We previously reported the order of the Enlarged Board of Appeal in referral G1/15. The generous view of partial priority adopted by the Enlarged Board effectively neutralises the problem of “poisonous priority” and “poisonous divisional” applications in EPO proceedings. The full decision has now been published providing the reasoning behind the Enlarged Board’s conclusion.

Partial priority refers to the situation in which only some elements of a claim are entitled to the priority date. In G2/98 the Enlarged Board stated that partial priority was only allowed in claims where there are a limited number of clearly defined alternatives. Diverging lines of case law developed regarding claims in which there are multiple alternatives not spelled out as such in the claim, for example where the claim uses a generic term or Markush grouping. Some decisions reflected a generous approach to partial priority, based on whether the subject matter could be identified within what was claimed, while others were sceptical of granting partial priority to alternatives within a generic term that were not explicitly defined in the claim.

A clear approach was required, in particular, in view of the problem of self-collision where a priority application has a narrow disclosure and a subsequent priority-claiming application claims the invention more broadly. Under a strict interpretation of G2/98 the elements in the claims of the subsequent application that were also disclosed in the priority application may not be entitled to partial priority unless explicitly recited as alternatives. The narrow disclosure in the priority application, if it also publishes as a European application and becomes prior art under Art. 54(3) EPC, then destroys the novelty of the broader claims of the subsequent application. An analogous situation could occur with a divisional application.

The Enlarged Board was asked to answer the following question:

“1. Where a claim of a European patent application or patent encompasses alternative subject matters by virtue of one or more generic expressions or otherwise (generic “OR”-claim), may entitlement to partial priority be refused under the EPC for that claim in respect of alternative subject-matter disclosed (in an enabling manner) for the first time, directly, or at least implicitly, and unambiguously, in the priority document?”

The referral attracted a large number of amicus curiae submissions most of which argued in favour of a negative answer to question 1 as this would effectively neutralise the problem of self-collision.

The Enlarged Board analysed the provisions in the EPC and the Paris Convention relating to priority and came to the view that there are no other requirements for recognising the right of priority beyond “the same invention”, whether for single, multiple or partial priority. Thus, the “limited number of clearly defined alternatives” test from G2/98 according to the Board “cannot be construed as implying a further limitation of the right of priority.” The Board went on to outline a two-step test for assessing whether subject-matter in a claim with a generic term may enjoy partial priority:

  1. Determine the subject matter disclosed (under the EPO’s “directly and unambiguously” standard) in the priority document that is relevant in respect of prior art disclosed in the priority interval;
  2. Examine whether this subject matter is encompassed by the claim of the application or patent claiming priority.

If the result of the second step is that the subject matter is encompassed by the claim then the subject matter is entitled to partial priority. This is the case regardless of whether the subject matter is spelled out as an alternative in the claim. The Enlarged Board therefore answered question 1 in the negative endorsing a generous approach to partial priority based on a conceptual division of the claim.

The decision does not directly address the issue of “poisonous priority” and “poisonous divisional” applications by considering whether such a family member can be used in a prior art attack. However, by adopting a generous approach to partial priority the problem disappears. The subject matter in the priority or divisional application is then no longer “poisonous” because it shares the same priority date as the relevant elements of the claim.

The decision appears to provide legal certainty in confirming the conceptual approach. While the Board accept that the division of the claim may be “demanding” it does not require any additional steps or tests. The decision should also provide welcome relief for patent proprietors attempting to avoid the severe consequences of self-collision.