One of the pillars of European divisional practice is that, unlike e.g. US continuation-in-part applications, European divisional applications cannot contain any subject-matter which is not already contained in the parent application. Thus, each part of a European divisional application is entitled to the same filing date of the parent application.

The drawback of the European system may be that this system does not allow for the inclusion of additional developments in the divisional application in such a way as to enjoy, for such additional developments, a later filing date and thus a later expiry date. However, this system normally presents the advantage of knowing that, in any case, a parent application cannot be cited as prior art against its own divisional application, and vice versa.

However, there are exceptions even to this (unwritten) rule.

In a very recent decision of the EPO Boards of Appeal, rendered on September 12, 2012, the Board found that a divisional application could in fact form part of the state of the art of its own parent patent, and while at that even have a novelty-destroying effect on one of the parent claims.

In this case, the parent patent and the divisional application both claimed priority from an earlier application. In normal circumstances, the priority claim would be valid for both the parent patent and the divisional application, so that neither could be cited against the other.

However, in this case the Board found that one of the independent claims of the parent patent under review in the appeal proceedings (claim 1) was not entitled to the priority date since the priority document only disclosed a subclass of the embodiments covered by that claim. As a result, that claim of the parent patent was only entitled to its filing date. On the other hand, the divisional application, which disclosed the subclass in question, was entitled to the priority date. This led the divisional application to qualify, with respect to the parent claim 1, as a European application published after the prior art cutoff date of that claim (i.e. the filing date) but claiming a priority date falling earlier than that cutoff date. According to the EPC terminology, the divisional application was thus an intermediate prior art document for parent claim 1, i.e. a prior art document that could not be relied upon for assessing the inventive merit of that claim, but surely could be relied upon for assessing its novelty.

Since the divisional application disclosed a subclass of the embodiments covered by parent claim 1, and in application of the rule whereby the species is novelty-destroying for the genus, the disclosure of the divisional application was found to be novelty-destroying for parent claim 1.

In the end, the parent patent was maintained as claim 1 was limited so as to cover only subject-matter entitled to the priority claim, thereby excluding the divisional application from the state of the art citable against such amended claim.

So what does this case teach? Once again, it teaches that the EPO applies a rather strict approach when assessing the validity of priority claims. Thus, while drafting a European application claiming priority from earlier applications so as to include the further subject-matter developed in the course of the priority year is certainly wise with a view to helping the applicant obtain protection for such further subject-matter as well, it is fundamentally important to carefully assess the subject-matter to be included in any divisional applications. Indeed, a proper choice of that subject-matter can help avoid such self-colliding situations and thus obtain the whole protection deserved by the applicant.

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