at the time of the amendment. If this fails, the plaintiff patentee may also argue that the rationale underlying the amendment has only a tangential relation to the equivalent at issue.


As was the case under Festo I, to avoid the potential limiting effects of the Supreme Court’s new presumption, the prosecutor must avoid rejections that require narrowing amendments. Therefore, a thorough analysis of the prior art can help the prosecutor carefully draft claims around the prior art to reduce the chance of a rejection that would require a narrowing amendment.

A prosecutor may choose to file two or more applications directed toward common subject matter to prevent the spread of prosecution history estoppel. Each application could then contain claims of varying scope. One application may claim the invention very broadly, but it may also require amendments for allowance. In this case, the remaining applications that are drafted more narrowly may issue and result in a patent with a viable range of equivalents.

Festo II establishes a significant hurdle to the application of the doctrine of equivalents to claim elements that have been subjected to narrowing amendments during prosecution. Therefore, the obvious solution is to file claims that are certain to be allowed without amendment. Unfortunately, an examiner rarely allows an application to issue without at least one rejection. Therefore, additional strategies for claim drafting must be considered.

One approach involves the filing of a number of different independent claims. The independent claims should encompass a scope that ranges from a very broad claim to a claim that is allowable as written. Theoretically, the examiner should then allow a number of the claims that appear near the narrow end of the claim scope, while rejecting many of the broader claims. The prosecutor can then submit arguments against the rejections or later cancel the rejected claims. Therefore, all of the remaining claims would appear without limiting amendments.

Another approach for avoiding prosecution history estoppel is to file narrowly focused claims in the original application. By filing narrow claims at the beginning of the prosecution, the examiner is more likely to allow a claim without requiring a narrowing amendment. Even if some of the claims are rejected, many of the remaining claims should have an improved chance of escaping without limiting amendments.

Patent claims should be filed in multiple formats, such as product claims, product-by-process claims, methods of manufacture, methods of use, and others. By submitting a greater variety of claims at the beginning of the prosecution, the prosecutor increases his or her chances of obtaining a desired claim that has not been amended.

The Festo decision applied estoppel to amended claims, as well as claims that had been added to replace cancelled claims. Some prosecutors have suggested that this indicates a possible reliance on the ability to trace an amendment that has been made when the court determines if estoppel should apply. Therefore, one could file a preliminary amendment to cancel all of the original claims prior to submitting the new claim set. While this method might reduce the traceability of the new amendments, the court could still construe the new claims as a narrowing amendment. The prosecutor should spend the time to get the claims as he or she wants them prior to filing to avoid the chance that the preliminary amendment could trigger prosecution history estoppel.

35 USC §112, paragraph six allows a claim to recite “means” for performing a particular function. While the function is recited in the claim itself, the corresponding “means”, or structures that perform the function are recited in the written description. Therefore, the prosecutor can list a variety of structures in the written description, and the scope of the claims will also include equivalents to the recited structures.

In the past, means-plus-function claims were used with caution because the patentee was limited to the particular structures that were listed in the specification. In light of Festo, however, means-plus-function claims should be considered in applications where the written description can provide for multiple alternative embodiments of a claim element. Where means-plus-function language has been employed, it may be possible to avoid a prior art rejection without amending the actual claim.

In the event that a narrowing amendment must be made, it is still important to obtain the maximum reach of the literal scope of the claims. Thus, the prosecutor should consider increasing the use of terms of approximation, such as “about” or “substantially”, to increase the literal scope of the claims.

Under Festo, even a minor amendment risks leading to the amended limitation being afforded no doctrine of equivalents. The prosecutor should resist the temptation to submit the amendment solely to expedite the examination of the patent. Instead, the prosecutor should make arguments to the examiner without amending. If the examiner persists with the rejection, the prosecutor can pursue additional routes to avoid a limiting amendment.

Festo makes it clear that any amendment relating to a statutory requirement for patentability triggers the potentially preclusive presumption. This includes amendments that are made for “clarity” or “definiteness” to overcome rejections based on 35 USC §112, paragraph two. Therefore, it is important to write clear, well-structured claims in the original application to reduce the necessity for clarifying amendments.

Another method of avoiding prosecution history estoppel is to file new claims instead of amendments. While this method is simply changing the form of the claims, technically, it does not produce an amended claim. This situation often arises when the examiner determines that a dependent claim is allowable except for its dependence on a rejected base claim. In the opinion of many prosecutors, a dependent claim that is rewritten in independent form should not be treated as an amendment that gives rise to prosecution history estoppel. Unfortunately, the application of Festo to this situation is unclear.

Rule 132 declarations provide the prosecutor with a method of presenting evidence to the examiner without filing a narrowing amendment. Declarations can be used to rebut the examiner’s position on a variety issues, such as enablement, definiteness, obviousness and trading of the prior art. Although the declaration may give rise to argument based estoppel, the declaration should avoid Festo and its presumption against the doctrine of equivalents.

The Patent Act provides an appeal procedure when an examiner’s final rejection of a patent claim is based on prior art or material deficiencies in the disclosure. A prosecutor who is dissatisfied with the examiner’s final rejection can appeal the rejection to the Board of Patent Appeals and Interferences. In light of Festo, prosecutors may now choose to appeal a rejection, even if it could be overcome by an amendment. Although the appeal process can be very time consuming, it is an option that prosecutors should consider to avoid narrowing amendments, particularly when a key element or limitation has been rejected.

Interviews with the examiner have long been available and utilised by prosecutors to make headway toward allowance. Following Festo, such interviews may become more useful than ever. Before making any amendment for a reason related to patentability, the prosecutor should call the examiner to identify the absolute minimum response required to get the claim allowed. In addition, the prosecutor should request the examiner to review the amendment prior to filing it. Additional interviews with the examiner may provide a method for reducing unnecessary amendments and arguments that give rise to prosecution history estoppel.