The U.S. Supreme Court on the Doctrine of Equivalents in Warner Jenkinson v. Hilton Davis

Intellectual Property Quarterly 1998, p. 149-164


The decision of the U.S. Supreme Court in Warner-Jenkinson, Inc. v. Hilton Davis Chemical Co.  has received a lot of attention in the United States because of the two issues that were addressed. First, the U.S. Supreme Court ruled on the existence and scope of the Doctrine of Equivalents under U.S. patent law [hereinafter also referred to as: the Doctrine]. The Doctrine of Equivalents allows for a scope of protection of a patent, which is not limited to what is covered by the language of the claims, but which also includes what is equivalent thereto. The second issue concerned the application of the Doctrine of Equivalents: is it a matter for the judge or the jury?  
This second issue is of paramount importance for patent litigation practice in the United States. However, this issue is of no relevance for the European situation, where patent cases are not tried before juries. Nevertheless, one cannot ignore that the matter was on the table in Hilton Davis, since it also played a role in the reasoning and opinions of the Supreme Court and the Federal Circuit Court of Appeals with regard to the Doctrine of Equivalents. 
The first issue, dealing with the existence and scope of the Doctrine of Equivalents are certainly of relevance for the European context. Article 69 of the European Patent Convention ("EPC") and the Protocol on the Interpretation thereof, require courts in the various European jurisdictions to apply a Doctrine of Equivalents, albeit within reason.  In determining the scope of that Doctrine, the national European courts should not so much apply their old, national doctrines, but should develop new and harmonized European criteria, instead. However, there is no possibility to appeal from any national decision to a European court with appellate jurisdiction. In addition, we see that national courts still render judgements, which are very much in line with their established national traditions, even if they are fully aware of decisions by other European courts in corresponding litigation. A telling example in this regard, are the different decisions by a number of national courts in the Epilady litigation.  
In such a set of circumstances, there seems little harm in looking at U.S. patent law for inspiration. Since 1982, the United States has a specialized appeals court with exclusive appellate jurisdiction in all patent matters: the Court of Appeals for the Federal Circuit. The decisions of that court are subject to (possible) review by the U.S. Supreme Court. Given the American legal tradition, this is a warranty for well-reasoned and detailed opinions (be it majority, dissenting or concurring opinions). In the U.S., the Doctrine of Equivalents goes back to the early 19th century. The U.S. is a jurisdiction with a common law tradition as is also the case in the United Kingdom. If one then bears in mind that the struggle under the European Patent Convention to find the right balance for a doctrine of equivalents is due, among others, to the circumstance that such a doctrine of equivalence was in essence non-existent in the United Kingdom , it certainly seems justified to take a closer look at Hilton Davis.

Judge or Jury?

As already mentioned, this issue is not of much relevance for the European situation. Nevertheless, one cannot ignore this matter for a proper evaluation of the opinions of the U.S. Supreme Court and the Federal Circuit. The experience in the U.S. is that a jury may conclude more easily that there is infringement of a patent ore even that a jury is even more likely to find against a foreign defendant.  Therefore, many a plaintiff prefers a jury trial, also because it increases the likelihood of (more) substantial damages being awarded. In recent years, verdicts of millions of dollars in patent matters were primarily issued by juries. In addition, a jury verdict can hardly be reversed on appeal, if there was at least a shred of evidence that justified the finding of the jury. The Federal Circuit Court of Appeals can only review the instruction of the jury by the trial court with regard to the legal criteria to be applied. However, the actual application by the jury of the legal criteria to the evidence remains a 'black box', which cannot be tested on appeal. All these circumstances have led to an increase of jury trials in patent matters in the United States. 
It is against this background that in 1996 the U.S. Supreme Court confirmed the ruling of the Federal Circuit Court of Appeals in Markman v. Westview, and did find that the interpretation of a patent claim is a 'matter of law', which is to be decided by the judge instead of the jury.   The Supreme Court argued that this safeguards a uniform interpretation of patent claims under the supervision of the Federal Circuit.
Within one year after this unanimous opinion, the Supreme Court had to address the question whether finding patent infringement under the Doctrine of Equivalents was a matter for the judge or for the jury. The Federal Circuit had found this to be a jury matter, but that court was strongly divided. After a hearing before a regular panel of three judges, the Federal Circuit decided to hear the case by the full court ('en banc') because of the importance of the issues at hand. A majority of the twelve judges found that applying the Doctrine of Equivalents was a factual matter, which is to be decided by a jury. This majority opinion was under severe criticism by five of the judges, who filed three dissenting opinions.  
Because of the major procedural implications of this matter, the U.S. patent community eagerly awaited the decision of the Supreme Court.  Although the parties to the litigation hardly addressed this matter in their briefs, a large number of third parties filed 'amicus briefs' with the Supreme Court, which briefs primarily dealt with the jury-issue.  Needless to say, that it was a major disappointment when the Supreme Court found that it did not have to decide this issue in this particular case and kindly declined the invitation.

Hilton Davis: The Existence of the Doctrine of Equivalents

One of the reasons for the Federal Circuit to hear the case 'en banc' probably was that this court had lacked consistency in dealing with the Doctrine of Equivalents by various panels of its judges. 
It is noteworthy that all twelve judges of the Federal Circuit expressly subscribed to the existence of the Doctrine of Equivalents, without any reservations. It is, however, with regard to the scope of the Doctrine and the criteria for its application that the court was divided. This resulted in a majority opinion, which was signed by six judges; one concurring opinion signed by one judge and three dissenting opinions to which five judges subscribed. In this context one should also bear in mind that it was primarily the judge-jury issue that played a substantial role in these dissenting opinions. For instance, Judge Plager took the position in his dissenting opinion that the Doctrine of Equivalence is an 'equitable doctrine' within the common law, so that as a consequence it belongs to the domain of a judge and not that of a jury. 
The fact that the Federal Circuit was so strongly divided certainly contributed to the decision of the U.S. Supreme Court to grant certiorari. That court also unanimously supported the existence of the Doctrine of Equivalents. Justice Thomas wrote on behalf of the Supreme Court: "Petitioner [...] invites us to speak the death of that doctrine.  We decline that invita¬tion." The Supreme Court issued a unanimous opinion  - with one concurring opinion by Justice Ginsburg, joined by Justice Kennedy, dealing with a minor issue which provided further guidance as to the application of the Doctrine. With regard to the actual test to be applied the "linguistic framework" the Supreme Court passed the ball back to the Federal Circuit. Nevertheless, the decision of the Supreme Court contains interesting opinions as to the scope and the foundations of the Doctrine, in particular against the background of the opinions as filed by the Federal Circuit.
It does seem remarkable that both the Federal Circuit and the U.S. Supreme Court are unanimous in their support of the Doctrine of Equivalents. In spite of the debate about the scope of the Doctrine, none of the 21 judges in the Supreme Court and the Federal Circuit, who ruled on the matter, disputed the rightful existence of the Doctrine.  
This unanimity of both panels underscores the long tradition of the Doctrine of Equivalents in the United States. As the Federal Circuit indicated in its majority opinion, the Doctrine can be traced back to precedents dating from the beginning of the last century, when two Circuit Court panels, in which two prominent Supreme Court Justices participated (as 'circuit judges' in a federal Circuit Court of Appeals) acknowledged the existence of the Doctrine.  In 1814 Justice Story, a leading intellectual property scholar at the time, subscribed to the Doctrine, finding that "mere colorable differences, or slight improvements, cannot shake the right of the original inventor".  In 1817 Justice Bushrod Washington came up with the 'triple identity'-test (also known as 'function-way-result'-test) to determine the substantiality of the differences between a patented product and the allegedly infringing device.  Thereafter, the U.S. Supreme Court has issued a number of opinions in which it subscribed to the Doctrine, starting with its Winans-decision of 1853 and ending, for the time being, with Graver Tank of 1950.   In Graver Tank the Supreme Court essentially found that the Doctrine of Equivalence is a necessity if the inventor is not to be placed at the mercy of verbalism and if substance is to prevail over form in patent matters.  
However, the strong division among the Federal Circuit judges pertaining to the scope of the Doctrine, illustrates that it is relatively easy to subscribe to the Doctrine of Equivalents as such, but that real problem is to define and justify its scope. There, a judge can choose from a large spectrum of possibilities, varying from rather strict to very liberal. This is exactly the problem that the various European jurisdictions have to tackle in their quest to find a 'common ground' under Article 69 of the European Patent Convention. It is for that reason that Hilton Davis may have something to offer to the European patent community.

Criticism on the Doctrine of Equivalents

The Doctrine of Equivalence has been critically reviewed in the past, among others in the dissenting opinions of Justice Black and Justice Douglas in the Graver Tank-decision of 1950. Neither of these two distinguished members of the Supreme Court rejected the Doctrine of Equivalents, but they criticized the scope of its application, which they thought to be too broad. In particular Justice Black did emphasize that patent law creates a limited exemption to the general principle of the freedom to compete. As a consequence, all that is not expressly claimed should be free for others to use.  He stressed that expanding the scope of protection outside the language of the claims is unjust towards third parties. In this context he referred to the earlier decision of the Supreme Court in White v. Dunbar, where the Court, for that reason, had said that one should not treat a claim as "a nose of wax which may be turned and twisted in any direction, by merely referring to the specification, so as to make it include something more than, or something different from, what its words express".   In Justice Black's judgement the language of the claims had been expanded too much in Graver Tank, also because of the possibility as it exists in the U.S. to have a patent reissued by the Patent Office, which makes it possible to correct claim language that turns out to be somewhat unfortunate. 
The dissenting opinions of the Federal Circuit in Hilton Davis also specifically addressed the difficulty of keeping the Doctrine of Equivalents within proper boundaries. For example, Judge Plager argued in his dissent that applying the Doctrine often times means that the owner of a patent gets protection for what is obviously outside the scope of the claims. The tests for the application of the Doctrine are not much more than a formulaic chant -- function, way, result which provide little in terms of specific guidance.   There are indeed no strong criteria for setting the outside boundaries of the Doctrine of Equivalents, which lack of clarity is indeed contrary to the public interest that requires reasonably clear lines of demarcation between what is protected by a patent and what is in the public domain.

All Elements Rule

The Supreme Court was receptive to these concerns of the dissenters in the Federal Circuit and, for that reason, adhered to the 'all elements rule' that was also advocated by the late Judge Nies of the Federal Circuit in her dissenting opinion to Hilton Davis.  Judge Nies underscored that the application of the Doctrine should not result in a scope of protection being granted that is broader than the claims as authorized by the Patent Office. She indicated that this will not be the case if in case an invention consists of a combination of a number of elements  - the test is not whether the product or process as a whole is equivalent to what is described in the claim, but whether equivalency exists with regard to each individual element thereof. The Supreme Court argued that this approach does justice to the weight that should be given to each element of a claim and that, for the same reason, an element of the claim should not be eliminated.
The 'all elements rule' as such is not new. It was already established in an earlier decision of the Federal Circuit. The Supreme Court's decision in Graver Tank of 1950 had left open whether equivalency was required for the invention taken as a whole or with regard to each individual element. In 1987 a small majority of the Federal Circuit (en banc) subscribed to the 'all element rule' in Pennwalt.  In subsequent cases, it was dependent upon the composition of the panel whether or not the Federal Circuit would actually apply the 'all elements rule'.   This reluctant introduction of the 'all elements rules' by the Federal Circuit in Pennwalt has now been promoted by the U.S. Supreme Court in Hilton Davis to be 'the law of the land'.
The invention of Hilton Davis, as described in U.S. Patent 4,560,746 of 1985 deals with a purification process of dye, where the improvement over the prior art is in  "subjecting an aqueous solution (...) to ultrafiltration through a membrane having a nominal pore diameter of 5-15 Angstroms under a hydrostatic pressure of approximately 200 to 400 p.s.i.g., at a pH from approximately 6.0 to 9.0 (...)".  In 1986 Warner-Jenkinson, unfamiliar with the invention of Hilton Davis, developed a similar process that used a pressure of 200 to 500 p.s.i.g. at a pH of 5.0. The phrase 'at a pH approximately 6.0 to 9.0' was used in the claims to distinguish the invention from an earlier patent, where a similar method was described using a pH above 9.0. It was unclear, however, why the claim also referred to a pH of 6.0 as a lowest level.
As a consequence of the 'all elements rule' this lowest level as set forth in the claim cannot be ignored, so that it needed to be established that a pH of 5.0 is equivalent to a pH of approximately 6.0. Since the Federal Circuit had not expressly ruled on that subject, the Supreme Court reversed and remanded for further proceedings on this issue. In the meantime the Federal Circuit has ruled on the subject in its decision of June 13, 1997 finding that there was substantial evidence to support the jury's verdict of equivalence.  This revision by the Federal Circuit of the 'black box' jury verdict was by its nature only marginal. 

Prosecution History Estoppel

Application of the Doctrine of Equivalency may also conflict with subject matter that the patentee expressly gave up in the course of the patent prosecution. If the patentee limited the text of the claim during the application process, it would of course be unjust if he would be able to reclaim that lost terrain under the Doctrine of Equivalence. The Supreme Court acknowledged this doctrine known as "prosecution history estoppel" or "file wrapper estoppel" as did the Federal Circuit. The Federal Circuit had found that a pH at 6.0 was introduced in the claim to circumvent a problem caused by the prior art or to otherwise give up possible protection.  Warner-Jenkinson argued that the reason for a particular limitation of the claim is immaterial, so that any narrowing of the claim would necessarily result in a more limited scope of protection. 
The Supreme Court considered that earlier case law on 'prosecution history estoppel' primarily dealt with situations where a limitation was brought into the claims to circumvent problematic prior art that stood in the way of the patent being granted. Therefore, the reason for the limitation was always at issue in those cases. The 'amicus brief' filed by the U.S. Patent and Trademark Office with the Supreme Court did indicate that there can be numerous reasons for amending a claim, so that a change in the text does not necessarily imply that the scope of the claim was meant to be limited.
In this particular case, it was unclear why the low level of a pH at approximately 6.0 was introduced in the claim. The Supreme Court found that it is reasonable (a) to put the burden of proof as to the reason for a certain change on the patent holder and (b) to assume that there was a substantial reason related to patentability for including a limiting element in a claim, if no explanation can be given. In that case 'prosecution history estoppel' will stand in the way of applying the Doctrine of Equivalence.   
This approach clearly places a risk with the patent holder, who probably more than before has to ask himself whether a particular change in the language of the claims may result in a more limited scope of protection. Thus, substantial weight is given to a careful drafting of the claims and a persistent defense of the required claim language vis-à-vis the examiner. If one bears in mind that patents do form an exception to 'the freedom to compete' and the 'freedom of technology'  and that therefore the interests of the public and/or (possible) competitors should be held 'in high regard', this approach seems justified to me.
The Supreme Court also considered that it is not up to a court in an infringement suit to investigate whether the grounds for a particular amendment of a claim were sound or not. Implied in the division of powers in the patent system is that a court has to take the end result of the patent application process as its point of departure. 
The other side of this coin is that the position of the applicant (and his counsel) has not been made easier. This may result in debates with the examiner becoming more rigid because the applicant may be more inclined to try to stick to the (probably broad) language used in the first draft of the claim in the original application. Justice Ginsburg also addressed such concerns in her concurring opinion by advocating leniency towards claims that were issued pre-Hilton Davis, since the patentee had no notice at the time of the patent prosecution that these presumptions would apply. Such a patentee may have been somewhat relaxed, consenting to a particular amendment of the claim language hoping that such might ease the granting of the patent but not (fully) anticipating that it might haunt him in this (severe) manner. Such carelessness which probably was never really justified - should certainly be a thing of the past after Hilton Davis.

Intent Defendant Irrelevant

In Graver Tank the Supreme Court had argued that one of the goals of the Doctrine of Equivalence was to stop the "unscrupulous copyist" and acts of piracy.  However, this does not imply that the Doctrine is only available in case of  'intent' by the infringer. Referring to Winans v. Denmead of 1854 and Machine Co. v. Murphy of 1878, the Supreme Court ruled in Hilton Davis that finding infringement under the Doctrine of Equivalence is essentially the same as determining what is identical to the patent, since equivalency requires that the differences are insubstantial.  Therefore, the Supreme Court found that just as intent is irrelevant in case of a literal infringement, intent does not play a role under the Doctrine of Equivalence.

Designing Around Versus Intentional Copying?

In Hilton Davis the Federal Circuit had found, while referring to Graver Tank, that intentional copying raised an inference of insubstantial differences while intentionally 'designing around' raised an inference of the opposite. The Supreme Court argued that this explanation 'leaves much to be desired', for instance, because it is unclear how one can ever distinguish between 'the intentional copyist' and the 'incremental innovator designing around the claims'. Nevertheless, the Supreme Court did attribute some meaning to the fact whether independent experimentation has taken place. It argued that the need for independent experimentation could reflect the lack of knowledge by one presumably skilled in the art as to the interchangeability of the allegedly infringing device and what is described in the claims and thus about the substantiality of the differences.  The Court's finding seems to contain some reservations in this regard. It seems to me that the reasons for and the scope and nature of any such experimentation can differ so dramatically that one should probably only see it as one of many circumstances that can be taken into consideration to determine whether or not the differences are substantial, without awarding any special status thereto.

Interchangeability in the Eyes of One Skilled in the Art at the Time of Infringement 

The Doctrine of Equivalency conflicts with the principle that competitors can educate themselves about the existence and scope of the rights of the patent holder and can thus develop or amend their policy. As Justice Black rightfully argued in his dissent in Graver Tank, any protection granted outside the scope of what is specifically claimed leads to uncertainty for third parties and deviates from the principle that what is not specifically claimed should be in the public domain.  However, uncertainty is a given in all legal exercises, so that we should not be too dramatic in this regard. However, it is certainly something to appreciate if we can find an objective standard and thus diminish the degree of uncertainty that may exist. The Supreme Court did find such an objective standard in "a skilled practitioner's knowledge of the interchangeability between claimed and accused elements".  This perspective of a skilled practitioner does not only provide content to the concept of 'equivalence' but at the same time provides its limits, according to the Supreme Court.  
On the basis of that finding, the Supreme Court saw no difficulty to determine that the Doctrine of Equivalence encompasses everything that is interchangeable in the eyes of one presumably skilled in the art at the time of the alleged infringement. The Supreme Court found no reason to limit the scope of the Doctrine to what is known to be interchangeable at the time of the grant of the patent or to what is actually disclosed in the patent itself. 
Taking the 'time of the infringement' to measure knowledge of interchangeability seems questionable to me. If one wants to subscribe to the notice-function of a patent it seems more reasonable to refer to what is known at the time of the patent being granted or the time at which the alleged infringer has (or should have) checked the patent register.  However, the actual implications of these nuances are probably too subtle to have any practical consequences.   It is probably more relevant to note that this approach by the Supreme Court does allow for a scope of protection, which is substantially broader than one could anticipate at the time that the application was evaluated or at the time that the patent was granted. 

Triple Identity (Function-Way-Result) Versus Insubstantial Differences?

After having set the stage in this manner, the question the Supreme Court still had to answer was what the 'linguistic framework' for determining equivalence should be.  
As already mentioned, in 1817 U.S. Supreme Court Justice Bushrod Washington as a judge in a trial court already applied the so-called 'triple identity' test: is there in essence the same function, way and result?  In 1950 the U.S. Supreme Court also applied the same test in Graver Tank. 
In Hilton Davis the Federal Circuit had found that the 'function-way-result-test' was not the (sole) test for finding equivalence and that Graver Tank also did not support such an approach. The Federal Circuit found that the 'triple-identity-test' had primarily been developed in an age of relatively simple mechanical technology, where in general - it has served its purpose and went on to argue that this test can no longer suffice where technology becomes more and more complex. That court then did rule that it should be decisive whether the differences between the patented and the allegedly infringing device are substantial ('substantial differences test'). In particular Judge Lourie in his dissent was critical of the 'function-way-result-test' ('FWR') and argued that it was insufficient. In particular in the field of chemistry, it may be wrong to deem a particular function to be relevant, while the claim is limited to a certain structure of a chemical compound. Substantially different and separately patentable structures can perform the same function in the same way, while there is no justification for finding infringement under the Doctrine of Equivalence, as Judge Lourie argued. 
In all the opinions of the Federal Circuit a lot of attention had been given to he issue as to whether the 'function-way-result'-test or the 'insubstantial differences'-test would be better. The U.S. Supreme Court also did find that the "function-way-result-test' may not provide the best means to determine equivalency in case of non-mechanical inventions. However, the 'insubstantial differences'-test does seem to provide little in terms of specific guidance as to what kind of differences should be considered to be substantial or insubstantial. In effect, one shifts the problem from having to define equivalence to having to define what is substantial.  
The Supreme Court did not come up with a definition of 'insubstantial' and referred this subject to the Federal Circuit to be further dealt with and developed on a case by case basis. The Supreme Court saw no purpose in micro managing the Federal Circuit's particular word choice for analyzing equivalence and left such refinement to that court's judgement in this area of its special expertise. In essence, this judgement of the Supreme Court is in line with the approach taken in the majority opinion of the Federal Circuit and demonstrates a sense of reality. If the 150 years of existence of the Doctrine of Equivalence has not resulted in a satisfactory and easily applicable 'linguistic framework', one may not have high hopes from an uninspired, forced effort. With this approach, the Supreme Court also followed the direction set in Graver Tank, where the court had found that equivalence should not be "the prisoner of a formula".   
The Supreme Court underscored that more important than the 'linguistic framework' is whether the test is probative of the essential inquiry, which is whether the accused product or process contains elements that are identical or equivalent to each claimed element of the patented invention. The Supreme Court therefore primarily relies on the 'all elements rule' for keeping the Doctrine of Equivalence within proper boundaries.


From a Netherlands, i.e., European perspective, a number of issues seem to be of particular relevance. 
First, the opinions of the U.S. Supreme Court and the Federal Circuit with regard to the foundation of the Doctrine of Equivalents and its scope, do seem to lend themselves for application in a Netherlands or European setting. The principles behind the Doctrine and the weight given to the public interest and certainty for third parties are fully within the scope of the Protocol on the Interpretation of Article 69 EPC.  This American case law on the Doctrine of Equivalence also seeks to determine a rightful balance between "a fair protection for the patentee" and "a reasonable certainty for third parties". The protection granted by a patent is also not limited to  "the strict, literal meaning of the wording used in the claims", and also clearly rejects a system in which "the claims only serve as a guideline". In short, this U.S. jurisprudence also wrestles with the same dilemmas and issues as the European jurisdictions that have to (indirectly) apply article 69 EPC. All the more reason therefore to look upon these American precedents as 'lessons learned'.     
In the U.S., the Doctrine of Equivalents can rely upon a tradition that goes back to the beginning of the last century. What is noteworthy against this background is that in spite of all the debates about the actual scope of its application, the existence of the Doctrine as such is not disputed (neither by the U.S. Supreme Court, nor by the Federal Circuit Court of Appeals).
It also seems of relevance that one does not regard the application of the Doctrine as something different from determining literal infringement. In Hilton Davis, the Supreme Court referred to Winans v. Denmead of 1854 and Machine Co. v. Murphy of 1878 and the concept set forth in those opinions that "in the eyes of the patent law" the patented inventions and its equivalents are identical.    
Determining equivalency is therefore not seen as an abstract exercise that allows for determining a scope of protection while paying little respect to the language of the claims. Equivalency does not mean that one abandons the language of the claims or that this language only functions as a guideline to determine the essence of the actual invention, which is then to be seen as the starting point for determining equivalence. Instead, the language of the claims remains of paramount importance and provides clear boundaries to the scope of protection that can be granted under the Doctrine of Equivalence.  
This starting position leads to the principle that equivalence can only be found if all elements of the patented invention are applied ('all elements rule'). In addition, it results in the principle that where a limiting element is included in the claims, one is to presume that the patent office had a substantial reason to include that element, albeit that this presumption is subject to rebuttal.   
All of this results in a scope of protection, which is rightfully broader than the literal meaning of the language of the claims. Nevertheless, it seems right to me that one has to keep close to the literal meaning of the claims (including all their elements and limitations) if one wants to do more than just pay lip service to 'a reasonable degree of certainty for third parties'. This scope of protection may be more limited than one would sometimes hope for, but it does seems fair that the holder of a patent has to live with the consequences of a claim, which is less than perfect. He has had a number of opportunities with professional assistance to make sure that the language of the claim would be as broad as rightfully possible. If one then keeps in mind that a patent constitutes an exception to the general principle of 'freedom of technology' , these basic assumptions do seem to find a just balance between the interests of the patent owner and those of competitors that have to be able to rely at least to some extents - on the language of the claims. 
It seems to me that this U.S. case law is right in sticking to the language of the claims as a point of departure and not taking the 'essence of the patented invention' as a guideline to determine the scope of protection, as for instance the Netherlands Supreme Court still seems to advocate. The doctrine of the 'essence of the patented invention' pays too little attention to the language of the claim and leads to a scope of protection that may bear little resemblance to the invention as described in the claims. This U.S. case law therefore supports those Netherlands scholars that have been critical of this Netherlands jurisprudence, being primarily Pieroen, who was in time supported by others like Brinkhof, Hamaker, Verkade and the Court of Appeals at The Hague.  It seems to me that the Netherlands Supreme Court should abandon this school of thought instead of paying homage to it as it keeps doing in recent opinions, such as those in Meyn v. Stork, Ciba Geigy v. Oté Optics and more recently in Stamicarbon v. Dow Chemical.   
 This U.S. case law also seems to provide support for the German case law, which teaches that the Doctrine of Equivalence stops where it is no longer clear to a skilled practitioner that the alleged equivalence is substantially the same as the invention described in the claims.  Put differently, if an inventive step is required to see the interchangeability there is no room for equivalence: equivalence stops where a new invention takes off.  This does not mean to say, however, that an infringement by means of equivalence cannot occur in case of a dependant patent: the situation where one does apply the patented invention (by means of equivalence), but at the same time has found a new, inventive construction or design.  If the claims describe a wheel as a general concept, one may have a dependent (and infringing) patent on a wheel with a rubber tier, even under the Doctrine of Equivalence. 
In view of the above, it seems to me that Hilton Davis and the preceding case law of the U.S. Supreme Court and the Federal Circuit Court of Appeals do constitute good sources of inspiration for the development of patent law in Europe. Of course, this does not mean that one can look upon the Federal Circuit and the U.S. Supreme Court as informal appellate courts in the context of the European Patent Convention. It does mean, however, that it is of importance to follow the developments in the U.S., perhaps more than before.  Any extended form of harmonization of patent laws can only be welcomed, since it results in more certainty for the global business community and thus serves the public good.