Chapter §16.03 Infringement Under the Doctrine of Equivalents

• Jurisdiction: United States

§16.03 Infringement Under the Doctrine of Equivalents

United States patent law also recognizes the possibility of "nonliteral" or "nontextual" infringement under the doctrine of equivalents.¹⁰ Notably, the doctrine of equivalents is entirely judge-made law; it does not appear in the Patent Act.¹¹ Although the Supreme Court has repeatedly reaffirmed the doctrine's viability, it has also pointedly recognized that "Congress can legislate the doctrine of equivalents out of existence any time it chooses."¹²

[A] Historical Background and Policy Underpinnings

The doctrine of equivalents has its U.S. genesis in early Supreme Court patent cases such as Winans v. Denmead.¹³ There the Court found that a patent claiming the configuration of a railroad coal car having a cylindrical, cone-like shape was infringed by an accused car shaped in cross-section like an octagon. Winans does not expressly refer to a doctrine of equivalents, but such a doctrine is implied in the result of the case.

Claiming practice at the time of Winans (i.e., prior to the Patent Act of 1870) was much more of a central claiming regime than the peripheral claiming system used today in the United States. Under the central claiming regime, a claim recited the "preferred embodiment" of the invention but was deemed as a matter of law to include all equivalents to (i.e., substantially similar copies of) that preferred embodiment.¹⁴ The Winans Court recognized that

[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. And, therefore, the patentee, having described his invention, and shown its principles, and claimed it in that form which most perfectly embodies it, is, in contemplation of law, deemed to claim every form in which his invention may be copied, unless he manifests an intention to disclaim some of those forms. ¹⁵

Thus, the central claiming regime in effect at the time of Winans recognized that the patentee's invention was not truly protected unless the patent prohibited not only the unauthorized making of identical copies but also the making of "substantial" copies thereof. As the U.S. patent system eventually transitioned from central claiming to the peripheral claiming system used today, the underlying goal of protecting the patentee to the full extent of her contribution has been maintained and resurrected, so to speak, in the guise of the judicially recognized doctrine of equivalents.

As the Court in Graver Tank & Mfg. Co. v. Linde Air Prods. Co.¹⁶ characterized it, the essential thrust of the doctrine of equivalents is that "one may not practice a fraud on a patent."¹⁷ The doctrine of equivalents is a judicial response to the practical reality that if a patent can be avoided by copying the claimed invention while making a minor, insubstantial change of just enough scope to take the copied matter outside of the literal boundaries of the claim, the right to exclude that the patent bestows will not be worth very much. If the value of a patent is lessened by an inability to stop nonliteral copyists, the economic incentive to innovate that the patent represents is likewise diminished and society suffers a resulting impoverishment of new inventions.

In addition to this economic/fairness rationale, the doctrine of equivalents also serves as an important linguistic safety valve. Judicial recognition of the doctrine of equivalents reflects that words are not always the optimal medium for conveying inventive concepts. Many inventions are best embodied in physical prototypes, mechanical drawings, molecular modeling, or other nonlingual scientific and technical media. Particularly when dealing with "pioneer" inventions involving state-of-the-art technology for which there may not yet exist a recognized, well-established vocabulary, the doctrine of equivalents is an essential tool for conveying to the patent owner the full benefit of her invention.¹⁸

[B] Tension with the Notice Function of Claims

The policy rationales that support the doctrine of equivalents admittedly conflict with the principle that claims are intended to provide clear, advance notice to competitors of the scope of the patentee's right to exclude.¹⁹ As the Supreme Court summed it up, "[a] patent holder should know what he owns, and the public should know what he does not."²⁰ A certain tension arises when courts find liability under the doctrine of equivalents, because they are extending the right to exclude beyond that denoted by the literal boundaries of the patent's claims.²¹ How useful is the advance "notice" provided by patent claims if it is essentially ignored for equitable reasons in applying the doctrine of equivalents? This undeniable tension has been succinctly described as the "fair protection-certainty conundrum."²²

[C] All-Limitations Rule

In Warner-Jenkinson Co. v. Hilton Davis Chem. Co.,²³ the Supreme Court instructed that the fair protection-certainty conundrum can be minimized by vigilant application of the all-elements rule, which requires that the doctrine of equivalents be applied on a claim limitation-by-limitation basis rather than to the "invention as a whole."²⁴ The Court stated:

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. ²⁵

For example, if a patent claim recites "a widget comprising lever A, pulley B, and spring C," the doctrine of equivalents must be separately applied to determine if (1) lever A of the claimed invention is equivalently met in the accused device; (2) if pulley B of the claimed invention is equivalently met in the accused device; and (3) if spring C of the claimed invention is equivalently met in the accused device. If any of these three limitations is not met at least equivalently (if not literally), there can be no infringement.

[1] Defining a "Limitation"

Applying the all-limitations rule requires that one first identify each limitation of a claim. Often the task of determining what portion of a patent claim represents a discrete limitation (also sometimes referred to as an element)²⁶ is not so straightforward. The answer will depend on the level of generality that the court reviewing the matter chooses to adopt.

For example, consider the interpretation of a patent claim to a widget "having a plastic tube." The district court may consider "plastic" and "tube" to be two separate limitations, such that each limitation would separately need to be met in the accused device in order to find infringement. Thus, if the accused device was a widget that used a steel pipe rather than a plastic tube, the fact finder in the second step of the infringement analysis (whether judge or jury) would need to separately determine (1) whether the steel used in the accused widget's pipe is insubstantially different from the plastic of the claimed tube, and (2) whether the pipe of the accused widget is insubstantially different from the claimed tube. With respect to question (1) the fact finder might evaluate the insubstantiality of the differences by asking whether steel performs the same function in the accused widget's pipe as plastic does in the claimed tube, in substantially the same way, to achieve substantially the same result. Known interchangeability of steel and plastic in widgets also might be relevant to the analysis. For question (2), the fact finder might evaluate the insubstantiality of the differences by asking whether a pipe performs the same function in the accused widget as a tube does in the claimed widget, in substantially the same way, to achieve substantially the same result. Known interchangeability of pipes and tubes in widgets also might be relevant.

Alternatively, the district court interpreting the claim of this example may adopt a higher level of generality and choose to treat the phrase "plastic tube" as one single limitation rather than two separate limitations. In that case the fact finder would need to determine whether the accused widget's steel pipe is insubstantially different from the claimed widget's plastic tube. In order to analyze the extent of that difference, the fact finder might ask whether the steel pipe performs the same function in the accused widget as the plastic tube does in the claimed widget, in substantially the same way, to achieve substantially the same result. Known interchangeability of steel pipes and plastic tubes in widgets also might be relevant.

As this example attempts to illustrate, the level of granularity that the district court applies when enumerating the individual limitations of a claim can have a very real impact on the determination of technologic equivalency in the second step of the infringement analysis. Generally speaking, an accused infringer will attempt to establish the greatest possible number of limitations, making more burdensome the patentee's job of having to establish insubstantial differences with respect to each such limitation. In contrast, a patentee generally will seek to minimize the number of limitations so as to lessen her burden.

Determining what the limitations are in a patent claim to biotechnological subject matter may represent an even greater challenge. For example, consider a claim reciting

a purified, isolated DNA molecule comprising the nucleotide sequence AAGGTCAGGTCA. ²⁷

What are the pertinent limitations of this claim? Is a single nucleotide, A (the base adenine), the relevant limitation to be met in the accused molecule? Or is the pertinent limitation in this example a codon of three nucleotides, AAG (which together form the amino acid lysine)? Or is it an even longer stretch of...