4.3. Standard of proof

Even though different concepts as to the standard of proof have developed in the case law of the boards, they all have in common that a judgement is to be made on the basis of the application of the principle of free evaluation of evidence (confirmed by G 2/21, point 46 of the Reasons).

The board in T 1138/20, a case that turned on issues of proof, clearly stated (see point 1 of the catchword) that there is only one standard of proof in the proceedings before the EPO: the deciding body, taking into account the circumstances of the case and the relevant evidence before it, must be convinced that the alleged fact has occurred.

Compare G 2/21 (OJ 2023, A85), which, without making as explicit a pronouncement on the standard of proof, nonetheless contains the following passage: "The only decisive factor is whether the judge is personally convinced of the truth of the factual allegation, i.e. how credible the judge classifies a piece of evidence" (for the context see point 31 of the Reasons, and also point 46 of the Reasons cited above).

When a standard is applied, the EPO standard of proof is generally the balance of probabilities. By way of exception, the standard of proof of the balance of probabilities is shifted to a standard of proof beyond reasonable doubt mainly in opposition where only the opponent has access to information (evidence) concerning, for example, an alleged public prior use.

The board in T 1138/20 stated that if, for example, only the opponent had access to the relevant evidence, this fact must be given due consideration in the deciding body's assessment as to what weight and importance are to be attached to such evidence. This was not the same as to say that a different standard of proof should apply.

Of note are some other, earlier decisions containing lengthy observations on the standard of proof and the previous case law on this, namely: T 2451/13 on the meaning of "beyond reasonable doubt" and T 545/08 on the meaning of "balance of probabilities" in the boards' case law; in the latter decision, the board considered the matter in the general context of the law of evidence, concluding that a probability as low as 51% would not suffice.

T 1138/20 contains very detailed reasoning on the standard of proof applicable before the EPO, identifying decisions (T 545/08, T 768/20, T 660/16, T 1634/17) where it was not deemed necessary to explicitly decide on the applicable standard and it was instead emphasised that what mattered was whether the board was convinced. And the board in T 1138/20 considered that making a distinction between the above-mentioned standards was neither necessary nor mandated by case law.

Indeed several decisions have not considered it necessary to decide explicitly which standard of proof applied: see T 2466/13, in which it was found that there was no need to decide on the applicable standard of proof. In the same vein, see T 768/20, T 660/16 citing in particular T 545/08 (points 8 and 11 of the Reasons). In T 464/20, the appellant challenged the standard of proof (balance of probabilities) used at first instance to conclude that prior use had been proven. However the board held that the opposition division had linked its application of the standard to whether it was persuaded that the alleged facts were true. The board was thus not convinced that it had been wrong to apply the standard of the balance of probabilities, especially as the opposition division had been persuaded of the truth of the alleged facts (T 768/20 being concurred with). T 34/08 was another case where the board concluded that it was convinced without referring to a standard of proof. T 1634/17 (point 19 of the Reasons) stated that there was no need to take a stand; what was decisive was that, in view of the evidence before the first-instance department or the board in an individual case, the deciding body was persuaded that a particular oral disclosure had taken place and particular information had been conveyed to the audience or not.

In T 1808/21, on the question of whether appellant 1 had circumvented the law by allegedly lowering the standard of proof required for the public availability of D5 due to its role as a "straw man", the board was convinced that a distinction between the "balance of probabilities" standard and the "beyond any reasonable doubt" standard was not decisive in that case. In line with T 768/20 and T 660/16, the board agreed that the relevant point was instead whether the deciding body was ultimately persuaded in view of all the available facts that the relevant evidence, which had been duly presented by appellant 1 when it filed its opposition, had indeed been made publicly available.