While the boards are not obliged to provide the parties in advance with all reasons for a decision in detail (see in this chapter IV.F.3.13.5), Art. 113(1) EPC requires that decisions may only be based on grounds or evidence on which the parties concerned have had an opportunity to present their comments, which implies that a party may not be taken by surprise by the reasons of a decision, referring to unknown grounds or evidence (R 3/13; see also R 15/09, R 21/10). "Grounds or evidence" under Art. 113(1) EPC is understood as the essential legal and factual reasoning on which a decision is based (see Chapter III.B.2.3.2 "The meaning of 'grounds or evidence'"). In R 3/10, R 15/11 and R 16/13 the petition was allowed because of surprising reasons on which the parties had not been given an opportunity to comment (see in this chapter IV.F.3.13.19).
Grounds or evidence within the meaning of Art. 113(1) EPC need not emanate from the board, it is sufficient if another party raises the objection (R 2/08; see also R 1/08, R 1/13). If the reason given in a decision corresponds to an argument put forward by the other party, the petitioner was aware of it and thus not taken by surprise (R 4/08, R 12/09; see also R 8/14), unless the board clearly indicated that it regarded those arguments as not convincing (R 11/12).
A subjective surprise (in R 6/11, R 1/13: the petitioner's belief that the board would decide in its favour) has no bearing on whether a party knew the issues which might be raised and had an adequate opportunity to comment thereon (R 13/11, R 17/12; see, by way of example, also R 12/09, R 22/10, R 1/13, R 3/13).
To determine which subject matter (grounds, facts and evidence) could have been expected to be discussed, and whether new facts and grounds were introduced ex officio by a board of appeal in its decision, the Enlarged Board has to check the file history (R 8/13).
Establishing the closest prior art is part of the process of arriving at a decision and takes place only after all arguments have been heard, in the final deliberations of the board. If the closest prior art is redefined because of an amendment to a claim, the board is not obliged to address this at oral proceedings (R 8/14).
Dismissing a party's interpretation of a document in a decision in a way which does not introduce any change in the factual and legal framework of the debate does not infringe the right to be heard, in the same way as "arguments" can be put forward by a party in the absence of the other party, as stated in G 4/92 (R 2/13).
Several further cases in which the petitioner claimed that the decision under review took it by surprise were rejected by the Enlarged Board, stating that