5.1.1 General

In the absence of relevant EPC provisions, the principles concerning the allocation of the burden of proof have been developed through the case law of the boards of appeal. Each party bears the burden of proof for the facts it alleges.

According to the established case law of the boards of appeal, each party to the proceedings bears the burden to prove the facts that it asserts. If a decisive fact is not proven, the decision taken will be to the detriment of the party that fails to provide the necessary proof (see decision T 270/90, OJ 1993, 725, point 2.1 of the Reasons; T 355/97, point 2.5 of the Reasons; T 527/08, point 3.4.1 of the Reasons; T 1469/08 "Public prior use (no): public availability not sufficiently proven").

In T 219/83 the board had held that it is not sufficient in opposition proceedings for the opponent to impugn a granted patent with an assertion which cannot be substantiated. And if the EPO is unable to establish the facts of its own motion (Art. 114(1) EPC), the proprietor is given the benefit of the doubt (T 219/83, OJ 1986, 211, 328; see also T 293/87 and T 459/87, T 200/94 (Art. 56 EPC – experimental evidence – conclusion: problem credibly solved across entire scope), T 762/04 point 4.8.1 of the Reasons).

Example decisions summarising the consequences of making assertions without any evidence to support them (extracts out of context in brackets): T 882/17 (the allegation merely speculative and not supported by any evidence); T 346/03 with regard to a question of admissibility ; T 707/21 (the appellant's unsupported allegation that for the skilled person also the distinguishing features found to be generic and manifestly speculative); T 1540/21 (only one specific allegation based on verifiable evidence.); T 1837/13 (the appellant nevertheless asserts, without providing any proof ... the board regards this assertion as purely speculative and cannot take it into account in its decision ... and if a decisive fact is not proven...); T 2233/08 (the absence of any data supporting them, the allegations provided by the appellant – who had the burden of proof for them – were found to be entirely speculative and had to therefore be disregarded); T 592/08 (absent any evidence confirming an effect is achieved ... the assertion that such effect is achieved over the whole claimed scope remains speculative and cannot be taken into account in the assessment of inventive step.); T 51/97 (in the absence of any corroborating evidence the respondent's allegation was speculative and did not convince the board.) ; T 523/18 (the argument that one or the other distinguishing feature did not contribute to the effect demonstrated amounted to a mere allegation, unsupported by evidence.); T 40/17 (the assumed intention of the appellant to cause unnecessary costs was a mere allegation ; it could not justify the requested apportionment of costs); T 61/20 (the reference to the skilled person's common general knowledge was a mere allegation without any evidence); T 2038/19 (the absence of evidence showing the knowledge of the skilled person, in particular in relation to the production of water-absorbent resin particles, constituted a mere allegation devoid of any concrete support and was not persuasive); T 1310/22 (the argument at issue constituted a mere allegation devoid of any concrete support and was for this reason not persuasive), see also T 1469/08 ; T 2916/19.

– Burden of presentation and burden to prove a negative fact

T 2037/18 concerned whether an opposition had met the requirements for "adequate substantiation" and thus been admissible and, in particular, whether the opponent, which had alleged a prior use, should have substantiated an asserted lack of a non-disclosure clause. Addressing in detail the burden of proof and the burden of presentation, the board held that in most legal systems and in proceedings before the EPO (beyond the area open to examination by the EPO of its own motion), the burden of presentation and the burden of proof were allocated such that each party had to present and prove the facts that were favourable to them, i.e. the facts that supported their own assertions (T 219/83, T 270/90). The principle of "negativa non sunt probanda", also recognised in the boards' case law (see R 15/11, R 4/17), was a clear expression of this allocation of the burden of proof. In other words, a party to the proceedings was not required to prove a negative fact. As a general rule, the burden of presentation followed the burden of proof. Decision applied in T 1714/15 (Art. 83 EPC – burden to prove that a measurement apparatus no longer existed), T 503/20 (patent proprietor bears the burden of proving and producing evidence of an implicit confidentiality agreement) and T 1529/20 (proof that a notification was not received).

Another decision related to proving a negative fact with reference to T 1798/14 (obligation to maintain confidentiality): T 34/18 (prior use – extent of the requirement for the opponent to provide proof that there was no obligation to maintain confidentiality; see in particular point 4.2.3 of the Reasons).

In T 998/04 the board emphasised as an obiter dictum that the burden of proof for alleged lack of patentability lay with the opponent and could not be dispensed with by requesting the board to carry out its own investigations, in particular, by summoning four named witnesses, by commissioning an independent expert to carry out experimental tests and by allowing individuals from the appellant company to attend any tests and to question witnesses or experts. Moreover, granting these requests would not be consistent with the character of the post-grant opposition proceedings under the EPC which were in principle to be considered as contentious proceedings between parties normally representing opposite interests, who should be given equally fair treatment (see G 9/91, OJ 1993, 408, point 2 of the Reasons).

– Taking doubt into account

If a material fact is not or cannot be proven, a decision is taken as to who bears the relevant burden of proof. If the real position cannot be established, this is to the detriment of the party who bears the burden of proof for this fact, among other things because the other party is given the benefit of the doubt. In principle, each party bears the burden of proof for the facts it alleges (T 63/06, points 3.1 and 3.2 of the Reasons).

In T 1076/21 the board, which also made reference to the passage cited above from T 63/06, stated that since the parties in the case in hand made contradictory but unsubstantiated assertions concerning facts, the patent proprietor was given the benefit of the doubt (T 72/04, point 3 of the Reasons).

In case of uncertainty about a prior-art disclosure, the patentee should be given the benefit of the doubt (T 1003/96; see also T 230/92, T 345/86, T 601/91 and T 968/91). On the issue of taking doubt into account in the examination of Art. 123(3) EPC, see T 2285/09.

See also T 832/22 which addresses the meaning of a remaining doubt in relation to the "beyond reasonable doubt" standard.

– Irrelevance of access to evidence for apportioning the burden of proof

The patentee cannot relieve itself of the burden of providing counter-evidence for facts it alleges by simply stating that all the evidence was within the power of its opponent (with reference to T 472/92, OJ 1998, 161;), without providing proof for the contention that it is not within its power to obtain counter-evidence (T 254/98). As far as apportioning the burden of proof is concerned, it is irrelevant whether or not the patentee can access the requisite evidence more easily than the opponent (T 1162/07; see also T 1710/12).