A claim may be limited by inclusion of additional features, provided the resulting combination was originally disclosed and does not relate to an invention which was not searched (Guidelines H-V, 3).
In T 708/00 (OJ 2004, 160) the board held that under R. 86(4) EPC 1973, amended claims could only be refused if the subject-matter of the claims filed originally and that of the amended claims was such that, had all the claims originally been filed together, a further search fee would have been payable - on top of the search fees payable in respect of the claims actually filed at the outset - in respect of the amended claims, relating to a different invention within the meaning of R. 46(1) EPC 1973 (see also T 319/96 and T 631/97, OJ 2001, 13). It noted that "a subsequent amendment to limit the subject-matter of the main claim by additional features disclosed in the application as filed did not generally affect the notion of unity of invention under either R. 86 (4) or 46 (1) EPC 1973" and that "it is normal for an applicant to make such an amendment in respect of an objection to the patentability of the subject-matter in unlimited form" (T 2334/11).
In T 274/03 it was however made clear that certain conditions have to be satisfied for an amendment not to generally affect the notion of unity of invention. Thus, this notion is not affected, and therefore no post-search switching of subject-matter is involved by the amendment, if for instance features are added from the description to further define an element that was already a feature of the original main claim, to further specify an essential aspect of the original main claim (see T 1394/04).
In T 2334/11, the board held that what generally had to be ascertained for the purposes of applying R. 137(5) EPC where an original claim was amended by adding a feature was whether the added feature could be regarded as falling under the original general inventive concept as established in the light of the claims and description as filed (see T 1640/07), and not whether the originally claimed subjectmatter and the subjectmatter defined in the amended claim withstood an assessment of unity a posteriori. It found that one of the ideas underlying the case law on application of R. 137(5) EPC was that, while amendments to claimed subjectmatter which considerably altered the essence or nature of the invention - especially through replacement or omission of features in a claim (see T 442/95 and T 274/07) might occasion an objection under R. 137(5) EPC, the mere limitation or the more specific drafting or supplementing of a claim by inclusion of a feature disclosed in the application as filed, in order, for example, to overcome an objection of lack of clarity, novelty or inventive step, generally did not result in a lack of unity with the originally claimed invention for the purposes of R. 137(5) EPC (see also Guidelines C-VI, 5.2(ii), first paragraph).
In T 1394/04 the board noted that careful consideration of the very nature of the added feature is necessary in order to determine whether the amendment leads to a situation where lack of unity of inventive concept between the original main claim and the later claimed subject-matter arises. Such a situation in the context at issue would necessarily entail an implicit finding of lack of unity "a posteriori" (T 274/03, point 6 of the Reasons) and according to the Guidelines for examination (C-III, 7.7) in the EPO this form of objection to lack of unity should be the exception. The board also noted that it could not be excluded that such a situation could arise as a consequence of later amendments supported solely by the description. In fact, it may occur that the description of the application contains a further general inventive concept, distinct from that underlying the main claim and its dependent claims, if any, but not clearly identified or declared as such in the description. In such a case, if the subject-matter of the main claim based on the first inventive concept had to be amended, on account of a lack of novelty resulting from too broad terms used in the wording, any amendment of the claim pertaining exclusively to said further inventive concept could justify an objection of lack of unity "a posteriori". This example elucidates that situations may actually occur where the amendment of the main claim, whose subject-matter lacks novelty, based on features supported exclusively by the description, may affect the notion of unity of the invention. Although such situations occur very rarely in practice, as already noted above, in such cases R. 86 (4) EPC would have to be applied in order to avoid a possible circumvention of Art. 82 EPC. In the case at issue however it was clear that, much the same way as in the decision T 274/03, the introduced amendment feature merely constituted a further specification of original features of the claim which are essential to the invention. This constituted an essential aspect of the invention. Therefore, no lack of unity pursuant to R. 86 (4) EPC 1973 in conjunction with Art. 82 EPC 1973 could be found.