2. Doctrine of equivalents and rule of prosecution history estoppel
Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co. examined the question of when a patent-application amendment gives rise to estoppel. The doctrine of equivalents is intended to extend a patent holder's protection "beyond the literal terms in a patent." (Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co. (2002) 535 U.S. 722, 726 [122 S. Ct. 1831, 152 L. Ed. 2d 944, 62 U.S.P.Q.2D (BNA) 1705].) In doing so, the Court acknowledged that the doctrine "can create substantial uncertainty about where the patent monopoly ends." (Id. at 727.) This, in turns, makes it difficult for competitors to "determine what is a permitted alternative to a patented invention and what is an infringing equivalent." (Ibid.)
In Warner-Jenkinson Co. v. Hilton Davis Chem. Co., the Court addressed the uncertainty created by the doctrine of equivalents in ruling that competitors may rely on the public record of patent proceedings, which the Court referred to as the "prosecution history," to prevent potential infringement claims. (Warner-Jenkinson Co. v. Hilton Davis Chem. Co. (1997) 520 U.S. 17, 30 [117 S. Ct. 1040 | 137 L. Ed. 2d 146, 41 U.S.P.Q.2D (BNA) 1865].) "When the patentee responds to the rejection by narrowing his claims, this prosecution history estops him from later arguing that the subject matter covered by the original, broader claim was nothing more than an equivalent. Competitors may rely on the estoppel to ensure that their own devices will not be found to infringe by equivalence." (Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., supra, 535 U.S. 722, 727.)
In Festo, the patent holder claimed its patents for a magnetic rodless combustion cylinder were infringed by the defendant's similar product that used one sealing ring rather than Festo's two rings; it also used a non-magnetized cylinder in place of Festo's magnetized cylinder. Festo had amended its patent applications to add prior art references, the use of two sealing rings, and a magnetized sleeve for the cylinder.
The Court acknowledged the difficulties entailed in converting a tangible structure or series of drawings into a "verbal portrayal [that] is usually an afterthought written to satisfy the requirements of patent law." (Id. at 731.) The court quoted Autogiro Co. of America v. United States: "'This conversion of machine to words allows for unintended idea gaps which cannot be satisfactorily filled. Often the invention is novel and words do not exist to describe it. The dictionary does not always keep abreast of the inventor. It cannot. Things are not made for the sake of words, but words for things.'" (Ibid., quoting Autogiro Co. of America v. United States (1967) 384 F.2d 391, 397 [181 Ct. Cl. 55].)
The subjective nature of patent-specification interpretation was highlighted by the Court: "[T]he clearest rule of patent interpretation, literalism, may conserve judicial resources but is not necessarily the most efficient rule. The scope of a patent is not limited to its literal terms but instead embraces all equivalents to the claims described. See Winans v. Denmead, 56 U.S. 330, 15 How. 330, 347, 14 L. Ed. 717 (1854)." (Ibid.) The rationale for establishing the doctrine of equivalents was explained in Winans: "[T]he exclusive right to the thing patented is not secured, if the public are at liberty to make substantial copies of it, varying its form or proportions." (Winans v. Denmead (1854) 56 U.S. 330, 347 [15 How. 330, 347, 14 L.Ed. 717].)
Whereas the doctrine of equivalents "allows the patentee to claim those insubstantial alterations that were not captured in drafting the original patent claim but which could be created through trivial changes," there are instances when "'by the amendment [the patentee] recognized and emphasized the difference between two phrases . . . [and] thus disclaimed [what] must be regarded as material.'" (Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., supra, 535 U.S. 722, 734, quoting Exhibit Supply Co. v. Ace Patents Corp. (1942) 315 U.S. 126, 136-137 [86 L.Ed. 736, 62 S.Ct. 513].) This is where the doctrine of prosecution history estoppel comes into play:
"Prosecution history estoppel ensures that the doctrine of equivalents remains tied to its underlying purpose. Where the original application once embraced the purported equivalent but the patentee narrowed his claims to obtain the patent or to protect its validity, the patentee cannot assert that he lacked the words to describe the subject matter in question. The doctrine of equivalents is premised on language's inability to capture the essence of innovation, but a prior application describing the precise element at issue undercuts that premise. In that instance the prosecution history has established that the inventor turned his attention to the subject matter in question, knew the words for both the broader and narrower claim, and affirmatively chose the latter." (Id. at 734-35.)
The Court indicated its intention to ensure prosecution history estoppel is applied conservatively:
"Estoppel arises when an amendment is made to secure the patent and the amendment narrows the patent's scope. If a § 112 amendment is truly cosmetic, then it would not narrow the patent's scope or raise an estoppel. On the other hand, if a § 112 amendment is necessary and narrows the patent's scope -- even if only for the purpose of better description -- estoppel may apply. A patentee who narrows a claim as a condition for obtaining a patent disavows his claim to the broader subject matter, whether the amendment was made to avoid the prior art or to comply with § 112. We must regard the patentee as having conceded an inability to claim the broader subject matter or at least as having abandoned his right to appeal a rejection. In either case estoppel may apply. (Id. at 736-37.)
The court stopped short of ruling that estoppel is a complete bar to the inventor asserting infringement and decided instead to adopt the flexible-bar rule the Court of Appeals rejected as unworkable:
"[L]anguage remains an imperfect fit for invention. [When the inventor narrows via amendment, it] may demonstrate what the claim is not; but it may still fail to capture precisely what the claim is. There is no reason why a narrowing amendment should be deemed to relinquish equivalents unforeseeable at the time of the amendment and beyond a fair interpretation of what was surrendered. Nor is there any call to foreclose claims of equivalence for aspects of the invention that have only a peripheral relation to the reason the amendment was submitted. The amendment . . . shows only that [the inventor] was familiar with the broader text and with the difference between the two. As a result, there is no more reason for holding the patentee to the literal terms of an amended claim than there is for abolishing the doctrine of equivalents altogether and holding every patentee to the literal terms of the patent." (Id. at 738.)
In its conclusion, the Court circled back to the need to begin the investigation of alleged patent infringement with a literal interpretation of the application, which is assisted by the extrinsic evidence available in the prosecution history:
"[T]he interpretation of the patent must begin with its literal claims, and the prosecution history is relevant to construing those claims. When the patentee has chosen to narrow a claim, courts may presume the amended text was composed with awareness of this rule and that the territory surrendered is not an equivalent of the territory claimed. In those instances, however, the patentee still might rebut the presumption that estoppel bars a claim of equivalence. The patentee must show that at the time of the amendment one skilled in the art could not reasonably be expected to have drafted a claim that would have literally encompassed the alleged equivalent." (Id. at 741.)
As with contract interpretation, courts prefer to resolve patent disputes based on the four corners of the document, which in most cases is the patent application. However, it may be unreasonable to expect software-patent applicants to express all the nuances of their invention in language sufficient to prepare for all potential infringements, and to defend against claims of invalidity. The courts have recognized -- sometimes grudgingly -- the need for flexibility in applying existing case law and statutes to claims of patent infringement and invalidity.
Of course, potential infringers need sufficient information to avoid running afoul of a patented invention, and to devise their own inventions. The tremendous increase in software-patent cases in recent years is not only the result of so-called patent trolls. Software by its nature defies easy application of existing patent regulations. Critics claim that uncertainty in software patent awards and lawsuits have been a boon to lawyers and a drain on the courts, but most software-patent suits are brought in good faith by holders with a legitimate goal of protecting their property rights.