Art. 117(1)(g) EPC provides for sworn statements in writing as a means of evidence (rare in practice). However, since any kind of evidence is admissible in proceedings before the EPO, other, less solemn types of written statement (common in practice), e.g. statutory declarations, are also accepted. It is for the boards then to assess their probative value on a case-by-case basis. Such declarations consist of a witness's written statement, the main purpose of which is to avoid the need to hear that witness. The board may, however, decide to order such a hearing, for example if a party so requests. The terminology used in the case law includes "affidavits", "statutory declarations" and "unsworn statements" (French: "déclarations écrites", "déclarations sur l'honneur" and "attestations"; German: "eidesstattliche Versicherungen" and "eidesstattliche Erklärungen").
According to the practice of the boards of appeal, affidavits or statutory declarations, whether in original or copy form, are considered as possible means of providing evidence. One purpose of written declarations is to avoid the need to hear the undersigning person as a witness. Where such declarations consist of answers to questions put forward by legal experts several declarations may have certain stereotyped formulations in common. The board is not obliged to check the signatures as long as no counter-opinion has been presented concerning those signatures (T 674/91; see also T 558/95). In T 474/04 (OJ 2006, 129), where one party invoked T 674/91 to justify not having to hear the author of an unsworn witness declaration ("eidesstattliche Versicherung") as a witness, the board pointed out that the case before it was different in that the fundamental assertions made in the declaration were contested, the author had been offered as a witness, and the appellant had consistently demanded that he be heard. The opposition division's decision not to summon him as a witness although he was available had handicapped the appellant in its defence against what turned out to be the decisive piece of evidence. It was observed that this piece of evidence largely lay "within the power and knowledge of the opponent".
Written statements by potential witnesses or parties typically have a lower probative value than oral evidence taken by the department deciding on the case. If a disputed point is highly relevant to the validity of the contested patent, it is, as a rule, not in keeping with good procedural practice for an opposition division not to take up an opportunity to hear a witness or party in evidence and instead to require written statements and make do with their typically lower probative value. The board in T 329/02 could not identify any extraordinary circumstances that might have justified an exception to this rule in the case in point.
In T 918/11, the board found that it went against the general rules concerning the consideration of evidence to distinguish dogmatically between the evidentiary value of a witness testimony on the one hand and a document on the other hand. The opposition division had apparently considered documents to be of a more conclusive evidentiary value than witnesses. Such an approach had no basis in the EPC, Art. 117 EPC containing no ranking of the therein listed means of evidence.
Sworn statements in writing, one of the means of giving evidence listed in Art. 117(1) EPC, are not automatically ordered simply at the request of one party. All the means of giving or obtaining evidence covered by Art. 117 EPC are subject to the discretion of the department concerned, which will order their use only if it considers this necessary (T 798/93, OJ 8/1997, 363).
The board may consider an affidavit to be admissible evidence even if it is signed by the general manager of the appellant (see T 327/91). In T 2003/08 (reported in this chapter) the board observed that relations with the appellant's (opponent's) company could possibly have influenced Dr W's and Dr K's objectivity concerning their declarations ("Eidesstattliche Versicherung"). The board considered that its reservations concerning declarations E1 (declaration of Dr W, lecturer) and E2 (declaration of Dr K, member of the audience) could possibly be dispelled by hearing the authors of declarations E1 and E2 themselves.
Sworn statement (Art. 117(1)(g) EPC) are to be distinguished from "statutory declarations", which are not given on oath. Albeit not explicitly covered by Art. 117(1)(g) EPC, statutory declarations are regarded as admissible means of evidence and are taken into account in accordance with the principle of the unfettered consideration of evidence (see e.g. T 770/91, J 10/04 and T 535/08).
A statutory declaration ("eidesstattliche Erklärung" or "déclaration tenant lieu de serment") is a means of giving evidence within the meaning of Art. 117(1) EPC and as such is subject to the principle of free evaluation of evidence (T 558/95, cf. T 482/89, OJ 1992, 646, point 2.1 of the Reasons; T 575/94, point 3.7 of the Reasons). The board in T 443/93, which had French as the language of the proceedings, referred to a document entitled "eidesstattliche Erklärung" alternately as a "déclaration sous serment" (affidavit) and a "déclaration écrite" (written statement); T 563/02 referred to a document entitled "affidavit" as "déclaration sur l'honneur". The board in T 474/04 (OJ 2006, 129), which had English as the language of the proceedings, referred to a document entitled "eidesstattliche Versicherung" as a "declaration in lieu of an oath" and an "unsworn witness declaration". In T 703/12, the board called a document of this kind entitled "eidesstattliche Versicherung" a "statutory declaration" and in T 1231/11 an "affidavit". In proceedings before the EPO even a simple declaration can be an admissible means of evidence within the meaning of Art. 117(1) EPC (T 474/04, OJ 2006, 129 – a decision establishing a number of points relating to the law of evidence). The EPO accepts unsworn solemn declarations the same way it accepts other unsworn statements (T 970/93, T 313/04).
In T 558/95, the board held that the fact that the statutory declarations produced by the opponent partly used the same wording and had been drawn up by employees of the opponent did not necessarily mean they should be excluded as inadmissible. The opposition division had discretion to decide whether to examine them, and to determine whether or not the evidence in them was sufficient.
In T 190/05, which contains extensive reasoning on the issue of evidence, the board ruled that, under R. 68(2) EPC 1973 (R. 111(2) EPC), the opposition division ought to have explained more clearly in the reasons for its decision why it had regarded the alleged prior use as substantiated and the statutory declaration as sufficient evidence. Neither the summons nor the brief communication, nor the minutes of oral proceedings, could substitute adequate reasoning in the decision.
In R 3/10 the Enlarged Board took signed declarations of persons who had attended the oral proceedings into account.
On the probative value of witness testimony and written statements, see also in this chapter III.G.4.2.1.