For the past few years there has been fear that the law on priority claims in the European Patent Office (EPO) could result in a divisional application becoming prior art against its parent if the divisional application described subject matter that was clearly disclosed in an application from which its parent claimed priority, yet the parent itself had claims that were not entitled to such priority. An example might be a PCT application that claimed priority from a US application but contained added subject matter, where after regional phase entry in the EPO, a divisional application was filed. The divisional focused on the subject matter of the original US application, but the parent contained claims that were generic to both the subject matter of the original US application and the subject matter added in the PCT application. Such generic claims were only entitled to the date of the PCT application whereas the divisional was entitled to the date of the US application. As a result, the divisional could be considered as unpublished prior art under Article 54(3) of the European patent Convention. Such a scenario came to be referred to as the “poisonous divisional” and was played out in Decision T476/09. However, in other cases, boards of appeal found ways to avoid coming to this conclusion. The divergent lines of cases made it appropriate for a decision of the Enlarged Board of Appeal. This has now occurred in Decision G1/15 which was released to the public on February 1, 2017 and in effect destroyed, or severely limited, the effects of the “poisonous divisional” theory.
Article 88(2) of the European Patent Convention states:
“multiple priorities may be claimed in respect of a European patent application, notwithstanding the fact that they originated in different countries. Where appropriate, multiple priorities may be claimed for any one claim.”
An earlier decision of the Enlarged Board of Appeal (G2/98) had held that:
“use of a generic term or formula in a claim for which multiple priorities are claimed .. is perfectly acceptable … provided that it gives rise to the claiming of a limited number of clearly defined alternative subject matters.”
As has been the case in a number of other decisions of the Enlarged Board, it was concerned to ensure that applicants should not secure protection for inventions that had not yet been made at the time when the application in question was filed, noting that priority claims could only be made for the “same invention” as that disclosed in the priority application and that:
The requirement for claiming priority of the “same invention,” means that priority of a previous application in respect of a claim in an European patent application is to be acknowledged only if the skilled person can derive the subject-matter of the claim directly and unambiguously, using common general knowledge, from the previous application as a whole.
Hence, the decision’s concern that to claim multiple dates for a single claim, the claim must set out clearly defined alternative subject matters.
In its latest decision, the Enlarged Board went back to first principles, noting that under the Vienna Convention on the Law of Treaties, the legislative intent of a treaty (such as the European Patent Convention) as set out in the documents preparatory to the treaty (the tavaux préparatoires) should prevail over any case law interpreting the treaty. The Enlarged Board concluded that since the EPC is “a special agreement within the meaning of the Paris Convention,” the legislative intent of the sections of the EPC relating to priority claims had been to give effect to the priority provisions of Article 4 of the Paris Convention and that discussions prior to the adoption of the EPC on the meaning of those provisions of the Paris Convention were therefore a guide as to how the priority provisions of the EPC were to be interpreted. Based on this foundation, the Enlarged Board stated:
“It can thus be concluded both from the law and from the logic of the underlying concept that the right of priority as established in the EPC (and the Paris Convention) operates to exclude the collision of subject matter disclosed during the priority period with identical subject matter disclosed in a priority document, in so far as priority has been validly claimed.”
This being the case, the requirement of decision G2/98 that a claim could only have multiple priority dates if it claimed a limited number of clearly defined alternative subject matters “cannot be construed as implying a further limitation on the right of priority.” The proper test to be applied is described as follows:
In assessing whether a subject matter within a generic claim may enjoy partial priority, the first step is to determine the subject matter disclosed in the priority document that is relevant, i.e. relevant in respect of prior art disclosed in the priority interval. This is done in accordance with the disclosure test laid down in the conclusion on G2/98 and on the basis of explanations put forward by the applicant or patent proprietor to support its claim to priority in order to show what the skilled person would have been able to derive from the priority document. The next step is to examine whether the subject matter is encompassed by the claim of the application or patent claiming said priority. If the answer is yes, the claim is de facto divided into two parts, the first corresponding to the invention disclosed directly and unambiguously in the priority document, the second being the remaining part of the subsequent generic… claim not enjoying priority…
In order to be able to ascribe different dates to different parts of a claim therefore, it is sufficient that one can determine what subject matter comprised within the claim is disclosed in the priority document, for which the date of filing of this document is the relevant date and the rest of the claim has the date of filing of the European application (or in the case of a PCT application, the date of filing the PCT application) irrespective of whether the subject matter for which priority is recognized forms any “clearly defined alternative subject matter.” This being the case, there is no “poisonous divisional” because that part of the subject matter of the parent claim that was disclosed in the priority application will have the same effective date as any divisional directed specifically to subject matter disclosed in the priority document.