The theory of the doctrine of equivalents is that an applicant through the doctrine of equivalents should only be able to protect the scope of his invention, Wilson Sporting Goods Co. v. David Geoffrey & Assocs., 904 F.2d 677, 684 (Fed. Cir. 1990), not to expand the protectable scope of the claimed invention to cover a new and unclaimed invention.

In getting what became 4,354,125, the claims (and application) went through amendment after initial rejection over the prior art.

Essentially, '125 claims a motor that takes special advantage of magnetic coupling by having a "small gap" between parts.

Festo sued SMC for infringing '125 in August 1988. SMC eluded literal infringement, so Festo argued infringement under the doctrine of equivalents, and initially won.

Appeals followed. At first, the CAFC wanted the bar to DOE to be "complete" given relevant claim amendment, but the Supreme Court found three exceptions to bar by prosecution estoppel: (1) the the equivalent was “unforeseeable at the time of the application,” (2) the amendment was no more than tangential to the equivalent in question, or (3) “some other reason suggest[s] that the patentee could not reasonably be expected to have described the insubstantial substitute in question.” The CAFC then framed the issue as being a question of law, not fact-based, and thus within judicial province.

After an initial panel decision affirming the judgment, Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 72 F.3d 857 (Fed. Cir. 1995) (“Festo II”), the Supreme Court granted certiorari and remanded for consideration of the prosecution history estoppel question in light of Warner-Jenkinson Co. v. Hilton Davis Chemical Co., 520 U.S. 17 (1997). Shoketsu Kinzoku Kogyo Kabushiki Co., Ltd. v. Festo Corp., 520 U.S. 1111 (1997) (“Festo III”). We considered the question en banc and held that the amendments were presumed to be related to patentability and therefore created an absolute bar to the invocation of the doctrine of equivalents. Festo VI, 234 F.3d at 574, 587-91.5 The Supreme Court again vacated and remanded, holding that an amendment did not raise a complete bar, and that there were three exceptions, namely that (1) the equivalent was “unforeseeable at the time of the application,” (2) “the rationale underlying the amendment [bears] no more than a tangential relation to the equivalent in question,” or (3) that “some other reason suggest[s] that the patentee could not reasonably be expected to have described the insubstantial substitute in question.” Festo VIII, 535 U.S. at 740-41.

In our second en banc, we held that rebuttal of the presumption of surrender was a question of law to be tried by a court and not a jury. Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 344 F.3d 1359, 1367 (Fed. Cir. 2003) (en banc) (“Festo X”). We explained that the latter two exceptions were legal questions to be determined based on the prosecution history and that neither exception applied. Id. at 1369-70. With respect to the first exception (foreseeability), we concluded that it too was a legal question but held that, because “[b]y its very nature[] objective unforeseeability depends on underlying factual issues,” district courts may hear expert testimony and consider other evidence relating to the foreseeability analysis. Id. at 1369. As no record on the issue of foreseeability had been made in the earlier district court proceeding, we remanded for the district court to determine: (1) “whether an ordinarily skilled artisan would have thought an aluminum sleeve to be an unforeseeable equivalent of a magnetizable sleeve in the context of the invention”; and (2) “whether a person of ordinary skill in the art would have considered the accused two-way sealing ring to be an unforeseeable equivalent of the recited pair of sealing rings.” Id. at 1371-72.

On remand, the district court found that Festo had failed to rebut the presumption of surrender by prosecution estoppel. So again, Festo appealed.

Case law -

In Graver Tank & Manufacturing Co. v. Linde Air Products Co., 339 U.S. 605 (1950), the Supreme Court stated that the doctrine of equivalents applies when the equivalent represents an “insubstantial” change from the claim language. Id. at 610. The Court also explained that “a patentee may invoke [the] doctrine [of equivalents] to proceed against the producer of a device ‘if it performs substantially the same function in substantially the same way to obtain the same result.’” Id. at 608 (quoting Sanitary Refrigerator Co. v. Winters, 280 U.S. 30, 42 (1929)). The Supreme Court in Warner-Jenkinson Co. v. Hilton Davis Chemical Co., 520 U.S. 17 (1997), considered whether the test for the doctrine of equivalents should be the “insubstantial differences” test or the “triple identity” test, which focuses on “the function served by a particular claim element, the way that element serves that function, and the result thus obtained by that element.” Id. at 39 (emphasis in original). The Court declined to choose one test because “[d]ifferent linguistic frameworks may be more suitable to different cases, depending on their particular facts.” Id. at 40.

The doctrine of prosecution history estoppel acts as a “legal limitation on the doctrine of equivalents.” Id. at 30. “[P]rosecution history estoppel limits the range of equivalents available to a patentee by preventing recapture of subject matter surrendered during prosecution of the patent.” Southwall Techs., Inc. v. Cardinal IG Co., 54 F.3d 1570, 1579 (Fed. Cir. 1995). The burden is on the patentee to establish that the reason for the amendment was unrelated to patentability. Warner-Jenkinson, 520 U.S at 33. If the patentee fails to meet this burden, the court must presume that the patentee “had a substantial reason related to patentability for including the limiting element added by amendment.” Id. If there is a substantial reason related to patentability “prosecution history estoppel would bar the application of the doctrine of equivalents as to that element.” Id. However, in Festo VIII, 535 U.S. at 740, the Supreme Court held that the patentee may prove that the amendment did not surrender the particular equivalent by demonstrating that one of three exceptions is met.

The present appeal defines what is foreseeable to what was known in the prior art. Judges Michel and DYK formed the majority, finding that the accused product (made by SMC) was a foreseeable alternative that could have been claimed, hence prosecution estoppel applies.

Here the sole question is whether the equivalent was “unforeseeable at the time of the application.” Festo VIII, 535 U.S. at 740-41. On remand from the Supreme Court, we concluded that “unforeseeable at the time of the amendment” meant “whether the alleged equivalent would have been unforeseeable to one of ordinary skill in the art at the time of the amendment.” Festo X, 344 F.3d at 1369. We noted that later-developed technology or technology that was not known in the pertinent prior art was “usually” not foreseeable. Id. However, we explained that “old technology, while not always foreseeable, would more likely have been foreseeable. Indeed, if the alleged equivalent were known in the prior art in the field of the invention, it certainly should have been foreseeable at the time of the amendment.” Id.

We have explained that the Supreme Court in Festo VIII “ties foreseeability to whether the applicant would have been expected to know of, and thus properly claim, the proposed equivalent at the time of amendment.” SmithKline Beecham Corp. v. Excel Pharms., Inc., 356 F.3d 1357, 1364 (Fed. Cir. 2004). Thus “the Supreme Court in Festo [does not] excuse[] an applicant from failing to claim ‘readily known equivalents’ at the time of application.” Id. Accordingly, we have consistently held that an equivalent is foreseeable when the equivalent is known in the pertinent prior art at the time of amendment. For example, in Amgen Inc. v. Hoechst Marion Roussel, Inc., 457 F.3d 1293, 1313 (Fed. Cir. 2006), we found that the patentee failed to establish a lack of foreseeability where “the patentee admittedly knew about the . . . equivalent at the time of the . . . amendment” and informed the examiner of the equivalent during prosecution.

[F]oreseeability does not require the applicant to be aware that a particular equivalent would satisfy the insubstantial differences test or the function/way/result test with respect to the claim as amended.

[A]n alternative is foreseeable if it is disclosed in the pertinent prior art in the field of the invention. In other words, an alternative is foreseeable if it is known in the field of the invention as reflected in the claim scope before amendment.

The question is not whether after the narrowing amendment the alternative was a known equivalent, but rather whether it was a known equivalent before the narrowing amendment. The purpose of an amendment typically is to avoid the prior art. If at the time of the amendment, the equivalent was known in the pertinent prior art, the applicant should not be able to recapture it simply by establishing that a property of the equivalent—irrelevant to the broader claim before amendment—was relevant but unknown with respect to the objectives of the narrower amended claim. In other words, an equivalent that is foreseeable as an alternative to the broader claimed feature does not become unforeseeable simply because the claimed feature is narrowed.

[T]he function/way/result test or insubstantial differences test is inapplicable to the question of foreseeability. An equivalent is foreseeable if one skilled in the art would have known that the alternative existed in the field of art as defined by the original claim scope, even if the suitability of the alternative for the particular purposes defined by the amended claim scope were unknown.

Judge Newman wails in dissent, assailing the majority finding as both unprecedented and illogical, that hindsight storms in with the majority finding -

[T]his court has confounded the issue by creating a new and incorrect criterion for the measurement of "foreseeability," the court now holding that an existing structure need not be recognized, or even recognizable, as an equivalent at the time of the patent application or amendment, in order to be "foreseeable" if it is later used as an equivalent. This is a significant departure from precedent, as well as from the Court's guidance in understanding the estoppels that arise when claims are amended during prosecution. Today's new rule further erodes the residue of the doctrine of equivalents, for its foreseeable result is to deprive amended claims of access to the doctrine of equivalents.

The panel majority holds that "An equivalent is foreseeable if one skilled in the art would have known that the alternative existed in the field of art as defined by the original claim scope, even if the suitability of the alternative for the particular purposes defined by the amended claim scope were unknown." That is, even if unforeseeable as a matter of fact, even if technologically unexpected or unlikely, the equivalent must be ruled to be foreseeable if the structure is later found to be a usable equivalent.

[T]he panel majority holds that this equivalent was foreseeable as a matter of law, and thus barred from access to the doctrine of equivalents.

The [Supreme] Court held that an accused structure that is not within the literal scope of amended claims, but that is the technological equivalent thereof, cannot be captured under the doctrine of equivalents if the claims before amendment did not exclude that structure and the equivalency was "readily" foreseeable. My colleagues now hold that such structures can be foreseeable as a matter of law, although the equivalency was unknown in fact. My colleagues also deem it irrelevant whether the accused structure could have been included in allowable claims.

Although the technological equivalency of an accused structure is determined as of the time of the infringement, foreseeability is determined as of the time of filing and amendment of the patent application. The Court so recognized in Festo VIII, in its remand for finding whether the assertedly equivalent aluminum alloy sleeve used by SMC was "unforeseeable at the time of the application." 535 U.S. at 740. We then remanded to the district court with instructions to find "whether an ordinary skilled artisan would have thought an aluminum sleeve to be an unforeseeable equivalent of a magnetizable sleeve in the context of the invention." Festo X, 344 F.3d at 1371-72.

The district court erroneously determined foreseeability based on the particular properties of the SMC device at the time of infringement, instead of on the knowledge at the time the '125 patent application was filed and presented.

My colleagues on this panel do not directly endorse the district court's reasoning, although similar reasoning is subsumed in the panel majority's holding that it is irrelevant whether the later-observed technologic equivalency was foreseeable at the time of the amendment. Instead, the panel majority rules that the aluminum alloy shield was retrospectively foreseeable at the time of the amendment because it later was used as an equivalent, although it was not known to be equivalent and would not have been deemed equivalent at the time of the amendment. Hindsight is not foreseeability. No error has been shown in the district court's finding that persons of skill in the field of the invention would not have deemed magnetizable and non-magnetizable sleeves to be equivalent at the time the '125 patent application was filed and prosecuted. It cannot be irrelevant that the then-existing knowledge in the field of the invention would not have deemed an aluminum alloy sleeve equivalent to a magnetizable metal sleeve in shielding magnetic leakage fields.

Evidence of foreseeability must be limited to prior art, not future art. It is not the correct interpretation of foreseeability, to rely on SMC's later equivalent use of an aluminum alloy sleeve to prove that the nonmagnetizable aluminum alloy was a foreseeable equivalent of a magnetizable metal, "at the time of the application" for the '125 patent.2 Foreseeability is determined as of the time of the application. The unforeseen does not become foreseeable after someone later discovers it. If the prior art does not support a finding of equivalency, the applicant cannot be charged with foreseeability of the equivalent.

My colleagues compound their error, in holding that "foreseeability does not require the applicant to be aware that a particular equivalent would satisfy the insubstantial differences test or the function/way/result test with respect to the claim as amended." Maj. op. at 1. Indeed, if the particular technology is not recognized as equivalent at the time of the application -- whether recognized by the applicant or by others of skill in the field -- that technology cannot be foreseeable. Foreseeability cannot be found as fact if the equivalence of magnetizable metal and aluminum alloy sleeves was not reasonably known at the time of filing and prosecution. In Graver Tank the Court explained: "An important factor is whether persons reasonably skilled in the art would have known of the interchangeability of an ingredient not contained in the patent with one that was." Graver Tank & Mfg. Co. v. Linde Air Prods. Co., 339 U.S. 605, 609 (1950). The inquiry surrounding when one becomes "aware" of equivalence must focus on the era of the application. If persons of ordinary skill in this field cannot be charged with foreseeing that an aluminum alloy sleeve would be a technological equivalent to a magnetizable metal sleeve, then the aluminum sleeve does not meet the criterion of foreseeability. The panel majority is incorrect in ruling that "the foreseeability requirement does not require the knowledge that the equivalent would satisfy the function/way/result test or the insubstantial differences test." Maj. op. at 18. How can a particular equivalent be foreseeable, if it was not known that the technology was equivalent in the context of the invention?

I also take note of the panel majority's unnecessary obfuscation of the technological criteria of equivalency as founded on Graver Tank, where the Court explained that "What constitutes equivalency must be determined against the context of the patent, the prior art, and the particular circumstances of the case," 339 U.S. at 609, the Court defining an equivalent as one that "performs substantially the same function in substantially the same way to obtain the same result.'" Id. at 608. The function/way/result test was endorsed by the court in Festo VIII, along with the insubstantial-differences test, and is no more susceptible to "endless bickering" as any other fact-dependent issue.

The panel majority states that it recognizes that the applicant can be charged with foreseeability only as to "[equivalents] known before the amendment, not equivalents known after the amendment," but then contravenes this statement, for my colleagues hold that it suffices to estop access to the doctrine of equivalents if the then-believed to be non-equivalent structure was a known structure in the field of the invention. My colleagues rule that it is irrelevant that the structure was believed not to be equivalent, as long as an original claim before amendment could have generally included a device having that structure. Such a complete bar based on amendment revives the approach rejected by the Court when it called our previous assault on the doctrine of equivalents a "complete bar by another name," Festo VIII, 535 U.S. at 741, the Court overturning the Federal Circuit's holding in Festo VI.

The fact of whether technologic equivalency was known cannot be irrelevant to foreseeability, for the foreseeability bar is directed to subject matter that was foreseeably equivalent at the time of filing and amendment. This is evident from Festo VIII 's guidance to "readily known equivalents." 535 U.S. at 740. If the equivalency of the accused technology would not have been "readily known" to a person of ordinary skill in the field of the invention, under proper application of the Court's guidance the "foreseeability" bar does not arise. In Festo VIII the Court ratified the value of the doctrine of equivalents to "ensur[e] the appropriate incentives for innovation," id. at 732, by rejecting this court's ruling that had led to "excessive uncertainty and burdens legitimate innovation." Id. at 737. The panel's holding today strays from controlling precedent as well as from logic.

The dissent points to yet another appeal, and further evidences the sorry proclivity of U.S. courts to embrace hindsight reasoning in patent law.