Art. 101(1) EPC (Art. 101(2) EPC 1973) reinforces the right to be heard laid down in Art. 113 EPC by requiring the opposition division, when examining an opposition, to invite the parties "as often as necessary" to comment, within specified periods, on its own communications or those filed by other parties. Where necessary, any communication to the proprietor of the European patent must contain a reasoned statement covering all the grounds against the maintenance of the European patent (R. 81(3) EPC; R. 58(3) EPC 1973).

Art. 101(1) EPC does not require as a rule that the grounds for not maintaining the patent invariably be set out in a communication, but only if this is "necessary". Such "necessity" can arise only in efforts to establish the facts or in view of Art. 113(1) EPC. So the opposition division must issue a communication only if it considers this necessary, e.g. to take up new substantive or legal arguments or draw attention to points still requiring clarification. R. 81(3) EPC, which merely contains instructions concerning the content of any communications that may have to be issued, adds nothing to the above consideration of principle. Accordingly, the provisions of Art. 101(1) EPC and R. 81(3) EPC cannot be interpreted as meaning that the opposition division is obliged in every case to issue at least one communication before giving its decision, unless it is necessary to do so on the basis of Art. 113(1) EPC (see e.g. T 275/89, OJ 1992, 126; T 538/89, T 682/89 and T 532/91).

Not issuing at least one communication under Art. 101(1) EPC cannot in itself substantiate an allegation of infringement of the right to be heard under Art. 113 EPC (see e.g. T 774/97 and T 781/08). In T 165/93, for example, the board saw no need under Art. 113(1) EPC for the opposition division, before revoking the patent, to announce its opinion in a communication or to give a further opportunity to the patentee to declare whether he was interested in a limited patent if, despite having been informed of an additional objection of the opponent, he did not react but maintained his sole request for maintenance of the patent with the amended claims. Nor is it necessary under Art. 113(1) EPC to give a party a repeated opportunity to comment on the argumentation of the EPO body, so long as the decisive objection against the contested procedural action remains the same (see e.g. T 161/82, OJ 1984, 551; T 621/91).

According to T 295/87 (OJ 1990, 470), in opposition proceedings, under Art. 101(2) and R. 57(1) EPC 1973 (Art. 101(1) and R. 79(1) EPC) the proprietor has a right to file observations upon a notice of opposition. Thereafter, observations from the parties are only admissible in the exercise of the discretion of the opposition division or a board of appeal, if such observations are necessary and expedient in the sense of Art. 101(2) and R. 57(3) EPC 1973 (Art. 101(1), R. 79(3) EPC). The board specified that following communication of the patentee's observations (and any amendments), other parties are only to be invited by the opposition division to reply to such observations "if it considers it expedient". It was clearly desirable in the interest of the smooth and efficient conduct of opposition proceedings, and in the public interest, that observations by parties should be properly limited to what is necessary and expedient. This in turn required the exercise of a proper control by the opposition division (and by a board of appeal). Of course, the extent to which further observations are necessary or expedient depended upon various factors, including the complexity of the issues, and could only be decided in the context of each case. Nevertheless, in appropriate cases, the opposition division and the boards of appeal had the power, and indeed the duty, to refuse to admit observations and/or supporting documents for consideration, in the exercise of discretion under Art. 101(2) EPC 1973 and Art. 114(2) EPC 1973 and R. 57(3) EPC 1973 (Art. 101(1) EPC and Art. 114(2) EPC and R. 79(3) EPC).

For cases where a communication was, however, considered necessary, see in this chapter IV.C.6.5. below (T 293/88, T 120/96 and T 1056/98).