In 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 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 determine 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, 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 and included claims 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 in the prior art and the distinctive features were difficult to pick out in a simple and unambiguous form.

In T 121/06 the board found that the combination of features in claim 1 was not known from the prior art. It would thus be detrimental to the logic of the claim to split up its features (i) to (iii) into their basic building blocks merely to indicate which blocks happen to be known from the prior art, without having regard to their inter-relationships. Thus, the two-part form of the claim was found to be inappropriate (R. 29(1) EPC 1973).

For further instances in which a claim in two-part form was not regarded as appropriate, see inter alia T 345/89, T 378/92, T 723/93 and T 181/95.