The extent to which amendments may be admissible in opposition proceedings was discussed in T 1149/97 (OJ 2000, 259). Once a decision to grant has been issued, the European examination procedure is closed and its results become binding on the applicant and the EPO in that no further amendments may be made. However, if an opposition is filed, the patent in suit may be amended. Such amendments are not left to the general discretion of the patent proprietor, since opposition proceedings are not a continuation of the examination proceedings (G 1/84, OJ 1985, 299). However, the patent proprietor may, pursuant to R. 80 EPC (R. 57a EPC 1973) – without prejudice to R. 138 EPC (cf. R. 87 EPC 1973) – react to the opponent's objections by amending the description, claims and drawings, provided that the amendments are occasioned by the grounds for opposition specified in Art. 100 EPC, even if the respective ground has not been invoked by the opponent. In addition, amendments occasioned by national rights of earlier date are admissible pursuant to R. 138 EPC (see also in this chapter IV.C.5.1.2).

According to the board, those regulations could be seen to reflect the formal aspects of a procedural cut-off effect associated with the grant of a patent in the opposition phase. Compliance with the restrictions imposed by R. 57a and 87 EPC 1973 (R. 80 and 138 EPC) was thus a prerequisite for any further considerations as to possible substantive cut-off effects for amendments after grant during opposition proceedings which, in the board's view, could only be based on Art. 123(3) EPC (see also chapter II.E.2.3.2).

In T 750/11 the board observed that amendments under R. 80 EPC were formally admissible so long as they could be regarded as a serious attempt to overcome a ground for opposition. So an amendment further limiting the subject-matter of an independent claim complied with R. 80 EPC in formal terms. Whether it actually overcame any ground for opposition was a separate matter to be settled as part of the ensuing substantive examination.

According to T 323/05, which concerned a request to adapt the description, R. 57a EPC 1973 (R. 80 EPC) establishes a limit to the amendments which can be made to the patent in suit. Art. 84 EPC 1973 and R. 57a EPC 1973 are the two provisions which have to guide the patent proprietor when he is invited by the opposition division to adapt the description. In other words, the amendments have to be appropriate and necessary, and nothing more.

In T 993/07 the board recalled that R. 80 EPC is lex specialis for amendments during opposition proceedings, analogous to R. 137 EPC for amendments during examination proceedings. The board interpreted the rule to mean that in opposition proceedings the proprietor's right to amend the patent, e.g. the claims as granted, is limited to making amendments in order to overcome an objection based on a ground for opposition as specified in Art. 100 EPC, thereby possibly avoiding revocation of the patent. In line with this interpretation, the board stated that opposition proceedings were not to be understood as an opportunity for the proprietor to fix any, from his perspective, shortcomings in the patent, such as an insufficient number of independent and/or dependent claims in order to define all commercially valuable embodiments. The fact that the addition of one or more independent and/or dependent claims may improve the fall-back positions in any future revocation proceedings before a national court was clearly not the scope and purpose of either R. 80 EPC or the opposition procedure. The board also observed that a limitation procedure pursuant to Art. 105a EPC is not subject to the same requirement as set out in R. 80 EPC.

In T 359/13 the board stated that R. 80 EPC did not place any restriction on the form of amendments a patent proprietor may (seek to) make to address objections raised (here: reformulating the product claim as a use claim). On the contrary, a patent applicant or proprietor was free to draft proposed amendments to the specification in any manner considered appropriate. Even in the situation considered in G 1/99 where the requirements of the principle of no reformatio in peius imposed restrictions on the manner in which the claims may be amended, an opponent as appellant had no right to prescribe the form of the amendments which the patent proprietor as respondent may make (see T 23/04).

In T 2290/12, the appellant had used parts of a claim found by the opposition division to lack inventive step in a series of new independent claims which also included features taken from the description. The board considered such an approach legitimate, provided it did not amount to an abuse of procedure and the number of independent claims was not unreasonably high. Since lack of inventive of step was a ground for opposition, R. 80 EPC had in any event not been infringed.

The opposition division's decision to admit into the proceedings an auxiliary request (main request in the appeal proceedings) filed during the oral proceedings was challenged before the board in T 491/09. In its decision the board concluded that the opposition division had properly exercised its discretion according to R. 116(1) and (2) EPC by taking into account the following criteria:

a) prima facie allowability: contrary to the opponent's/appellant's argument that the opposition division should have examined the prima facie clarity of the claims, it was evident from the minutes of the oral proceedings that no such objections had been raised. Also, the board could not share the appellant's view that the opposition division should ex officio have examined the entire claim for clarity, following T 1459/05 and T 656/07 (on this issue, see now G 3/14, OJ 2015, A102, in this chapter IV.C.5.2.2). Apart from the fact that T 656/07 was issued after the oral proceedings at the opposition stage and that, in general, the opposition division could hardly be expected to receive knowledge of any single decision immediately after its deliverance, the board could not find any fault with the opposition division not following a decision which expressly stated that it concerned a very particular case and warranted a departure from otherwise consistent case law.

b) procedural expediency/abuse of procedure: the board recognised that the respondent (patent owner) needed quite some prompting to finally come up with its late-filed request which addressed the point under discussion during the oral proceedings before the opposition division, but could not see an abuse of procedure therein, nor an unwarranted advantage for the respondent.

c) reasonable expectation that the opponents familiarise themselves with the proposed amendments in the time available: the minutes revealed that the oral proceedings had been conducted properly and towards the resolving of the outstanding issues, giving the opponent ample opportunity to familiarise itself with the amended subject-matter.

For another decision approving these criteria, see e.g. T 500/15, which also elaborates on the criterion of complexity of amendments as well as the need to give individualised reasons, taking into account the concrete request.

In T 754/16 the board emphasised that for the opposition division to have discretion not to admit new requests, these had to be late filed in the first place (see in this chapter IV.C.5.1.3 below).

Since the EPC does not provide for surrender of the patent in opposition proceedings, so that – even if they issue an express statement to that effect – patent proprietors cannot surrender their patent either wholly or in part during such proceedings, they can merely request that the patent be amended. In requesting that the patent be maintained in a limited form, a patent proprietor is merely attempting to delimit it to meet objections raised by the EPO or the opponents and does not, by virtue of such limitation, irrevocably surrender subject-matter not covered by the request as limited. In principle, the patent proprietor is free to withdraw such a request at any time during opposition proceedings or to amend it subsequently and, in particular, to resume a defence of the patent as granted, unless this would constitute an abuse of procedural law or the proprietor is prevented from doing so by the prohibition of reformatio in peius (see T 123/85, OJ 1989, 336; T 296/87, OJ 1990, 195; T 155/88; T 225/88; T 217/90; T 715/92; T 752/93 of 16 July 1996 date: 1996-07-16; T 1037/96; T 445/97; T 473/99; T 880/01; T 794/02; T 934/02; T 1213/05; T 1394/05; T 1150/11).

According to the case law in T 123/85 (OJ 1989, 336), there is nothing to stop patent proprietors who have defended only a limited version of their patent in opposition proceedings from seeking to reinstate the patent as granted in any subsequent appeal proceedings. However, this is subject to the conditions laid down in G 9/92 date: 1994-07-14 and G 4/93 (OJ 1994, 875; accordingly, the position taken in T 369/91 date: 1992-05-15, OJ 1993, 561, is obsolete). The board in T 1150/11 reiterated the settled case law that previous limitations of the claims cannot be treated as an express abandonment of parts of the patent but are to be regarded merely as attempts to come up with a wording delimiting the patent such as to overcome objections. It could see no reason to depart from that case law. See also T 385/15.

In G 1/10 (OJ 2013, 194), the Enlarged Board of Appeal held that R. 140 EPC is not available for correcting patents, including during opposition or limitation proceedings. However, it is always open to a patent proprietor to seek to amend his patent during opposition or limitation proceedings and such an amendment could remove a perceived error. Such an amendment would have to satisfy all the legal requirements for amendments including those of Art. 123 EPC (see also full summary of G 1/10 in chapter III.L.2.1.).