According to the established jurisprudence of the boards of appeal the assessment of inventive step is to be made at the effective date of the patent on the basis of the information in the patent together with the common general knowledge then available to the skilled person (T 609/02, T 1329/04, T 1545/08). Moreover, there can only be an invention if the application makes it at least plausible that its teaching indeed solves the problem it purports to solve. The boards have regularly considered in the context of the evaluation of inventive step whether or not "the problem is solved" (T 939/92, OJ 1996, 309) and have in cases where they were not satisfied that this was so, i.e. that what was claimed was de facto a solution to the problem, denied an inventive step (T 210/02, T 1329/04) or required a reformulation of the problem (T 939/92, T 87/08). According to decision T 1329/04, the verification of whether or not the claimed solution actually solves the problem, i.e. whether the claimed subject-matter actually provides the desired effect, must be based on the data in the application. Post-published evidence to support that the claimed subject-matter solves the problem to be solved is taken into account if it is already credible from the disclosure in the patent that the problem is indeed solved. In other words, supplementary post-published evidence may not serve as the sole basis to establish that the problem is solved (T 1329/04, T 415/11, T 1791/11, T 488/16). Common general knowledge at the priority date may be used to interpret the teaching in an application or a patent. Post-published evidence can only be used to back up the teaching derivable from the application (T 716/08, T 578/06).

In T 716/08 the board stated that as to the quality of the evidence, "absolute proof" of the achievement of an effect is not required for the effect to be "plausible".

In T 578/06 the board stated that the EPC requires no experimental proof for patentability and considered that the disclosure of experimental data or results in the application as filed and/or post-published evidence is not always required to establish that the claimed subject-matter solves the objective technical problem. This is in particular true in the absence of any formulated substantiated doubt. The board re-emphasised in this context however that this case law considers the establishment of plausibility only relevant when examining inventive step if the case in hand allows the substantiation of doubts about the suitability of the claimed invention to solve the technical problem addressed and when it is thus far from straightforward that the claimed invention solves the formulated problem. This is all the more clear from decisions where an inventive step was in fact denied because the formulated problem was not considered to have been solved. By way of example the board referred to T 893/02 and T 1329/04.

In T 433/05 the board referred to decisions T 1329/04 and T 1336/04 when deciding whether the technical problem had indeed been solved by the subject matter of claim 1 at the relevant date (see also T 1306/04, T 710/05, T 1396/06).

In T 1329/04 it was stated that the definition of an invention as being a contribution to the art, i.e. as solving a technical problem and not merely putting one forward, required that it was at least made plausible by the disclosure in the application that its teaching indeed solved the problem it purported to solve. Therefore, even if supplementary post-published evidence might, where appropriate, also be taken into consideration, it could not serve as the sole basis for establishing that the application did indeed solve the problem it purported to solve. In the case before it, the board decided that the post-published evidence could not be regarded as supportive of evidence which would have been given in the application as filed since there was none. Since the post-published evidence was considered to be the first disclosure going beyond speculation, it was not taken into consideration.

The same Board 3.3.08, confronted with a different technical situation, namely one where the quality of evidence provided in the patent in suit was such that the claimed invention was considered to be a bona fide solution to the problem to be solved, accepted the solution of the problem by also taking into consideration the disclosure in a post-published document (T 1336/04).

Considering decisions T 1329/04 and T 1336/04, the board was convinced in T 433/05 that the circumstances of the case were appropriate to take into account a supplementary post-published document when establishing whether the application indeed solved the problem it purported to solve. In the light of the disclosure in the patent in suit, which was supported by a post published document, the board was satisfied that the problem was solved by the subject-matter of the claims.

In T 778/08 the post-published documents were taken into account because they simply provided a confirmation that the general concept of the method of the invention was sound. In reaching this conclusion, the board did not deviate from T 1329/04. In the case in hand, the experimental data provided in the application as filed rendered the alleged effect and its solution plausible, the post-published documents could not be regarded as the first disclosure going beyond speculation, but rather additionally confirmed that the general concept of the claimed invention worked.

In T 2371/13, however, the board held that the fact that an effect had to be regarded as implausible because it was not backed up in the application was not a good enough reason to disregard comparative tests filed later with a view to proving it. To do so for that reason would run counter to the problem and solution approach: it required that a technical problem be defined in light of the closest prior art, which was not necessarily that cited in the application. It was common, the board observed, to try to demonstrate inventive step on the basis of a technical effect not explicitly mentioned in the application as filed. The objection that the invention had yet to be achieved when the application was filed was anyway more a matter for consideration under Art. 83 EPC.