R. 76(1) EPC (former Art. 99(1) EPC 1973) provides, inter alia, that "notice of opposition shall be filed in a written reasoned statement". R. 76(2)(c) EPC (former R. 55(c) EPC 1973) requires the notice of opposition to contain, inter alia, "a statement of the extent to which the European patent is opposed". Opposition proceedings constitute an exception to the general rule under the EPC that a European patent after grant is no longer within the competence of the EPO but becomes a bundle of patents within the jurisdiction of the designated contracting states. Opposition proceedings are an exceptional procedure whereby, during a limited period of time, a centralised action for revocation of a European patent may be brought before and decided by the EPO.
The case law of the boards of appeal had for some time been divided on the extent to which the opposition division or a board of appeal could examine the patent in accordance with Art. 101 and 102 EPC 1973 (now merged in R. 101 EPC). Some boards had advocated that examination be restricted to the contested claims (e.g. T 9/87, OJ 1989, 438 and T 192/88). Others had favoured unrestricted examination of the grounds for opposition and the claims in accordance with Art. 114(1) EPC (e.g. T 156/84, OJ 1988, 372; T 266/87, T 197/88, OJ 1989, 412; T 493/88, OJ 1991, 380 and T 392/89).
In G 9/91 and G 10/91 (OJ 1993, 408 and 420) the Enlarged Board clarified that the examination of an opposition is limited to the extent to which the patent is opposed in the notice of opposition. However, this principle is subject to a restriction: even if the opposition is expressly directed only against the subject-matter of an independent claim in a European patent, claims which depend on any such independent claim can nonetheless also be examined as to their patentability if the independent claim is eliminated in opposition or appeal proceedings, provided that the validity of these dependent claims is put in doubt prima facie by the information which is already available (cf. also T 443/93, T 31/08; the principles set out in G 9/91 were followed by subsequent case law, e.g. T 1019/92, T 1066/92, T 1350/09).
The statements in the notice of opposition relevant to the extent to which the European patent is opposed should be interpreted in such a way that an addressee would understand them, taking into account the surrounding circumstances. However, the general practice to interpret the absence of such statements as an indication of the opponent's intention to oppose the patent concerned in its entirety, has been subject to scrutiny in the light of G 9/91. In the extreme case where the extent to which a patent is opposed is seriously questioned, such “liberal” practice might lead to a rejection of the opposition as inadmissible (T 376/90, OJ 1994, 906; see also T 1/88, in which the board based its interpretation of equivocal procedural acts on the "objective value of the explanation").
In T 114/95 the board held that if an opponent requested revocation of the patent in its entirety, it was sufficient to substantiate the ground(s) for opposition in respect of at least one claim of the patent for the requirements of R. 76(2)(c) EPC (former R. 55(c) EPC 1973) to be met (see T 926/93, OJ 1997, 447; T 1180/97, T 1900/07). R. 76(2)(c) EPC (former R. 55(c) EPC 1973) did not refer to claims but rather required that the notice of opposition should contain a statement of the extent to which the patent was opposed.