In decision T 13/84 (OJ 1986, 253), the board ruled that a claim in two-part form had to be regarded as appropriate if a clearly defined state of the art existed from which the claimed subject-matter distinguished itself by further technical features (likewise T 181/95). This decision was confirmed by T 162/82 (OJ 1987, 533), where the board added that the extent to which prior art was cited in the description could not be a determining factor in deciding whether the one-part or the two-part form of a claim was appropriate in a given case.
In T 170/84 (OJ 1986, 400) it was pointed out that where a two-part claim would lead to a complex formulation it was no longer appropriate. In a one-part claim, the features required for the definition which belonged to the state of the art had to be sufficiently clear from the description. This principle has been upheld inter alia in T 269/84, T 120/86, T 137/86 and T 278/86. The latter two decisions stipulated that a two-part claim was not justified if it gave an incorrect picture of the state of the art (likewise T 181/95). In T 735/89 the board did not accept a one-part claim because it gave the impression that there was no closer state of the art.
In T 99/85 (OJ 1987, 413) the board held that in opposition proceedings there was no reason officially to insist on a change in the wording of the claim simply because one feature in the preamble to a two-part claim did not belong to the state of the art. Furthermore, the board saw R. 29(1) EPC 1973 as an implementing regulation which did not constitute a ground for opposition (a similar view was held in T 168/85, T 4/87, T 429/88 and T 65/89).
In T 350/93 the patent application disclosed processes for the production of electro-active material and composite materials containing such material. It included main claims 1 to 4 and 6 to 8 in one-part form. The board observed that the one-part form was justified because details in certain process steps distinguished the claimed processes from those known from the prior art and the resulting distinctive features were difficult to pick out in a simple and unambiguous form.
In T 121/06 a new document, annexed to the communication under R. 51(4) EPC 1973, was introduced as the closest prior art. As a consequence, the examining division drafted the independent claims in two-part form based on the new document. On appeal, the board found that the combination of features in claim 1 was not known from the new document. It went on to state that it would be detrimental to the logic of the claim to seek to split up its features (i) to (iii) into their basic building blocks merely to indicate which blocks happen to be known from the new document, without having regard to their inter-relationships. Thus, the two-part form of claim was found to be inappropriate (R. 29(1) EPC 1973).