1.2 Means of evidence 

The party or parties may submit evidence in support of alleged facts at any time during proceedings (see E‑III, 5, E‑X, 1.2E‑IX, 1.2, D‑IV, 5.3, D‑IV, 5.4 and D‑VI, 3) but must do so at the earliest opportunity. When new evidence could have been put forward at an earlier stage, it is for the competent department to consider whether it is expedient to admit it (see E‑VI, 2).

It is generally desirable for parties to produce evidence for all the facts alleged in support of their case, e.g. to show whether a particular technique was generally known in industry or whether there was any prejudice against a particular technique.

However, facts alleged by a party will normally be deemed true, even without supporting evidence, if there is clearly no doubt about them, if they do not contradict one another or if they are not contested. In such cases, they need not be supported by evidence.

There will nevertheless be times, particularly in opposition proceedings, when the arguments of the party or parties must be supported by evidence. This will, for example, be the case where reference is made to prior art, for instance in the form of an oral description, a use or perhaps a company publication, and there is some doubt as to whether, and if so when, this prior art was made available to the public.

The means of evidence which are admissible in proceedings before the EPO are (non-exhaustively) listed in Art. 117(1):

– production of documents 

– hearing the parties 

– hearing witnesses 

– sworn statements in writing 

– requests for information, for instance from a publisher concerning the date of publication of a book 

– opinions by experts (see E‑IV, 1.8.1) and

– inspection. 

The most appropriate way of obtaining evidence in the individual case depends on the facts which have to be proven and on the availability of the evidence. To prove prior use in opposition, the opponents usually offer to produce documents or suggest hearing witnesses or parties, or they present sworn statements in writing. It is at the opposition division's discretion to evaluate this evidence and there are no fixed rules on how the various categories of evidence are to be assessed (on evaluating evidence, see E‑IV, 4).

If the documents produced (e.g. patent documents) leave no doubt as to their contents and date of availability to the public and are more relevant for the patent in suit than other evidence offered, reasons of procedural efficiency may lead the opposition division to leave the other evidence aside at first.

If the testimony of a witness is offered, the opposition division may decide to hear this person in order to verify the facts for which they are brought forward, e.g. the prior use of the claimed product in an undertaking or the existence of an obligation to maintain secrecy. For adequate substantiationIn order to be adequately substantiated, the notice of opposition must set make clear these facts out clearly, as witnesses are meant to corroborate alleged facts, not to supply these facts in the opponent's place. The same applies to hearing the parties (see also E‑IV, 1.6).

The "sworn statements in writing" referred to in Art. 117(1)(g) are unknown in some national legal systems, which instead have their own instruments (see T 558/95).

Whether a written statement ("affidavit") is made under oath or not is only one of the criteria applied by the opposition division in its evaluation of the evidence adduced. Apart from its relevance for the case, other criteria are the relationship between the person making the statement and the parties to the proceedings, the personal interest of that person, the context in which the statement was made, etc. Such a statement does not go beyond its literal content and does not allow the opposition division to assess the associated or background factors. If the alleged facts are contested by the other party, the opposition division generally does not base its decision on such a statement but, if so offered by the party, instead summons the person making it as a witness. The subsequent hearing of the witness allows the opposition division and the parties to ask them questions and so enables the opposition division to establish the facts on the basis of their testimony. If the person is not offered as a witness, the opposition division will not consider this evidence any further.

Inspection will enable direct observations to be made and direct impressions to be formed of the object or process concerned. It may, for example, involve the demonstration of a product or process requested by the applicant or proprietor of the patent to substantiate the method of operation of the subject-matter of the patent where this is disputed by the examining or opposition division.

Evidence in the form of documents normally stays on the file. Only exceptionally and on reasoned request can documents filed as evidence be returned unconsidered, e.g. if they were third-party statements filed in breach of a confidentiality agreement and the other parties agree to the request (see T 760/89).