According to the existing case law of the Boards of Appeal, the standard of proof applicable to allegations of public prior use – when the evidence is in the sphere of both parties – is ‘the balance of probability’. However, when the evidence lies entirely in the sphere of the opponent, usually a higher standard of proof, i.e. ‘beyond any reasonable doubt’ (up to the hilt), applies. The two standards would entail a different degree of proof that an alleged fact is correct or has occurred.In T 464/20, the Board stresses that the most relevant question is whether the deciding body is convinced that an alleged fact is correct or has occurred. In the case at hand, the opposition division, in acknowledging the public prior use, applied the ‘balance of probability’ standard. The appellant/patentee objected that the applied standard was not the correct one, because only the respondent/opponent had the control of the evidence.In the decision, in a quite cumbersome sentence, the Board reasoned that even if the Board followed the patentee’s view that practically all the evidence was within the opponent’s control, the Board would still have to be convinced that the choice of the ‘balance of probability’ standard was not correct. The Board was not convinced of the incorrectness of the choice of the standard by the opposition division. In this regard, the Board noted that the opposition division correctly did not base its decision exclusively on the question whether the alleged facts were probable; rather, they were convinced of their correctness. Indeed, the opposition division was convinced both that the delivery of the product at issue was not exclusively in the hands of the opponent and that it had actually occurred.The Board further relied on two previous Boards of Appeal decisions to support its opinion.They referred to T 548/08, in particular reasons 4 to 11. T 548/08 deals with the type of standard of proof (‘beyond any reasonable doubt’ versus ‘the balance of probability’) to be applied to assess whether an internet disclosure forms part of the prior art. The Board commented that it was aware of the different views expressed in the case law on the standard to be applied.However, the Board stated that the European Patent Convention’s (EPC) overarching principle of free evaluation of evidence (referring to decision G 1/12, OJ EPO 2014, A114, point 31) would reconcile the two different points of view. G 1/12’s reason 31 states that the proceedings before the European Patent Office (EPO) are conducted in accordance with the principle of free evaluation of evidence and that this principle would be contradicted by laying down firm rules of evidence defining the extent to which certain types of evidence were, or were not, convincing.Accordingly, in reason 11, the Board stressed that the facts on which any finding of public availability is to be based must be established with a sufficient degree of certainty in order to convince the competent organ of the EPO that the facts have indeed occurred. This holds true even if the determination is made on the basis of probabilities and not on the basis of absolute certainty (‘beyond any reasonable doubt’).T 768/20, in particular reason 2.1.2, is the second decision mentioned. This decision addresses the point whether, in assessing Art. 123(2) EPC, the implicit disclosure of a certain feature had to be proven beyond any reasonable doubt. The Board found that the applicable standard is ‘beyond any reasonable doubt’. However, the Board noted in reason 2.1.2:“Incidentally, the Board wishes to point out that the practical relevance of the distinction between the “balance of probabilities” standard and the “beyond reasonable doubt” standard is often overestimated. Both standards are only fulfilled if the deciding body is persuaded that the alleged fact is true, which is not a matter of “just tipping the balance slightly” (see decision T 545/08, point 8 of the reasons). This is also confirmed by the passage in case law, section III.G.4.3.1, according to which “the balance of probabilities standard [is] met if, after evaluating the evidence, a board [is] persuaded one way or the other” (underlining by this board).”The Board of T 464/20 then considered the available evidence and concurred with the opposition division that the public prior use was ‘sufficiently’ proved.Decisions T 464/20, T 545/08 and T 768/20 deal with the standard of proof in different contexts (prior use, internet disclosure, Art. 123(2) EPC). In each of these cases, the competent Board, without denying the distinction between the two standards, appears to emphasise that what matters is that the deciding body is convinced that the alleged fact is correct or has occurred. Therefore, in the case of the standard of probability, it is not sufficient to show that an alleged fact has merely “probably” occurred.