G1/15: an antidote to poisonous priority and toxic divisionals

To qualify for a right of priority a European patent application must be filed in respect of the same invention as the earlier application. ‘Partial priority’ refers to a situation in which only part of the subject matter encompassed by a claim is entitled to the priority date. Partial priority can arise where the priority document discloses a feature A and the subsequent application has been broadened to include alternative feature B. In such a case a claim directed to A or B (an ‘OR’-claim) will be entitled to the priority date for part A of the claim and the filing date for part B of the claim.

The situation is less straightforward when a generic term C is used to encompass features A and B (a generic ‘OR’-claim). Such a situation can occur for example by the broadening of a chemical formula, of a range of values or of chemical compositions relative to the disclosure of a priority document. The Enlarged Board of Appeal has previously considered such a situation in G2/98 and had held that partial priority was allowed for a generic term or formula in a claim “provided that it gives rise to the claiming of a limited number of clearly defined alternative subject matters”. Following on from this decision two diverging lines of case law have arisen with some decisions taking a generous approach to partial priority and others applying a much stricter approach.

One illustrative example of the strict approach is case T 476/09 relating to a priority document disclosing a range of ‘0.94 to 0.99’ which had been broadened to ‘0.930 to 0.990’ in the claims of the application. In this case it was held that the claimed range represented a continuum of a numerical range of values which did not correspond to distinctive alternative embodiments. The board did not acknowledge the presence of partial priority.

It is the strict approach that has led to the problem of ‘poisonous priority’ and ‘toxic divisionals’. ‘Poisonous priority’ is a term used when a priority document can become novelty destroying for a subsequent priority claiming application and ‘toxic divisional’ is the term used when a divisional application becomes novelty destroying for its own parent (or vice-versa).

Poisonous priority could occur where the priority document is an earlier European application which has been allowed to publish and where the claims of the later European application use a generic term which has been broadened relative to the priority document. Under the strict approach the claims of the later application are not entitled to the priority date and instead have an effective date of the date of filing. The published priority document therefore represents novelty only prior art (Article 54(3) EPC) for the claim of the later application and can ‘poison’ that application by anticipating the broader generic claim.

Similarly in relation to toxic divisionals, a divisional application discloses subject matter entitled to priority. The parent application includes a broadened generic claim which encompasses the narrower subject matter disclosed in the divisional application, but which under the strict approach is not entitled to priority. As a result, the divisional application could be considered novelty destroying prior# art against the parent application. In contrast a number of other decisions have taken a generous approach and acknowledged partial priority in comparable circumstances to those of T 476/09. For example in T 135/01, claim 1 was directed to a method for driving an electric motor involving first and second current switching steps, whereby the switching interval was defined as being in the range of ¼ < ô < ¾. In assigning priority, the claim was split up into a notional part specifying ‘approximately ô/2’ which was entitled to priority and a second notional part specifying the range of ¼ < ô < ¾ punctured by the range of ‘approximately ô/2’ which was only entitled to the date of filing. Accordingly, the board acknowledged partial priority for the narrower range disclosed in the priority document and encompassed within the broadened generic range of claim 1.

In view of the diverging case law, several questions were referred to the Enlarged Board which was effectively asked to decide between these two approaches. In the case underlying the referral, the Opposition Division had revoked a patent, which was based on a divisional application, based on a lack of novelty in view of the published parent application.

The referral has generated a lot of interest, with over 30 amicus curiae briefs received. In addition, the President of the EPO allowed proceedings before the examining and opposition divisions to be stayed in cases where the decision from these divisions depended entirely on the outcome of G 1/15.

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 Enlarged Board answered this question in the negative, stating ‘Under the EPC, entitlement to partial priority may not be refused for a claim encompassing alternative subject matter by virtue of one or more generic expressions or otherwise (generic ‘OR’-claim) provided that said alternative subject matter has been disclosed for the first time, directly, or at least implicitly, unambiguously and in an enabling manner in the priority document. No other substantive conditions or limitations apply in this respect.’

In relation to the proviso set out in G2/98, the Enlarged Board stated that it ‘cannot be construed as implying a further limitation of the right of priority’.

The decision also sets out a guide for assessing whether subject matter in a generic ‘OR’-claim may benefit from partial priority:

1. determine the subject matter disclosed in the priority document that is relevant, i.e. relevant in respect of the prior art disclosed in the priority interval; and
2. examine whether this subject matter is encompassed by the claim of the application or patent claiming said priority.

If the outcome of the second step is that the subject matter is encompassed, then the claim is conceptually divided into two parts. The first part corresponding to the invention disclosed directly and unambiguously in the priority document. The second part corresponding to the remaining part of the generic ‘OR’ – claim not enjoying priority but itself giving rise to the right of priority.

In coming to this conclusion, the Enlarged Board dismissed arguments that such an analysis creates uncertainty for third parties, acknowledging that ‘although it can be a demanding intellectual exercise, the decisions reached in T 665/0, T 135/01, T 571/10 and T1222/11 all show that it can be carried out without the need for any additional tests or steps’.

The new guidance clarifies the EPOs approach to the assessment of partial priority. In favouring the more generous approach, G1/15 sweeps away the additional limitations introduced by G2/98 requiring that claims must relate to ‘a limited number of clearly defined ‘alternative subject matters’. This should make it easier for applicants who top-up the disclosure made in the priority document based on developments made in the priority year to benefit from partial priority. While the issue of self-collision via so-called ‘poisonous priority’ and ‘toxic divisionals’ is not specifically discussed by the Enlarged Board, it seems that by endorsing the generous approach to partial priority the problem disappears.