treatise02

1. The Meaning of the Essential Part

1-1. Introduction

In the Supreme Court decision in the “Infinite Motion Ball Spline Bearing Case” (February 24, 1998), which is said to have affirmed the doctrine of equivalence as a general legal principle, the first requirement for the application of the doctrine of equivalence was stated as “the different parts must not be essential parts.”

In determining this first requirement, it is necessary to identify the essential parts of the patented invention. Indeed, the identification of these essential parts is arguably the most critical factor in defining the scope of patent rights (including equivalents). After all, the issue at hand is whether a product or the like incorporates the essential parts of the patented invention, thereby falling within the scope of the technical scope of the patent.

In other words, under the patent law’s conditions for protecting inventions—which involve conducting a patentability examination on inventions described in the claims as the subject matter for which rights are sought and disclosed in the specification, and granting exclusive rights to protect them—extending the effect of the patent right to objects or methods that do not incorporate the essential elements of the patented invention would contradict the purpose of the patent law.

In the following, we will examine the important matters concerning the determination of the scope of rights, namely, the “essential elements” that should be based on what factors and under what principles.

1) Supreme Court Case Law Commentary, “Legal Times, Vol. 53, No. 6,” by Ryōichi Mimura, p. 172
2) “Case of Ball Spline Bearing for Infinite Motion (Supreme Court Decision of February 24, 1998, Supreme Court Case No. Hei 6 (O) 1083)”

1-2. Definitions in lower court rulings

Following the aforementioned Supreme Court ruling, when the issue of equivalence arose in lower courts, the first requirement mentioned above—that the portions of the claimed invention that differ from the product or the like described in the claims are not essential elements of the patented invention—was examined, and the definition was established as follows:

“The essential elements of the patented invention are the features of the claimed invention that constitute the unique problem-solving means of the patented invention.”

“The characteristic parts of the configuration of the patented invention described in the claims that form the basis for the unique problem-solving means of the patented invention” (Tokyo District Court, March 23, 2012)3)

“The parts of the configuration of the patented invention described in the claims that produce the unique effects of the patented invention” (Osaka District Court, May 27, 1999)4) (Osaka High Court also adopted the same definition)5)

Furthermore, the common definition in the above judgments is that “in other words, it refers to the part that, if replaced by other configurations, would be evaluated as a separate entity from the technical concept of the patent invention as a whole.”

The common definition provided in the above judgments clarifies the universal meaning of “essential part.” That is, the “essential part” refers to the important elements of a patent invention that, when compared with the technical concept of the patent invention and the subject product, would render the subject product incapable of being an infringing product if it did not utilize that “part” (technical concept).

Although the term “essential part” is used, this does not necessarily mean a part of the elements of the patented invention. An essential part must be the technical idea that constitutes the patented invention as such, and it must be a technical idea that can solve the problems of the prior art on its own.While it constitutes the core of the technical concept described in the claims, it does not refer solely to the parts that differ from prior art.

In other words, the essential part may be defined as encompassing all the elements of the invention described in the claims (when the description in the claims aligns with the core of the patented invention), or it may refer to the core technical concept of the invention extracted by excluding certain parts from the configuration described in the claims.

The “essential part” is difficult to grasp through general or abstract consideration, and it is necessary to first examine it using specific examples.

2. Consideration Using Specific Examples

2-1. As a specific example, we will use an invention related to contact lenses. In reality, the principle of contact lenses is said to have been conceived by Leonardo da Vinci in the early 16th century and later developed by Descartes in the 17th century6); however, for the purposes of this discussion, we will consider this principle as having been conceived for the first time.

2-2. [Example 1]

Patent invention X1: Invention of the contact lens itself (so-called pioneer invention)

6) Information from the Internet (http://www.jutoku.com/kontakuto_index6-1.html)

2-3. Consideration of the essential parts of Example 1

How are the “essential parts” of the patent invention X1 defined?

① First, the differences between the structure of the invention X1 described in the claims and the structure of the target product Y1 are the lens material, namely, a ‘glass’ lens and a “lens manufactured from plastic.”

　 Does this “glass” component constitute an essential element of the present patent invention? Considering that only eyeglasses existed previously and the problems and functions that the present patent invention sought to solve, it is interpreted that the fact that the ‘lens’ is made of “glass” is not an indispensable element and does not constitute an essential element.

Then, what is the “principle of solution” to the prior art problem addressed by the present invention, or what are the “characteristic parts” necessary to satisfy the patent requirements? Considering these from the above conditions, the essential part of the present invention X1 is considered to be the “lens for correcting vision by directly contacting and attaching to the eyeball” or the “method of correcting vision by directly attaching a lens to the eyeball” as stated in the claims.In other words, the idea of directly attaching a lens to the eyeball is the essential part.

 As a conclusion of the judgment on the first requirement, the differences between the patent invention X1 and the target product Y1 are not essential parts of the invention X1.

② In this case, the “essential part” is not understood as having all the structural requirements described in the scope of the claims, but rather as having the structural requirements excluding the requirement of “glass.”By excluding some of the structural elements, the scope covered by the “essential part” is expanded. At the very least, it is broader than the scope that includes all the structural elements listed in the claims. This means that the core part of the invention described in the claims is considered the essential part.

③ Regarding the limitation of “glass”

At the time of filing, the term ‘lens’ referred exclusively to “glass,” so the term “glass lens” was used. However, when product Y1 appeared, it became clear that this limitation was unnecessary.

Therefore, in the case of the above determination of the first requirement, if the second to fifth requirements are also satisfied, the target product Y1 is deemed to fall within the scope of equivalence, and as a result, the inclusion of the “glass” requirement in the claims is deemed to be remedied. The validity of this determination will be discussed later (4.).

2-4. [Example 2]

Patent Invention X2: A soft contact lens made of plastic with a high moisture content

2-5. Consideration of the essential parts of Example 2

① The differences between the structure of Patent Invention X2 and the structure of the target product Y2 lie in the materials of the lenses. Specifically, the lens material of Patent Invention X2 is plastic “A,” while the lens material of the target product Y2 is plastic “B.”

In this case, whether the lens material “A” of Patent Invention X2 constitutes an essential part of the invention is a point of contention. Patent Invention X2 improves upon conventional plastic soft contact lenses by enhancing water content. This improvement was achieved through the selection of materials, which constitutes a characteristic feature of the invention. In other words, soft contact lenses manufactured using material ‘A’ are the “solution principle” to the conventional problem.

Therefore, the claim that the “soft contact lens for vision correction that is directly applied to and worn on the eyeball” is the only essential part of the invention, disregarding the lens material, is not permissible. Rather, the claim that the “lens material ‘A’” is an essential part of the invention must be added as a claim element.

The lens material of the target product Y2 is “B,” which has non-absorbent properties, and its function is to improve oxygen permeability. Therefore, the two are different in their essential parts. Thus, the first requirement that “the different parts are not essential parts of the patented invention X2” is negated.

As a conclusion of the judgment on the first requirement, the target product Y2 is not equivalent to the configuration of the patented invention X2 and does not fall within its technical scope.

② In this determination, the essential parts of the patent invention X2 are understood as the scope defined by the same structural requirements as those described in the claims of the invention.

2-6. Consideration of cases where the technical background (prior art) differs (hereinafter referred to as “modified example”)

In the above Example 1, at the time of filing, the prior art was limited to “so-called eyeglasses worn on the ears or nose,” but if ‘plastic’ was also known as a lens material in addition to “glass,” would the conclusion regarding the determination of essential elements change?

Since “contact lens lenses” did not exist at the time, the fact that Patent Invention X1 is a groundbreaking pioneer invention remains unchanged.

 However, at the time of filing, since the scope of the patent claims was stated as “glass lenses” despite the fact that, at the time, plastic was also available as a lens material in addition to glass, it is possible to conclude that the requirement for “glass” should be added when determining the essential elements.This judgment would be more clearly justified if the specification or examination process had mentioned the safety of “glass lenses” when directly fitted to the eyeball (even without comparing them to plastic).

3. Differences in the conclusions of the first example, second example, and the above modified examples

3-1. Regarding Patent Inventions X1 and X2

The claims of Patent Inventions X1 and X2 both describe contact lenses that explicitly specify the material of the lens, and the level of limitation of the structural elements is the same. Additionally, in terms of their relationship to the target products, they share the common feature that the explicitly specified lens materials differ between the target products Y1 and Y2.

In such a situation, while one (Example 1) satisfies the first requirement and the other does not, where does this difference originate?

The two patent inventions differ significantly in terms of their differences from prior art. Invention X1 is a groundbreaking invention that first patented the “contact lens” technology, which did not exist prior to its invention, and can be considered a pioneer invention.On the other hand, invention X2 is an improvement on an existing technology, namely “soft contact lenses,” and thus represents an improvement on a technology that had already reached a certain level of maturity.

 In this way, the essential part of a patent invention is defined by its relationship to the prior art (publicly known technology) that existed at the time of filing, which determines the scope of the invention. This means that the scope of the invention varies depending on whether it represents a groundbreaking leap forward from the prior art,such as a pioneering invention (like the aforementioned “contact lens”) where no direct prior art exists. In such cases, the essential part of the invention may be defined by excluding certain elements, even if they are explicitly stated in the claims, provided that those elements are not indispensable for solving the problem.

On the other hand, in the case of improvements to existing technology, it is not possible to exclude the structural elements of the improved portion when defining the essential elements. This is because such structural elements are indispensable for solving the problem. Therefore, it was not possible to exclude the material requirements when determining the essential elements of the above invention X2.

In the above example, by comparing a clear pioneer invention and an improvement of prior art, we showed that even if the claims are limited to the same level, the scope of the essential elements differs. However, this is not immediately determined by whether it is a pioneer invention or an improvement, but ultimately depends on the breadth of the claims in relation to the prior art.

Even if an invention is a pioneer invention, if it is possible to claim only the essential elements necessary to solve the problem, the essential elements of the invention will be defined as including all the elements of the claims. Conversely, even if an invention is an improvement, if it is later determined that the claims are overly restrictive, the essential elements may be defined by excluding certain elements.

However, actual pioneer inventions are not always as simple as the above examples; rather, they are often complex, highly sophisticated, and specialized. In such cases, it is likely to be extremely difficult to draft the claims without any unnecessary limitations at the time of the initial filing. This is likely to be more challenging than in cases of improvement inventions where the improvements over prior art are clear.For this reason as well, it is considered reasonable to allow a broader definition of the essential elements in the case of inventions with a high degree of pioneering innovation.

3-2. Regarding “Variations”

In the examination of the above variations, although the description of the claims was the same, a different conclusion was reached regarding the identification of the essential elements compared to the first example. The elements that differed from the first example were the relationship between the invention described in the claims and the prior art (further, the content of the specification).

Specifically, at the time of filing, plastic was also known as a general lens material (the specification mentions the safety of glass), and the claims included the term “glass lens.”

After reviewing the prior art and the entire specification, if it is reasonable for others to consider that the lens being made of glass is part of the invention’s features, it should be determined that “glass” is one of the requirements for defining the essential elements to ensure legal stability.

In this way, even if the invention is a pioneer invention and the description in the claims is the same, the background technology, the description in the specification, and the examination process may influence the determination of the essential elements of the invention.

Furthermore, even if “plastic” is known as a general lens material, if there are difficulties in terms of safety, such as the selection of materials, to make it suitable for direct contact with the eyeball, the second requirement of “easily replaceable” may not be satisfied.In such a case, even if it is determined that “glass” is not a requirement for defining the essential part, equivalence would not be recognized. However, in a situation where there were difficulties in adopting ‘plastic’ material, this would likely be taken into account in the determination of the essential part, so ultimately, the likelihood that “glass” would be required in the determination of the essential part would be higher.

3-3. Determination of Essential Elements

From the above specific example, it can be understood that, ultimately, when determining essential elements, it is necessary to judge to what extent the exclusion or narrowing of the structural requirements explicitly stated in the claims is permissible from the perspective of legal stability.In making this determination, factors such as the inventiveness (pioneering nature) of the invention, as well as the contribution of the invention to society in general, should be considered, taking into account the purpose of the Patent Act to promote the development of industry and thereby contribute to the public welfare (Patent Act, Article 1).

However, even when referring to pioneering nature, in the world of continuously advancing technology, the difference between a pioneering invention and an improved invention is always a matter of degree, and the “value of the invention” in terms of its contribution to society cannot be determined solely by whether it is a pioneering invention or an improved invention (even improved inventions may have significant social contributions). Therefore, it is considered that this determination is not straightforward in practice.More specifically, the difficulty of defining the “essential part” lies in the fact that, when an infringement occurs, it is necessary to make a legal judgment on whether the core of the invention that should be protected, i.e., the “value of the invention” sufficient to exclude the claimed elements from the scope of protection and expand the scope of protection, exists within the invention described in the claims, even if this would undermine legal stability.

Moreover, it is precisely because this is such a difficult judgment that the proper identification of the essential elements is essential for determining the appropriate scope of rights.

4. Whether it is appropriate to remedy limited descriptions in the scope of the patent claims due to errors in the scope of the patent claims by applying the doctrine of equivalents.

4-1.

The basis for extracting the “essential elements” of a patented invention and recognizing the scope of equivalents beyond the literal scope of the claims is, as stated in the aforementioned Supreme Court decision, the “difficulty of anticipating all future infringement scenarios at the time of filing and describing them in the claims,” and the fact that “allowing substitution with substances or technologies that become known after filing would diminish the incentive to invent, contravene the objectives of patent law, and ultimately violate social justice,

This principle is based on the concept of equity.

Furthermore, the World Intellectual Property Organization (WIPO) Draft Patent Law Treaty states that “the scope of protection conferred by a patent is determined by the claims” (Article 21(1)(a)), and adds that “claims shall be interpreted in a manner that combines fair protection for the patent owner with a reasonable degree of legal certainty for third parties. In particular, claims shall not be limited to their literal meaning.”“ (same paragraph (b)). This provision affirming the doctrine of equivalents cannot be interpreted as distinguishing between limitations resulting from error and those not resulting from error.

4-2.

Furthermore, the scope of the doctrine of equivalents extends beyond the scope directly defined by the wording of the claims, and the fact that the scope is in question means that the claims are, at least as a result, ”too narrow.”

For example, if the element “vacuum tube” was listed as one of the claim elements in the claims of a patent for an innovative “device invention,” and this element was later replaced with ‘transistor’ after the patent application was filed, it could be argued that there was no mistake in the description, as at the time of filing, the only component with amplification functionality was the “vacuum tube.”Similarly, it is difficult to determine whether it was an error to describe “glass lens” at a time when “lens” was only considered to be made of glass.In both cases, when infringement became an issue, it could be argued that the functional description “amplification means” should have been used, or that limiting the description to “lens” would have been sufficient, i.e., that the limitation was overly restrictive and that the requirement should not have been excluded when defining the essential elements.In any case, it is not easy to determine whether the limitation was unavoidable at the time of filing or merely a matter of carelessness, and it is also a matter of degree.

 Ultimately, whether a limitation due to an error can be remedied by the doctrine of equivalents depends on whether the essential elements are accurately determined.It is not the case that the doctrine of equivalents does not apply at all in cases of mere errors, nor is it the case that errors do not result in disadvantages in the application of the doctrine of equivalents.

In other words, at the time of infringement, when it is determined that the limitation is “excessive,” it is important to make an appropriate legal judgment, taking into consideration the value of the invention and legal stability, as to whether the “constitutive element” should be excluded in the determination of the essential elements.

5. Scope of Equivalence When the Essential Elements Are Determined to Include All the Claimed Elements

In cases where there is no such excessive limitation, i.e., where the invention is described in the claims with the broadest possible scope relative to the prior art, without any unnecessary limitations, and where only the minimum necessary elements required to solve the problem are described, how would the essential elements be determined?In this case, since the invention cannot be established as a patented invention even if any of the elements are excluded, all the requirements for the description of the claims are considered to be the requirements for defining the “essential elements.” Therefore, in such a case, considering only literal infringement, appropriate protection of the patented invention is ensured, and the application of the doctrine of equivalents is unnecessary.

For example, in the case of the above Example 2, where all the elements of the claims are considered to be elements of the essential parts, this is a case where the invention is claimed without unnecessary limitations. The same applies to Example 1, where “glass” is not specified and only “lens” is stated.

In such cases, when it is determined that the differences between the patented invention and the target product, etc., are not essential parts (i.e., when the essential parts are common), the target product, etc., is deemed to include all the elements of the claims. Therefore, in such cases, the target product falls within the scope of the claims and does not involve the issue of equivalence regarding a broader technical scope beyond the literal scope of the claims.

Using the above Example 2 as a concrete example, consider the patent invention X2 (“contact lenses manufactured from plastic material ”A“”). If the target product Y3 is “composed of plastic material ‘A’ and has a special shape at the outer periphery that does not injure the eyeball,” then the target product Y3 is a product that incorporates all the essential elements of the patent invention X2.

This product Y3 is an invention that incorporates all the elements of the patented invention X2 and adds new value, i.e., it is an “utilization invention” of the patented invention X2. This example ultimately falls under the issue of the scope of the wording infringement (i.e., it should be deemed to fall within the technical scope) rather than the issue of equivalence.

Nevertheless, if the five criteria for equivalence are applied to the structural feature of the lens’s outer peripheral shape, which is the difference between the two, there is a risk of reaching an erroneous conclusion.

First, as mentioned above, the differing part “the outer peripheral part is shaped in a special way to prevent injury to the eyeball” is not considered an essential part of the patent invention X2, and substitutability is likely to be affirmed since material “A” is used.However, if the third requirement is denied on the grounds that the adoption of the “shape of the outer periphery of the lens” is difficult because it is a feature recognized as having inventive step as an improved invention, this would constitute a significant error.This is because the act constituting literal infringement would not even fall under the doctrine of equivalents.

 From this, it can be concluded that the doctrine of equivalents should only be applied when the “essential part” of the patent invention is interpreted as a component that is relaxed (excluded) from the claim’s description of the components.In other words, it is only when some of the elements of the claims are replaced (differ) that the issue of equivalence beyond the scope of the claims arises.

Applying the five criteria to cases where elements other than the requirements for the description of the claims differ, as described above, is not appropriate when applying the criteria for equivalence established by the Supreme Court.

6. Relationship with the other four requirements

6-1. Significance of the first requirement (essential part) in relation to the other four requirements

The first through fifth requirements are “and” conditions, and if any one of them is not satisfied, the application of the doctrine of equivalents is not recognized.

Therefore, even if the other four requirements are deemed to be satisfied, if the first requirement is not satisfied, i.e., if the differing parts constitute essential parts, the doctrine of equivalents does not apply. However, is such a case actually possible? If not, then in practice, the first requirement would be irrelevant, and consideration of the other four requirements alone would suffice. This will be examined below.

6-2.Consideration in relation to the second requirement (substitutability) and the third requirement (ease of substitution)

Regarding the requirements of substitutability and ease of substitution, considering the invention X2 in the above [Example 2], if the target product Y4 is a “soft contact lens made of material C,” and material C not only has the same moisture content as A but also has oxygen permeability, what would be the case?

At the time of the infringing act, if it was known that the plastic material “C” had the same water content as “A,” the second and third requirements would be satisfied. However, as mentioned above, the characteristic of the patented invention X2 is that it uses material “A,” and this cannot be excluded from the essential elements of the claim. Therefore, the target product Y4 does not satisfy the first requirement, and the doctrine of equivalents does not apply.In this way, the determination of the first requirement serves to prevent the scope of the doctrine of equivalents from expanding excessively by setting the timing for assessing substitutability at the time of infringement (the inhibitory function of the first requirement regarding the expansion of equivalence).

Additionally, we will consider the relationship between the third requirement and the first requirement when the first requirement is satisfied. According to the aforementioned “Supreme Court Case Law Commentary,” “the requirement regarding essential parts has traditionally been explained as ‘identity of technical ideas’ or ‘identity of the underlying solution principle.’”7) Furthermore, it is stated that “the present judgment used the expression ‘essential part of the patented invention’ regarding this requirement because it appears to have deliberately avoided the expression ‘identity of the technical idea’ in order to address the criticism that ‘evaluating the technical idea as identical is synonymous with recognizing equivalence, and listing the identity of the technical idea as a requirement for equivalence would constitute a tautology (synonymous repetition)’”8).

If the commonality of essential parts is interpreted as the identity of technical ideas, then if the differences between the two are determined to be non-essential parts (satisfying the first requirement) through proper judgment, it can also be considered that the second requirement (substitutability) and the third requirement (ease of substitution) are simultaneously satisfied.

However, in the above [Example 1], the use of “plastic material” as a contact lens is not merely a transfer but was adopted after extensive trial and error to ensure safety, thereby significantly altering the nature of contact lenses. In such cases, even if the first requirement is satisfied, it may be deemed that the second requirement (substitutability) is not satisfied.

Nevertheless, even in such cases, the background of the relevant technical field should be considered when determining the essential elements of the patent invention. Therefore, “glass” would also become a criterion for defining the essential elements, and the first requirement itself might not be satisfied.

Nevertheless, the issue of the difficulty of using plastic as a contact lens material should be discussed separately as a matter for determining the third requirement, as this would maintain the clarity of the judgment. Therefore, it is considered that there is significance in separately determining the third requirement after determining the fulfillment of the first requirement.

7) Footnote 1) “Supreme Court Case Law Commentary,” pages 194, lines 1–2
8) Footnote 1) “Supreme Court Case Law Commentary,” page 195, line 17 to page 196, line 1

6-3. Relationship with the Fifth Requirement (Absence of Estoppel, etc.)

Using the above “example of modification,” in a situation where both glass and plastic were selectable as lens materials at the time of filing, if the safety of “glass lenses” was described in the specification or during the examination process in relation to direct application to the eyeball, it is considered that “glass” would be deemed a requirement in determining the essential elements.

Therefore, “glass contact lenses” and “plastic contact lenses” would differ in their essential parts. In such a case, if it is determined that merely stating the safety of glass does not constitute an intentional exclusion of plastic materials, and the fifth requirement is deemed satisfied, the application of the doctrine of equivalents would be restricted by the first requirement.

7. Burden of Proof and Order of Determination for the First Requirement7

7-1.

The burden of proof for the first requirement lies with the patent holder. In the aforementioned Supreme Court ruling, the first requirement is “that the right portion is not an essential part of the patented invention,” and from this wording, it can be inferred that the patent holder is responsible for asserting and proving that the differing portion is not an essential part.

7-2.

If the first requirement is considered to be a judgment on the identity of the technical concept, although it is listed as the first requirement, it is not necessarily required to be made prior to other requirements. There is also the view that the first requirement should be judged as part of a comprehensive judgment after considering the second requirement or other requirements.

In particular, it is closely related to the judgment on the second requirement.If the first requirement is satisfied, i.e., if the essential part remains unchanged even when the portion is substituted, the substitution occurs in a situation where the same effect is achieved, and thus the possibility of substitution is satisfied.

However, even in such cases, determining what constitutes the essential part of the patented invention—which is part of the judgment of the first requirement—is necessary for assessing other requirements and should therefore be conducted beforehand.In other words, if the essential elements of the patented invention are not defined, it is difficult to assess other requirements such as substitutability, obviousness, or estoppel. Additionally, as mentioned earlier, if the requirements for the description of the scope of the claims and the requirements for the essential elements are consistent, the issue of equivalence does not arise. Therefore, it is considered that identifying the essential elements should be the first step in assessing infringement.

8. Conclusion

As discussed above, in determining the first requirement, the “essential elements” are extracted based on the description of the claims themselves, the detailed description in the specification, prior art, and the application history, as well as pre-application peripheral technology.Therefore, even if certain limiting requirements exist in the description of the claims, the core idea of the claims may be extracted, thereby excluding such limiting matters. This can be regarded as the first step in expanding the scope of rights from the literal scope of the claims to the scope of equivalents. However, as mentioned above, the determination of the first requirement also serves to prevent the application of the doctrine of equivalents from being overly expanded.

Therefore, the determination of the essential elements that possess both the functions of expansion and restriction in the delimitation of the scope of rights is a highly important matter. It is only through such a determination made under a proper balance between legal stability and the protection of the value of inventions that an appropriate and moderate scope of rights, i.e., the scope of equivalents, can be established.

Note that the above statements are based on the author’s considerations as part of the Essential Elements Review Committee and do not represent all matters discussed in the committee. They include the author’s personal opinions.