5.2. Shifting the burden of proof
5.2.1 General
Once a party has submitted conclusive proof of its allegations, it has complied with the requirement of the burden of proof. The evidence need not prove the facts with absolute certainty in order to be deemed conclusive; it suffices that it proves that they are highly probable. If a party has discharged its burden of proof, the counterparty seeking to refute the conclusively established facts by way of counter-arguments bears the burden of proving the alleged facts (T 1162/07 summarised in T 2037/18; see also T 270/90, OJ 1993, 725). In T 109/91 the board held that the burden of proof might shift constantly as a function of the weight of the evidence, i.e. if a party provided enough evidence to demonstrate a fact to the conviction of the board, the mere allegation of the contrary by the other party is not convincing (confirmed e.g. in T 525/90, T 239/92 and T 838/92).
In ex parte proceedings, when the applicant challenges prima facie evidence concerning a fact, i.e. the nominal publication date of a document, and submits evidence to displace such prima facie evidence, the burden of proof shifts to the examining division to establish that the document was "made available to the public" within the meaning of Art. 54(2) EPC on that date (see T 929/94 with reference to T 750/94, OJ 1998, 32). According to T 128/87 date: 1988-06-03 (OJ 1989, 406), a party presenting a cheque to the EPO bore the burden of proof for its receipt by the EPO. However, if the party furnished sufficient proof that a certain document had been filed, such evidence shifted to the EPO the burden of providing a greater weight of evidence to the contrary (T 770/91 and J 20/85, OJ 1987, 102). The more recent case T 538/09 addressed this issue of burden of proof and standard of proof in its analysis of T 750/94 and T 151/99.
In ex parte case T 545/08 the board said that it is a general principle that, when the examining division raises objections, the burden of proof lies initially with it. This means that objections must be reasoned and substantiated, and must show that, on the balance of probabilities, the objection is well-founded (see EPC Guidelines G‑IV, 7.5.3 – April 2025 version). With respect to the publication date of a cited document, at least prima facie evidence is required. Prima facie evidence means evidence which is sufficient, on its own, to establish a fact or to raise a presumption of the truth of a fact unless controverted (see T 750/94, point 6 of the Reasons; T 526/12, point 1.4 of the Reasons; T 1066/13, "directory listing" – no prima facie evidence). Thus, not every indication or hint qualifies as prima facie evidence. If the objection is properly raised, it is then up to the applicant to prove otherwise or at least to submit evidence to displace the prima facie evidence. If the applicant successfully challenges prima facie evidence concerning a fact, e.g. the nominal publication date of a document, the burden of proof shifts back to the examining division to establish that the document was made available to the public (see e.g. T 929/94, point 2.1 of the Reasons). As to the case in hand in T 545/08, the board found, among other things that, in the absence of prima facie evidence of the public availability of document D1, the examining division had not been entitled to consider it as prior art in its first substantive communication without providing further explanations and evidence as to its public availability before the priority date (see also T 1961/13). Thus, the objection was not properly raised. It could not generate an obligation on the applicant's side to submit evidence against the assumed publication date.
In inter partes proceedings with reference to T 585/92 cited by the opponent (respondent) in T 1076/21 in relation to an objection of insufficient disclosure, the board addressed the issue of the burden of proof on appeal in detail. The board concluded in essence that the burden of proof did not automatically shift on appeal because the opposition division had revoked the patent; it only shifted once the opponent had discharged its burden of proof (for details, see the longer summary of T 1076/21 in chapter II.C.9).
The board in T 734/18 noted that none of the cases cited by the appellant-patentee (T 2451/13, T 202/13 or T 2338/13) supported the view that the burden of proof should be shifted due to a common sphere of interest between the parties. These decisions rather turn on a legal relationship between parties such as that of a subsidiary, affiliated company.
- T 0449/23
In T 449/23, regarding claim 1 of auxiliary request 1 (claims 1 and 2 being identical to claims 2 and 3 of the main request, after claim 1 of the main request was deleted following a finding of lack of inventive step over D5), the board came to the conclusion that the alleged effects of the distinguishing features were not credible, contrary to the arguments of the patent proprietor. Hence, any alleged effects arising from this comparison could not be taken into account in the formulation of the objective technical problem. The patent proprietor also argued that the burden of proof lay with the opponent to demonstrate that the alleged technical effects were not present. The board disagreed, stating:
(a) that the legal burden of proof was the duty of a party to persuade the deciding body of allegations of facts on which the party’s case rested. In principle, a party must prove alleged facts (assertions) from which it infers a legal consequence, i.e. which establish the basis for the party's legal claims. Thus, the allocation of the burden of proof depends on a party’s substantive case.
(b) that to discharge its legal duty of persuasion, a party must prove the alleged facts by appropriate evidence to the required standard of proof. The party with whom the legal burden of proof lies therefore bears the risk that the alleged facts remain unproven, and thus that the deciding body will decide against that party and reject its legal claims. Thus, the legal burden of proof requires the production of appropriate evidence to persuade the deciding body to the required standard.
(c) that in principle the legal burden of proof does not shift. References in the case law to a shift of burden of proof relate to the so-called evidentiary/evidential burden of proof (see for this distinction T 741/91), the notion of which relates to the state of the evidence produced in the course of proceedings. Once the party bearing the legal burden of proof has adduced sufficient evidence to support its allegations of facts to the required standard of proof, the onus is on the adverse party to rebut the asserted facts with appropriate evidence. Otherwise, the adverse party risks that the deciding body is persuaded of the existence of the facts and allows the claims. Thus, if the party having the legal burden of proof has made a "strong case" by filing convincing evidence, the onus of producing counter-evidence shifts to the adverse party. However, this does not mean that the legal burden of proof is on the adverse party to prove the non-existence or the contrary of asserted factual allegations. It is sufficient that the adverse party raises substantiated doubts that prevent the deciding body from being persuaded of the existence of the alleged facts.
(d) that in opposition and opposition-appeal proceedings, each of the parties carries the legal burden of proof for the asserted allegations of facts on which their respective substantive case rests. As regards an alleged lack of inventive step, the burden is on the opponent to adduce appropriate prior art which – when following the established substantive test, i.e. the problem-solution approach – persuades the opposition division or the board of the obviousness of the solution provided by the subject-matter claimed. On the other hand, if the patent proprietor asserts that, in comparison to the prior art, there is an advantage or effect giving rise to a more ambitious formulation of the objective technical problem than that presented by the opponent and hence to an inventive step, the burden of proving this advantage or effect to the required standard of proof is on the patent proprietor. The mere assertion in the patent specification of an advantage or effect cannot be regarded as evidence of such an assertion.
The board listed a number of decisions (T 97/00, T 355/97, T 1097/09, T 1392/04), in which the underlying circumstances were comparable, confirming these principles. The board also observed that T 1797/09 submitted by the patent proprietor remained a singular decision not followed. The subject-matter of claim 1 of auxiliary request 1 lacked inventive step.