Where lack of novelty is alleged, the burden of proof invariably lies with the party claiming that the information in question was made available to the public before the relevant date (see, for example T 193/84, T 73/86, T 162/87, T 293/87, T 381/87, OJ 1990, 213; T 245/88 and T 82/90). According to the boards' established case law, each of the parties to the proceedings bears the burden of proof for the facts it alleges. If a party, whose arguments rest on these alleged facts, does not discharge its burden of proof, this is to the detriment of that party, who may not shift the onus of proof onto the other party (see T 270/90, OJ 1993, 725; T 355/97; T 836/02; T 176/04, T 175/09) (cf. T 443/09).
In decisions T 73/86, T 162/87, T 293/87, T 708/89, T 82/90, T 600/90, T 267/91, T 782/92 and T 34/94 the boards assumed that all the circumstances surrounding prior use must be proved by the party raising the objection.
In T 743/89 the board applied the principle of prima facie evidence. Here, it had been proved that a leaflet disclosing the invention had been printed seven months before the date of priority, but it was uncertain when the leaflet had been distributed. The board took the view that, although the date of distribution could no longer be ascertained, it was reasonable in any event to assume that distribution had occurred within the seven-month period. The respondents contended that this was not the case, but the board considered this assertion to be so lacking in plausibility that it placed the onus of proof on the respondents.
Ruling on an objection of prior public use in T 221/91, the board held that it was for the patent proprietors to prove the existence of an obligation to maintain secrecy when the opponents had proved that the invention had been made available to the public and the patent proprietors had claimed the existence of a secrecy agreement (see also T 969/90 and T 1054/92).
In T 901/95 the board decided that merely claiming that generating equipment was installed into ships at three different shipyards and thus available to the public was not enough to demonstrate its obvious prior use. Shipyards were normally considered restricted areas and thus not open to the general public. This applied all the more to installations built into ships in the yards. Nor could the possibility be excluded that shipyards' business partners might secure their common interests through explicit or tacit secrecy agreements, in the absence of other protection. In the case in point, it was also questionable whether the relevant process steps and the functional arrangement of the switching means were apparent from merely looking at built-in apparatus; nor was it certain when the generating installations had become operational. Both parties dispensed with oral proceedings and no witnesses were heard; the board did not in these circumstances consider the alleged public prior use.
In T 887/90 the obligation to maintain secrecy was derived from the circumstances. In this case the board's view was that the onus for proving the contrary lay entirely with the opponents. (similarly T 541/92; see also Chapter III.G "Law of evidence").