9.1. General principles

According to established case law of the boards of appeal, a successful objection of insufficient disclosure presupposes that there are serious doubts, substantiated by verifiable facts. In inter partes proceedings, the burden of proof initially lies with the opponent, who must establish, on the balance of probabilities, that a skilled person reading the patent, using common general knowledge, would be unable to carry out the invention. This initial burden on the opponent may shift to the patent proprietor once the opponent has successfully discharged its burden of proof.

Indeed, a successful objection of a lack of sufficiency of disclosure presupposes that there are serious doubts, substantiated by verifiable facts (see e.g. decision T 19/90, OJ 1990, 476 and decision T 890/02, OJ 2005, 497). In order to establish insufficiency of disclosure in inter partes proceedings, the burden of proof is upon an opponent to establish, on the balance of probabilities, that a skilled person reading the patent, using common general knowledge, would be unable to carry out the invention (see decision T 182/89, OJ 1991, 391). Citing T 182/89 on this point, the board in T 406/91 stated that a mere statement that one of several examples in a patent had been repeated once "exactly as described" without obtaining exactly the results claimed in the patent was in principle inadequate to release the opponent from that burden (see T 406/91, as well as T 418/91, T 548/91, T 588/93, T 465/97, T 998/97, T 499/00, T 751/00 and T 967/09).

The board in T 642/22 stated that T 19/90 (successful objection based on serious doubts substantiated by verifiable facts) did not mean that the opponent necessarily had to provide evidence such as experimental data showing that the claimed furan levels could not be achieved. Instead, the existence of verifiable facts which may give rise to doubts as to the sufficiency of the disclosure could be inferred from the patent itself or from common general knowledge (T 2038/19, T 1187/20).

On how to determine who bears the burden of proof at the appeal stage, see T 1138/20 for general considerations, and more specifically T 1076/21 on objections under Art. 83 EPC.

In view of all the issues addressed in T 1076/21 and its confirmation and clarification of key concepts and how they interrelate, specifically with regard to Art. 83 and 100(b) EPC and the law of evidence, this recent decision deserves to be reported in detail here.

Confirmation and clarification in T 1076/21 of the principles of the law of evidence in relation to Art. 83 EPC:

In T 1076/21 the respondent (opponent), referring to T 585/92, argued that, because the opposition division had revoked the patent, the appellant (patent proprietor) bore the burden of proving that the patent was sufficiently disclosed. The appellant disputed that the respondent had successfully discharged its initial burden of proof. The board concluded that the burden of proof regarding the facts, arguments and evidence on the substance (which initially lay with the opponent) did not shift to the proprietor just because the patent had been revoked due to an alleged insufficient disclosure. The board recalled that only if there were serious doubts, substantiated by verifiable facts, could an application (or a patent) be objected to for insufficient disclosure (T 19/90). After the grant of the patent, there was a legal presumption that the patent met the requirements of the EPC. This presumption could be rebutted. The weight of the submissions required to rebut the presumption depended on its strength. A strong presumption required more substantial submissions than a weak one. In the context of the ground of opposition of sufficiency of disclosure, the strength depended on the way the invention was disclosed in the patent (T 63/06, T 55/18). The initial burden on the opponent to provide facts, arguments and evidence for an assertion of an insufficient disclosure could shift to the patent proprietor once the opponent had successfully discharged its burden of proof by submitting sufficient facts, arguments and evidence to rebut the presumption of sufficiency (T 338/10, T 2218/16). However, this shift could only be caused by sufficient submissions on the substance; formal reasons alone, like the mere existence of the opposition division's decision to revoke the patent, did not lead to a shift of the burden of proof on the substance. If the reasoning in the impugned decision as such was found to be wrong, there could not be any shift of the "burden of proof on the substance" (T 499/00, T 1608/13).

Linked to the burden of proof was the "burden to substantiate a case". Thus, the opponent first had to provide facts and argue why these facts supported its assertion (T 182/89). This burden of substantiating facts and arguments was then followed by the burden of proving these facts, which was normally done by submitting evidence. Only in the exceptional case of a weak presumption of validity due to a lack of information in the patent could the submission of plausible arguments alone be sufficient (T 63/06, T 1558/11). The two aspects were often referred to together as the burden of proof.

This might have led to the misconception that any decision finding insufficiency would lead to the burden of proof being shifted to the patent proprietor. However, when distinguishing the "burden to substantiate a case" from the "burden of proof on the substance", the board found that it could be clearly deduced from the case law that after a decision by the opposition division allowing an objection of insufficiency, it was down to the patent proprietor to substantiate on appeal why that decision was wrong. However, the burden of proof on the substance (and in consequence the benefit of the doubt) only shifted if the opposition division's assessment that the presented facts, arguments and evidence had been sufficient to discharge the opponent's burden of proof turned out to be correct. The appellant bore the burden of substantiating the appeal. The board nevertheless noted that an appeal case did not necessarily need to be substantiated by submitting facts and evidence that countered the arguments and evidence presented by the opponent. It could also be substantiated by submitting why the opposition division's reasoning on insufficiency was flawed and why the burden of proof on the substance still lay with the opponent.

The patent proprietor in T 1076/21 had substantiated its appeal, whereas the respondent had not submitted evidence that the guidance in the patent was insufficient or shown that the allegedly unusual parameter was indeed unusual, which meant it had not discharged its burden of proof on the substance. The opposition division had not been unable to base its decision on verifiable facts as required. There had been no shift of the burden of proof to the patent proprietor. As regards another aspect, the board concluded that since the parties had made contradictory but unsubstantiated assertions concerning facts, the patent proprietor ought to be given the benefit of the doubt (T 72/04).

Application of T 1076/21 in case law:

In T 127/22 the board, with reference to T 1076/21, said that the burden of proof did not shift to the proprietor solely by the fact that the patent had been revoked in opposition proceedings due to the alleged insufficient disclosure. In the present case, however, there were further reasons that justified a shift in the burden of proof to the proprietor. When the patent did not give any information as to how a feature of the invention could be put into practice, only a weak presumption existed that the invention was sufficiently disclosed. In such a case, the opponent could discharge their burden by plausibly arguing that common general knowledge would not enable the skilled person to put this feature into practice. In the present case there was only a weak presumption in favor of the proprietor. The board came to the conclusion that in the absence of any indication or any clear guidance on the testing conditions, it was not possible to reliably and accurately determine the relative gas flows in different zones of the catalyst article.

In case T 1708/22 (allegedly ill-defined density parameter – but different methods known - accessible commercial product of which composition could be determined – lack of evidence provided by opponent), with reference to T 1076/21, the board decided that the burden of proof had not shifted to the appellant (patent proprietor) just because the opposition division had arrived at the conclusion that the patent did not meet the requirements of Art 83 EPC.

The following sections deal with some particular aspects related to evidence. On the special case of parameters, see also chapter II.C.5.5.3. On second medical uses, see chapter II.C.6.8. "Postpublished documents" and II.C.7.2. above and e.g. the recent decisions T 1394/21, T 2790/17, T 1210/20, and T 1779/21, with reference to G 2/21 (OJ 2023, A85, points 74 and 77 of the Reasons).