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European Practice: Is there risk in dividing a claim into two-part form? How useful is it to cite prior art in a patent application?

Date: 19 January 2022

It is a requirement of the European Patent Convention (EPC) that a description for a patent application should indicate the background art which, as far as is known to the applicant, can be regarded as useful to understand the invention (Rule 42(1)(b) EPC). The application should, “preferably, cite the documents reflecting such art”. Generally speaking there is no downside to adding to the description references to documents cited in the search report, but there are pitfalls if not done correctly.


Similar pitfalls are present when separating a claim into two-part form. This is a requirement of the EPC “wherever appropriate” and if the applicant does not separate the claim, the Examiner may do so in the text intended for grant. We therefore consider both of these issues in turn.


Prior art acknowledged in the description


Construction in the light of prior art - Validating construction, Purposive construction and Doctrine of Equivalents


Different forms of construction may be used in interpreting a claim. One possible choice is the so-called “validating construction” – i.e. the interpretation that gives validity to the claim. This has been recognized in UK case law for over a hundred years starting with Parkinson v Simon [1895] 12 RPC 403, in a time when opportunities to amend a patent were limited and courts would interpret patent claims to give them validity, just as they would notionally amend a contract to give it validity. The principle continued through to Beloit v Valmet [1995] RPC 705, but Jacob J (as he then was) said courts should not construe claims more broadly or narrowly in the light of prior art, but that when considering purposive construction, a claim may be construed purposively so as not to include within its scope the disclosure of prior art acknowledged in the patent. This is because “it can hardly have been the inventor’s purpose to cover that which he expressly recognises was old”.


Following Actavis v Eli Lilly [2017] UKSC 48, this principle might now be applied in the UK to the doctrine of equivalents.


Effect on construction of acknowledging the state of the art


In Germany, where validity and infringement are considered separately, the cited prior art has been known to help a proprietor to fend off a novelty attack: X ZR 16/17, Scheinwerferbelüftungssystem, 27 November 2018 (nullity case, EP 764811 B1), Headnote “When interpreting a patent claim, it must be taken into account that a patent seeks to distinguish itself with its teaching from the prior art described in it. If in the description a known prior art is equated with the preamble of a patent claim, the features of the characterising portion are, in case of doubt, not to be understood as being found in the prior art from which they are intended to be distinguished.”


In this case, the fact that the features of the preamble were in the cited prior art was not in dispute. To the contrary, this was helpful for the proprietor as this led to a narrower construction of the features in the characterising portion such that a novelty attack was unsuccessful. Only prior art cited in the patent is relevant in this regard, whereas the prosecution history is usually ignored by German infringement courts (German Supreme Court, judgment of 12 March 2002, X ZR 43/01 Plastic pipe part.)


We turn now to the somewhat trickier situation where there may be a dispute as to whether the prior art is correctly acknowledged in the description. In the particular example discussed the description referred to the preamble of the claim as representing the relevant prior art: Referring to UK case law, Storage v Hitachi [2003] EWCA Civ 1155, the following sentence was added to the description of the patent in the course of prosecution: “We acknowledge the disclosure in EP-A- 0156724 and US-A-4849929 of a storage device system in the form of a fault-tolerant Winchester type disk system, having the features of the pre-characterising portion of Claim 1 below.”



A question arose over whether the document EP 0156724 A1 (referred to as “Timsit”) was a valid starting point for inventive step analysis. It was held that the acknowledgement that Timsit disclosed the pre-characterising portion of Claim 1 would have led the skilled person to realise those features were not new, so the question of obviousness could be decided starting from the known features.


Finally, we turn to a German infringement case in which an acknowledgement of the cited prior art was relevant to a question of literal infringement. The case is X ZR 74/14, Luftkappensystem (“Air cap system”), 13 October 2015.


The case related to a paint sprayer (EP 0596939 B1), where the nozzle was constructed such that the air was sent into a first passage in a switched-on state for spraying paint, and into a second passage (so that the air leaves the system without interacting with the paint) in a switched-off state when the first passage was not to be used. The advantage over the prior art (which disclosed simply blocking the first passage) was that the back pressure is relieved and thus the air supply is put under lower stress and thus less likely to overheat (even without a special overpressure valve). The main claim related to blocking a passage and permitting air to flow through the other. The proprietor wanted “blocking” to be construed to include both full blocking and partial blocking of air flow. The description of the patent only mentioned “blocking” as such, but it was also clear from the description that partial blocking of air flow would be sufficient to achieve the desired effect.


The background section of the description used the term “restricted” in addition to the term “blocked” to describe prior art, but did not further distinguish between “blocked” and “restricted”. While the Appeal Court considered the use of the additional term “restricted” as highly relevant for the interpretation of “blocking” and interpreted the term “blocking” in the main claim as “full blocking”, the German Supreme Court overruled the decision of the Appeal Court and interpreted “blocking” as encompassing both, “full blocking” and “partial blocking”.


The reasoning for the overruling was because the description of the patent contained no teaching that the use of the different terms “blocking” and “restricting” would be of any relevance. In line therewith, the headnote of the German Supreme Court’s decision X ZR 74/14, Luftkappensystem (“Air cap system”) reads as follows: “If, in a patent specification, two measures that differ only in degree (here: blocking and restriction of an air flow) are named without detailed differentiation as the starting point for a problem arising in the state of the art, then it cannot without further justification be concluded from the fact that only the measure with the stronger effect (here: blocking) is mentioned in the patent claim that the measure with weaker effect is not sufficient to embody the protected teaching.”


This judgment is also in line with the established case law that when the description suggests two or more alternatives but only one of them appears in the claim, then all others are considered not part of the claimed invention and even ruled out as an equivalent means (German Supreme Court, judgment of 10 May 2011, X Z R 16/09 Occlusion device.) This distinction is not relevant in this case because the two terms “blocking” and “restricting” refer to different degrees of the same measure, rather than alternatives.


Moreover, the broad construction of the claims was based on the lack of a distinction between the terms “blocking” and “restricting”, rather than on the fact that they were used to describe prior art. The decision therefore shows that claim construction can be influenced by the definitions and the usage of the terms in the entire patent specification, which includes the background section.


Two-part form


Rule 43 EPC requires that, where appropriate, each independent claim of a patent application shall have: as a preamble, a statement of “those technical features which are necessary for the definition of the claimed subject-matter but which, in combination, are part of the prior art”; and a characterising portion, “specifying the technical features for which, in combination with the [aforesaid] features, protection is sought”.


According to the Guidelines for Examination in the European Patent Office (EPO), two part form is considered appropriate if it is clear that the invention resides in a distinct improvement in an old combination of parts or steps (Guidelines for Examination, F-IV, 2.3). We have had instances where Examiners have threatened refusal if this requirement is not met, but it is most unusual. These days, most examiners take a pragmatic approach and accept a reasoned excuse for not separating into two-part form, if that is the applicant’s preference.


The Guidelines give instances in which the two-part form is not suitable. In general, it is to be avoided if it would give a distorted or misleading picture of the invention or the prior art. Examples are: (i) a combination of known integers of equal status, the inventive step lying solely in the combination; (ii) modification of, as distinct from addition to, a known chemical process e.g. by omitting one substance or substituting one substance for another; and (iii) a complex system of functionally interrelated parts, the inventive step concerning changes in several of these or in their interrelationships.


A distorted or misleading picture arises where the separation into two-part form does not truly reflect the starting point for inventive step analysis. Courts are aware that inventive step must be analysed regardless of the characterisation of the claim (i.e. the words “characterised in that" should, in effect be ignored), but human nature being what it is, it is often difficult to ignore the applicant’s choice of separation of a claim and, as we will see, there are occasions where it may not be ignored.


The same rules of interpretation apply to both parts of the claim


The German Supreme Court, the Bundesgerichtshof, states quite consistently that both in the examination of patentability and in the examination of patent infringement, it is irrelevant whether a feature is in the preamble or the characterising portion.


There is no suggestion, for example, that the doctrine of equivalents is applied differently according to which part of the claim is under consideration – see the four German example cases listed in the box.





Generally speaking, prior art should be cited only where necessary. When citing prior art at all, it is better to be somewhat superficial and not mention too many features, to avoid anything that gives rise to a narrow construction of terms in the claims.


When drafting the description, one should include broad definitions of the terms used in the claims to be on the safe side such as “blocking shall comprise full and partial blocking” (see the above Air Cap System case). In this context, it may be helpful to try establishing at least two levels of abstraction. In the Air Cap System case, it would have further helped the proprietor simply stating in the description that blocking also encompasses partial blocking such as restricting.


In the description, one might want to avoid any language that tells the reader what not to do.


A European patent application will often not proceed to grant unless its independent claims are drafted in two-part form.


There is no formal distinction between the interpretation of the preamble and the characterising portion of a claim in the German courts. Care should however be taken to ensure accuracy in view of the psychological effect on interpretation the separation of a claim might bring.