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. Any kind of evidence is admissible during proceedings before the EPO.
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).
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).
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 e.g. T 1698/08 on the distinction between admission of evidence and probative value of a document, and T 838/92 about a witness).
In T 1710/12, in the board's view, Art. 117(1) EPC gives no order of preference regarding the means of giving or obtaining evidence in proceedings before the EPO and it remains the free choice of a party to rely on the hearing of a witness (Art. 117(1)(d) EPC) EPC or on production of a sworn statement in writing (Art. 117(1)(g) EPC).
The board in T 885/02 observed that the opinion of an expert does not necessarily reflect the view of the skilled reader for various reasons. Those experts who were in the case at issue eminent scientists had their own experience which was not necessarily common general knowledge. Those observations did not mean that those declarations were to be disregarded.