Art. 113(1) EPC, in which the right to be heard is enshrined, provides that decisions of the EPO may only be based on grounds or evidence on which the parties have had an opportunity to present their comments. The term "grounds or evidence" in Art. 113(1) EPC should not be narrowly interpreted. The word "grounds'' does not refer merely to a ground of objection to the application or patent in the narrow sense of a requirement of the Convention which is considered not to be met. The word "grounds" should rather be interpreted as referring to the essential reasoning, both legal and factual, which leads to the findings of the decision (see e.g. T 951/92, OJ 1996, 53, with regard to a refusal of the application, T 433/93, with regard to the finding of invalidity and revocation, and T 1056/98 with regard to inadmissibility; on the right to be heard, see also chapter III.B.).

In T 293/88 (OJ 1992, 220) the board found that the decision of the opposition division to revoke the patent without issuing any communication in advance disregarded the fact that the validity of the uncontested claims 7, 9 and 10 had not been challenged at all, and a further opportunity to fall back at least to such position was reasonably to be expected in such circumstances. The onus of raising such related additional matter with the parties was on the opposition division under Art. 113(1) EPC – which it had not done in this case.

In T 558/95 the opposition division had issued two written communications before the oral proceedings stating that, "in the provisional opinion of the opposition division", the subject-matter described in the public prior use did not prejudice the contested patent within the terms of Art. 100(a) EPC. The patent proprietor therefore found it "surprising" that detailed consideration was given to the public prior use during the oral proceedings. However, the board held that provisional opinions of this kind were not binding on the further proceedings. Especially in view of the fact that the opponent continued to elaborate his arguments against these comments by the opposition division, the possibility of a different assessment by the opposition division could not be ruled out from the start.

The opposition division that rejects an opposition as inadmissible without providing a reasoning prior to its decision prevents the opponent from responding with comments, thus violating the right to be heard (T 1056/98).

Normally, where a document has been sent to one of the parties, that party is given sufficient time to respond thereto before a department of the EPO takes a decision (T 263/93). If the case is to be remitted to the department of first instance for further prosecution, the recipient of a document still has, in view of the remittal, the opportunity to contest the arguments put forward by the other party (see T 832/92).

Under Art. 113(1) EPC, the opposition division must expressly give the parties an opportunity to present observations after remittal to it of a case by a board of appeal for further prosecution on the basis of new evidence, even if submissions with respect to this new evidence have already been made during the preceding appeal proceedings (see T 892/92, OJ 1994, 664; see also T 769/91). In T 120/96 another board shared this view and added that the term "opportunity" in Art. 113(1) EPC could only be given effective meaning by applying the principles of good faith and the right to a fair hearing. For such an opportunity to exist, it is necessary that the parties be expressly asked whether or not they wish to present, within a fixed period of time, their comments, or if, as in the case at issue, the parties have already made detailed submissions during the previous appeal proceedings, whether or not these submissions should be regarded as complete. On these grounds alone, the board found that the immediate termination of the opposition proceedings following the remittal, without any intervening communication announcing the resumption of proceedings, was inconsistent with Art. 113(1) EPC.

In T 1027/13, a case in which an accompanying person had not been allowed to speak in oral proceedings before the opposition division, the board held that an effective and efficient conduct of oral proceedings, although subject to the discretionary power exercised by the chairman in oral proceedings with regard to specific issues, must nevertheless guarantee that the fundamental procedural rights of each party in adversarial proceedings, i.e. the right to fair and equal treatment, including the right to present comments in oral proceedings (Art. 113(1) and 116 EPC), are respected. The board concluded that the categorical refusal of the opposition division that the accompanying person may make oral submissions or even communicate with the opponent's representative in effect had been keeping the opponent from taking position in an "efficient and effective manner" on the contentious issues of the case (see also chapter III.V.5.2.).