1.2 Means of evidence 

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

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

Facts adduced by a party will, however, normally be deemed true, even without supporting evidence, if it is clear that no doubts exist concerning them, if they do not contradict one another or if no objection is raised. In such cases the facts need not be supported by evidence.

There will however be occasions, particularly in opposition proceedings, in which 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, such 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 an opposition, the opponents usually offer as evidence the production of documents, the hearing of witnesses or parties, or they present sworn statements in writing. It is at the opposition division's discretion to evaluate this evidence, there being no fixed rules as to how any category of evidence is to be judged (for the evaluation of 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 not pursue the other evidence 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 this witness is brought forward, e.g. the prior use of the claimed product in an undertaking or the existence of an obligation to secrecy. For adequate substantiation the notice of opposition must make clear these facts, as witnesses are meant to serve for corroboration of facts brought forward, not for supplying these facts in place of the opponent. The above applies likewise 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 does not generally base its decision on such a statement, but summons the person making the statement as a witness, if so offered by the party. The ensuing hearing of the witness allows the opposition division and the parties to put questions to the witness and thus enables the opposition division to establish the facts on the basis of that person's testimony. If that person is not offered as a witness, the opposition division will not pursue this evidence 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).