In G 10/91 (OJ 1993, 420) the Enlarged Board held that in principle, the opposition division shall examine only such grounds for opposition, which have been properly submitted and substantiated in accordance with Art. 99(1) EPC 1973 in conjunction with R. 55(c) EPC 1973. Exceptionally, the Opposition Division may in application of Art. 114(1) EPC consider other grounds for opposition, which, prima facie, in whole or in part would seem to prejudice the maintenance of the European patent (see also the summary of G 10/91 in this chapter IV.C.3.3. above). This exercise of discretion by the opposition division is reviewed by the boards in accordance with G 7/93 (see e.g. T 1005/14).

In G 1/95 and G 7/95 ("Fresh grounds for opposition", OJ 1996, 615 and 626; consolidated proceedings), the Enlarged Board first defined the meaning of "grounds for opposition" within the framework of Art. 100 EPC, and paragraph (a) in particular, as well as in the light of G 10/91 (OJ 1993, 408 and 420 – see also summary of G 10/91 in this chapter IV.C.3.3.). It noted that the function of Art. 100 EPC is to provide a limited number of legal bases i.e. a limited number of objections, on which an opposition can be based, all "grounds for opposition" in Art. 100 EPC having their counterparts in other articles of the EPC which have to be met during the procedure up to grant. Whereas the grounds in Art. 100(b) EPC and 100(c) EPC each relate to a separate and clearly delimited legal basis for an opposition, the totality of the articles (Art. 52 to 57 EPC) within the meaning of Art. 100(a) EPC constitute a collection of different objections to the maintenance of the patent.

The Enlarged Board had, in G 10/91, explained that, in application of Art. 114(1) EPC, an opposition division may introduce a ground for opposition not covered by the notice for opposition, either of its own motion or upon application by an opponent, if such a ground is considered sufficiently relevant. If an opposition division does introduce such a ground into the proceedings before it, it will of course decide whether such ground prejudices the maintenance of the patent, in the decision that it issues. The Enlarged Board in G 10/91 had first used the term "a fresh ground for opposition" in the context of considering the proper application of Art. 114(1) EPC during opposition appeal proceedings, and the term as used there must be interpreted as intended to refer to a new legal basis for objecting to the maintenance of the patent, which was neither raised and substantiated in the notice of opposition nor introduced by the opposition division.

In G 1/95 (OJ 1996, 615), the Enlarged Board went on to hold that, in a case where a patent had been opposed on the grounds set out in Art. 100(a) EPC, but the opposition had only been substantiated on the grounds of lack of novelty and lack of inventive step, the ground of unpatentable subject‑matter based on Art. 52(1) and (2) EPC was a fresh ground for opposition and accordingly could not be introduced into the appeal proceedings without the agreement of the patentee.

In G 7/95 (OJ 1996, 626), it was held that in a case where a patent had been opposed under Art. 100(a) EPC on the ground that the claims lacked an inventive step in view of documents cited in the notice of opposition, the ground of lack of novelty vis-à-vis the said documents based on Art. 52(1) and Art. 54 EPC was a fresh ground for opposition and accordingly could not be introduced into the appeal proceedings without the agreement of the patentee. However, the allegation that the claims lacked novelty in view of the closest prior art document could be considered in the context of deciding on the ground of lack of inventive step.

In T 13/15 the board noted that, when deciding whether to admit a new ground for opposition, the criterion of prima facie relevance had to be applied by the opposition division (see G 9/91). However, there was no obligation for an opposition division to apply the principle of prima facie relevance in case of a new line of attack which was within the framework of a ground for opposition and which was based on a document which was already in the proceedings.

In T 1340/15 the appellant argued that "prima facie" was to be understood as "at first glance" and that the legal question of whether or not the granted claims were covered by the original disclosure of the application (Art. 100(c) EPC) could not be solved prima facie. The board considered that following G 10/91 the opposition division only had to determine if there were, prima facie, clear reasons for considering the issue of added matter. The "prima facie" test was not to be interpreted so narrowly as to mean that it must be possible to definitely conclude "at first glance" that Art. 123(2) EPC was actually infringed. In the case at hand, in view of the evident ambiguity of the language of the relevant passage, the opposition division had a valid reason for admitting the new ground.

According to the board in T 514/04, the lack of novelty objection originally raised against claim 5, relating to a process for the preparation of a product, did not extend to the products obtained from this process, including the products of claims 1 to 4, and that consequently the lack of novelty objection raised against claims 1 to 4 for the first time before the board was a fresh ground for opposition.

In T 1959/09 the patentee (respondent) had requested the board to refer to the Enlarged Board of Appeal the question whether an existing ground for opposition raised in respect of a different independent claim amounts to a fresh ground of opposition as set out in G 10/91. In this respect, reference was made to T 514/04 (see above), where the board had stated that the extent and ground for opposition mentioned in R. 55(c) EPC 1973 (R. 76(2)(c) EPC) were connected in the sense that a specific claim(s) is/are objected to under a specific ground or grounds. The patentee argued that it was inadmissible without the approval of the patentee to extend the opposition over and above this basic concept which defined both the extent to which the patent was originally opposed (cf. G 9/91) and the grounds originally submitted with respect to subject-matter opposed under Art. 99 (1) EPC and R. 55(c) EPC 1973 (cf. G 10/91). The board did not recognise the necessity for such a referral since the ground for opposition pursuant to Art. 100(c) EPC as well as the question whether the requirements of Art. 123(2) EPC were met were clearly considered in the impugned decision. In addition, the board distinguished the present case, where claims 1 and 17 of the main request both belonged to the same category and virtually included the same subject-matter, from the case in T 514/04, where the question posed was whether a ground for opposition raised against a claim to a process applied equally to a claim to a product produced by said process. Hence, T 514/04 had no bearing on the case at issue.

The board noted in passing that there was no basis in G 10/91 for the general assumption that a ground for opposition raised against an independent claim may not subsequently be raised by the opponent against another independent claim, falling within the scope of the opposition. According to the board, T 514/04 neither mentioned nor elucidated the relevant passages in G 10/91 which supported that assumption. Actually, G 10/91 appeared to regard a new ground for opposition as being a "ground for opposition not covered by the statement" pursuant to R. 55(c) EPC 1973, no indication being given in that decision which would justify the inference that this should be construed far more broadly as meaning any ground for opposition in respect of a specific given claim which was not covered by the statement pursuant to R. 55(c) EPC 1973 (R. 76(2)(c) EPC).