The opposition division will first of all endeavour to reach a decision in written proceedings. Taking account of the investigations usually conducted beforehand by the primary examiner (see D‑II, 5 and D-II, 6), the opposition division will base its decision on the written submissions of the parties and, where appropriate, on other written evidence obtained, in particular, through the production of documents, requests for information and sworn statements in writing.

The parties in inter partes cases are subject to a particular duty to facilitate due and swift conduct of the proceedings, in particular by submitting all relevant facts, evidence, arguments and requests as early and completely as possible (see D‑IV, 1.2.2.1, and E‑IV, 1.2). Furthermore any ground, fact and evidence filed by the opponents after the expiry of the opposition period are considered as late-filed unless they are due to a change in the subject of the proceedings; see E‑VI, 2, and E‑VI, 2.1, for more details. Admissibility of amendments by the proprietor is treated in detail in H‑II, 3, to H‑II, 3.5.[Art. 114(2); Rule 76(2)(c); Rule 80; ]

If the opposition division considers it expedient, or if any party requests oral proceedings, oral proceedings in accordance with Art. 116(1) will be held before the opposition division after suitable preparation (see D‑VI, 3.2). In the oral proceedings, the parties may state their cases and make submissions in order to clarify outstanding questions. Members of the opposition division may put questions to the parties.[Art. 116; ]

In special, less common cases it will occasionally prove necessary in opposition proceedings for oral evidence to be taken by the opposition division as part of oral proceedings or for the conservation of evidence, or by the primary examiner outside the oral proceedings. The opposition division is not obliged to take oral evidence if it does not consider it necessary, even if a party has so requested. Oral evidence may be taken, where appropriate under oath, before the competent court in the country of residence of the person to be heard. A member of the opposition division may, at the request of the opposition division, attend such court hearings (see E‑IV, 1.3).[Rules 117; Rule 120; ]

The principal means of taking oral evidence will be the hearing of witnesses and parties (see E‑IV, 1.6).

Only in exceptional cases will evidence be obtained at the initiative of the opposition division by means of oral and/or written reports by experts (see E‑IV, 1.8.1) or by carrying out an inspection (see E‑IV, 1.2, last paragraph). In view of the specialised knowledge of the members of the opposition division – and of the costs involved – such means will be used only as a last resort.