d) Substantiation to be distinguished from strength of the opponent's case 

In T 934/99 the board stated that R. 55(c) EPC 1973 (R. 76(2)(c) EPC) did not imply the requirement of a logical line of reasoning in the sense that the arguments brought forward in the notice of opposition had to be cogent or convincing. Rather, the criterion was whether the arguments presented were relevant and, where necessary as the result of a reasonable interpretative effort, specific enough to allow a person skilled in the art to form a reasoned opinion of whether the line of reasoning on which the opponent apparently relies was (logically) correct ("convincing") or not (i.e. wrong).

The sufficiency of the notice of opposition has to be distinguished from the strength of the opponent's case. On the one hand, an unconvincing ground for opposition might have been clearly presented and argued. Conversely, a deficient submission may be rejected as inadmissible even though, if properly drafted, it would have succeeded (T 222/85, OJ 1988, 128; T 621/91, T 3/95, T 1069/96, T 1856/11).

In the same vein, in T 65/00 the board held that it was of no importance for admissibility whether the relevance of the arguments brought forward, or their correctness, was sufficient to revoke the patent. In the case at issue it was therefore irrelevant whether the arguments brought forward by the opponent referred to Art. 84 or Art. 83 EPC 1973. For admissibility it was sufficient that the arguments were such that an arguable case was established. See also T 623/18.

Similarly, the board in T 1194/07 referred to the established case law, according to which the indication of facts, evidence and arguments need not be conclusive or correct. That is an issue of merit. However, the board also emphasised that the merits of a case can only be assessed in a meaningful manner if the case has been stated fully, by an adequate indication of the relevant facts, evidence and arguments. Key elements linking the cited prior art to the claim or relating to their validity as evidence, as well as crucial arguments informing the reader why the skilled person might have considered combining the features of such prior art with those of the accompanying evidence, should not be missing in the notice's chain of logic leading from the prior art to the invention.