In T 118/91 and T 80/98, care was taken to avoid any risk of double patenting by ensuring that the subject-matter of the divisional application differed from that of the parent application. In T 118/91, in particular, the board stated that it could find nothing to support the contention that features forming part of the subject-matter of the divisional application could not be the subject of a dependent claim in the parent application. The board agreed with the Guidelines that, as a general rule, one application may claim its own subject-matter in combination with that of the other application. This approach does not lead to "double patenting" in its normal sense. In this particular case, the board was satisfied that any danger of "double patenting" had been eliminated by extensive restriction of the claims in the divisional application.

In T 587/98 (OJ 2000, 497) the examining division, relying on the Guidelines prohibiting "conflicting" claims, had refused a European patent application, filed as a divisional application, on the grounds that its subject-matter overlapped with that of the parent application and that in the overlapping region the same subject-matter was claimed; as legal basis for the refusal it invoked Art. 125 EPC. The board held that Art. 125 EPC was not applicable to the case at issue since this article required "the absence of procedural provisions in the Convention" but the provisions governing divisional applications were self-contained and complete. In addition a prohibition of "conflicting" claims in the wide sense applied by the examining division would be a matter of substantive law rather than a matter of procedure – and Art. 125 EPC was not applicable to substantive law. The board also found that there was no express or implicit provision in the EPC which prohibited the presence in a divisional application of an independent claim – explicitly or as a notional claim arrived at by partitioning of an actual claim into notional claims reciting explicit alternatives – which was related to an independent claim in the parent application (or patent, if it had already been granted) in such a way that the "parent" claim included all the features of the "divisional" claim combined with an additional feature.

In T 307/03 (OJ 2009, 422) the board understood T 587/98 to have found that there was no basis in the EPC prohibiting "conflicting claims" within the meaning of the guidelines; it could not follow T 587/98 on this point. The board in T 307/03 held that the principle of the prohibition of double patenting, namely that the inventor (or his successor in title) has a right to the grant of one and only one patent from the EPO for a particular invention as defined in a particular claim, can be deduced from Art. 60 EPC 1973. Once a patent had been granted, this right to a patent had been exhausted and the EPO was entitled to refuse to grant a further patent to the inventor or his successor in title for the subject-matter for which he had already been granted a patent. Furthermore, a double patenting objection can also be raised where the subject-matter of the granted claim is encompassed by the subject-matter of the claim later put forward, that is where the applicant is seeking to re-patent the subject-matter of the already granted patent claim, and in addition to obtain patent protection for the other subject-matter not claimed in the already granted patent. In particular, where the subject-matter which would be double patented is the preferred way of carrying out the invention both of the granted patent and of the pending application under consideration, the extent of double patenting cannot be ignored as de minimis. To avoid the objection of double patenting the claims of the pending application should be confined to other subject-matter that is not already patented. See however T 2402/10 (summarised below).

According to the board in T 1423/07, Art. 60 EPC provides no basis for refusing a European application for double patenting. The purpose of Art. 60 EPC is only to define to whom the right to a European patent belongs. Art. 60 EPC could not be interpreted such that the inventor or his successor in title had a right to the grant of one and only one patent from the EPO for a particular invention, with the consequence that claims comprising subject-matter included in the claims of an already granted patent of the same applicant were refused no matter whether or not the applicant had a legitimate interest in the grant of the subsequent application.

In T 1391/07 the board noted that the practice of prohibition of "double patenting" was confined to patents and applications relating to the same invention as defined by the subject-matter of the corresponding claims and therefore confined to claims conferring notionally the same scope of protection. It saw no basis for extending this practice to cover claims not defining the same subject-matter but conferring – as in the case before it – a scope of protection overlapping with each other only partially in the sense that some, but not all of the embodiments notionally encompassed by one of the claims would also be encompassed by the other one of the claims. In particular, the lack of legitimate interest of an applicant in obtaining two patents for the same subject-matter – as invoked by the Enlarged Board of Appeal in decisions G 1/05 date: 2007-06-28 (OJ 2008, 271) and G 1/06 (OJ 2008, 307) – cannot be invoked when the scopes of protection conferred by the respective subject-matters overlap only partially with each other as there is no manifest objective reason to deny the legitimate interest of the applicant in obtaining a protection different from – although partially overlapping with – that of the parent patent already granted. Accordingly, the board concluded that the mere fact that the scope of protection notionally conferred by the claim in suit would partially overlap with that of the granted parent patent did not prejudice the grant of a patent (see also T 587/98, OJ 2000, 497; T 877/06; T 1491/06; T 1780/12; T 2461/10; T 2563/11).

In T 2402/10 the respondent raised an objection of double patenting, since claim 1 had been amended during the opposition/appeal proceedings in such a manner that its scope fully encompassed the scope of the claims of the patent granted from the grand parent application. The board recalled the well-established case law that a principle of prohibition of double patenting existed on the basis that an applicant had no legitimate interest in proceedings leading to the grant of a second patent for the "same subject-matter" (G 1/05 date: 2007-06-28, OJ 2008, 271; G 1/06, OJ 2008, 307; see also T 1391/07, T 877/06, T 1708/06, T 469/03). In the case at issue, claim 1 contained technical features not required by any claim of the patent granted from the grant parent application. Since the patent granted from the grant parent application and the patent in suit claimed different subject-matter, the question of double patenting could not arise. The board noted that the respondent also referred to the headnote of T 307/03, according to which a double patenting objection could also be raised where subject-matter of the granted claim was encompassed by the subject-matter of the claim later put forward. The board, however, saw this as no reason to depart from the mandatory requirement of "same subject-matter" invoked in decisions G 1/05 date: 2007-06-28 and G 1/06 and in the established case law. See also T 1155/11.

In T 1766/13 the board held that, with respect to the case at issue, a product and a method for its manufacture were not "the same subject-matter" in the sense of G 1/05 date: 2007-06-28 and G 1/06. According to T 1765/13, the same was true for the use of a product and a method of fabricating it. For a further case where parent application and divisional application did not relate to the same subject-matter, see T 1708/06.

In T 1780/12 the board held that the category of a claim and its technical features constituted its subject-matter and determined the protection conferred (see G 2/88, OJ 1990, 93). The claims in question were of different categories: Swiss-type claims were purpose-limited process claims (Use of X for the manufacture of a medicament for the treatment of Y) and claims formulated in accordance with Art. 54(5) EPC were purpose-limited product claims (X for use in the treatment of Y). As regards the technical features, the board concluded that both sets of claims defined the same compound and the same therapeutic use, but that the Swiss-type claims comprised in addition the feature of manufacturing a medicament whereas the claim in accordance with Art. 54(5) EPC did not. The claimed subject-matter was thus different. The board also considered that the scope of protection was noticeably different. It was generally accepted as a principle underlying the EPC that a claim to a particular physical activity (e.g. method, process, use) conferred less protection than a claim to the physical entity per se (see decision G 2/88). It followed that a purpose-limited process claim also conferred less protection than a purpose-limited product claim. (See also T 879/12, T 13/14 and T 15/14 agreeing with the conclusions in T 1780/12.)

In T 2563/11, the appellants had contended that the prohibition on double patenting did not apply because, despite their identically worded independent claims, the parent patent and the divisional application had different descriptions and so each conferred a different extent of protection under Art. 69 EPC. The board observed that the important point for the purposes of the prohibition on double patenting was whether the "same subject-matter" was claimed. A claim's subject-matter was defined by its category and technical features (Art. 84 EPC and R. 43(1) EPC). The description was therefore irrelevant in establishing whether the same subject-matter was claimed, especially if the claims in question were anyway clear and understandable in themselves (see T 197/10). By contrast, while the claims were likewise the basis for determining the extent of protection conferred by a European patent, Art. 69(1) EPC provides that the description and drawings were to be used to interpret them for this purpose, and this meant that the extent of protection conferred by the patent might be broader than the subject-matter claimed. In the case in hand, the board rejected the appellants' contention that, owing to the considerable differences between the descriptions, claim 1 of the divisional application covered broader subject-matter than its equivalent in the parent application.