In G 3/97 and G 4/97 (OJ 1999, 245, 270) it was held that the legislator had expressly designed the opposition procedure as a legal remedy in the public interest, which under Art. 99(1) EPC was open to "any person". It is a principle firmly established by board of appeal case law that the admissibility of an opposition is examined by the EPO of its own motion. An objection that the opposition is inadmissible because the opponent is not entitled to file an opposition may be raised at any stage of the proceedings, i.e. even at a late stage before the board of appeal, because the admissibility of the opposition is an indispensable procedural requirement for any substantive examination of the opposition submissions (see T 289/91, OJ 1994, 649; T 28/93, T 590/94, T 522/94, OJ 1998, 421; T 960/95 and T 1180/97). If the board of appeal has good reasons for examining the admissibility of an opposition (T 199/92), it may and is obliged to do so, even if the patent proprietor has not challenged admissibility during either opposition or appeal proceedings (T 541/92). In G 4/97 (OJ 1999, 270), the Enlarged Board of Appeal reaffirmed that the admissibility of an opposition could be challenged during the appeal proceedings on grounds relating to the identity of an opponent, even if no such objection had been raised before the opposition division.
An opponent's status is a procedural status, and the way it is substantiated is a matter of procedural law (G 3/97 and G 4/97, OJ 1999, 245 and 270). This is laid down in Art. 99(1) EPC in conjunction with Art. 100 EPC 1973, R. 76 and R. 77(1) EPC (former R. 55 and R. 56(1) EPC 1973). According to those provisions, the opponent is the person who meets the conditions set out therein for filing an opposition, in particular that of identifiability. The EPC sets no other explicit formal conditions for opponents.
Moreover, the EPC does not require that the opponent have his own interest in the outcome of the opposition proceedings; Art. 99(1) EPC 1973 (substance unchanged) states that "any person" is entitled to file a notice of opposition. As early as in G 1/84 (OJ 1985, 299) the Enlarged Board held that the motives of the opponent were in principle irrelevant (otherwise, no doubt, the phrase "any person" would have been rendered as "any person interested"), whilst his identity was of primarily procedural importance (similarly in T 635/88, OJ 1993, 608; T 590/93, OJ 1995, 337). Following that case law, the board in T 798/93 (OJ 1997, 363) found that the EPC and its attendant provisions contained no requirements as to the opponent's personal circumstances or motives for acting. Requests for the opposition to be declared inadmissible therefore had to be refused if, as in the case under consideration, they were based on either an objection regarding a particular aspect of the opponent's status, such as his profession (professional representative before the EPO) or his field of technical expertise (different from that of the opposed patent), or on his lack of motives for acting (statement by the opponent saying that his only reason for acting was to complete his training).
The case law on the transfer of opponent status is dealt with separately in Chapter IV.C.2.2. The status of opponent can also be acquired by an assumed infringer who has intervened in pending opposition proceedings (see also Chapter IV.C.3, Intervention).