Art. 117(1) EPC does not contain an exhaustive list of admissible evidence, only mere examples. Parties to the proceedings are thus free in their choice of evidence. Similarly, the EPC does not foresee that certain questions of fact may only be proved by certain forms of evidence. Questions of fact must be settled on the basis of any credible information available (see e.g. J 11/88, OJ 1989, 433). For instance, what was common general knowledge on the date of filing of a patent application may be furnished in connection with an admissible request for correction under R. 139, first sentence, EPC (former R. 88, second sentence, EPC 1973) in any suitable form allowed by the EPC and may thus be based upon means of evidence in other than document form (G 11/91, OJ 1993, 125; cf. G 3/89, OJ 1993, 117).
Any kind of evidence, regardless of its nature, is admissible during proceedings before the EPO. Accordingly, the boards of appeal have admitted to the proceedings evidence obtained from witnesses or experts in accordance with R. 117 EPC (former R. 72 EPC 1973) as well as documents of any kind, including affidavits and statutory declarations. (see T 117/86, OJ 1989, 401; T 416/87, OJ 1990, 415; T 323/89, OJ 1992, 169; T 314/90). However, the admissibility of evidence should be clearly distinguished from the weight of evidence: whereas admissibility involves the question whether a piece of evidence should be considered at all, the probative value of evidence refers to the question whether the evidence to be considered provides sufficient proof of the alleged facts (see in detail under point 4.2. "Probative value of evidence").