According to the established case law of the boards of appeal, determining unity of invention requires as a precondition an analysis of the technical problem or problems underlying the respective group of inventions (see W 11/89, OJ 1993, 225; W 6/97, T 188/04), i.e. whether or not the subject‑matter claimed as the solution to such a problem represents a single general inventive concept (see W 6/91; also T 2248/12 and T 129/14). The disregard of this principle would be in itself sufficient justification for the reimbursement of the additional search fees. In W 8/94 the board held that a discussion of the problem underlying the claimed subject-matter was required, because only then was it possible to decide whether or not a common special technical feature within the meaning of R. 13.1 and R. 13.2 PCT existed for different embodiments (see W 11/89, OJ 1993, 225; W 14/89, W 59/90, W 14/91, W 17/91).

In W 6/97 the board found that establishing the technical problem underlying a claimed invention or group of inventions in relation to the state of the art should start, as a rule, from what was considered in the description as having been achieved by the claimed invention, since claims directed to compositions of matter at least were normally silent on the technical effects to be achieved by such compositions. As soon as the search revealed prior art which was clearly more relevant than that already acknowledged in the description of the international application, it was necessary to determine what was to be considered as the particular technical problem in view of both the disclosure of the international application as a whole and the prior art thus revealed (see W 6/91). Unity of invention might be assessed only after the technical problem had been determined in such a manner.

The boards have on several occasions stressed that an alleged lack of clarity in a claim cannot be used as a reason for an objection based on lack of unity (see W 31/88, OJ 1990, 134; W 7/89, W 59/90, W 9/02). In W 21/04 the board observed that according to the established case law of the boards of appeal the features of an independent claim that the ISA held not to meet the requirements of Art. 6 PCT could not be disregarded in examining a lack of unity objection.

In W 17/03 the board was concerned with the investigation of technical relationships for unity. The case is summarised in this chapter II.B.4.2. below.