d) Adequate reasoning in an appeal filed by the opponent 

It is established case law of the boards of appeal that appeals by opponents – as opposed to appeals by proprietors, which would need to address all objections withstanding the maintenance of the patent – are sufficiently reasoned where they make a substantiated case for the decision under appeal being wrong on one of the objections or grounds for opposition. That was because, if the decision were indeed wrong on that point, the appeal had to be allowed for this reason alone (T 767/14, see also T 950/99, T 846/01, T 87/17, T 456/17). For such an appeal, therefore, it is also immaterial if the case is lacking as regards other aspects dealt with in the contested decision. If an opponent's statement of grounds of appeal is insufficiently reasoned in relation to specific parts only, this does not mean the appeal is inadmissible, because admissibility can only be assessed in light of the appeal as a whole (T 2270/17).

In T 950/99, the statement setting out the grounds of appeal included the legal and factual reasons why the decision under appeal should be set aside with respect to at least one ground, namely lack of inventive step. Therefore, even if it did not contain a full reasoning with respect to each and every ground, it nevertheless met the minimum requirement of Art. 108 EPC. In T 808/01, the board held that, where the statement of grounds contained several lines of argument and reasons sufficient to render the appeal admissible had been given in support of at least one of them, the appeal was admissible and it did not matter that no such reasoning had been given in support of one of others.

In T 846/01, the board held that, for an appeal to be admissible, at least one of the grounds in the written statement of grounds of appeal must relate to a point which could at least arguably have been decided in the appellant's favour by the instance appealed from but which point had not been so decided, and such favourable decision on this point would have produced a different outcome. Following T 846/01, the board in T 1178/04 confirmed that an appeal does not lie against part of a decision of a first instance tribunal if the result would have been the same even if the point had been decided in the appellant's favour.

In T 1187/04, where the appellant had dealt only with the novelty objections and not addressed inventive step, the appeal was held inadmissible.

In T 257/03, since all the board could gather from the statement of grounds was that the appellant sought the reopening of the entire opposition proceedings, but not why it considered that the opposition division's decision should be amended, it dismissed the appeal as inadmissible.

In T 1649/10 the board held that the mere indication by appellant II (patentee) that the subject-matter of granted claim 1 was inventive, starting from document D4 as the closest prior art, whereas the impugned decision based its analysis on a combination of D10 as the closest prior art and document D4, did not fulfil the requirements of R. 99(2) EPC. The board was not in a position to recognise in the reasoning put forward by appellant II, why the reasoning of the opposition division, which relied on document D10 as closest prior art, had to be rejected. The appeal filed by appellant II was, hence, rejected as inadmissible. Its role in the appeal proceedings was then that of a party as of right under Art. 107 EPC.