8.2. Article 83 EPC and clarity of claims

If it is argued that insufficiency arises from a lack of clarity, it is generally not sufficient to establish a lack of clarity of the claims in order to establish lack of compliance with Art. 83 EPC 1973. Rather, it is necessary to show that the patent as a whole (i.e. not only the claims) does not enable the skilled person – who can avail himself of the description and his common general knowledge – to carry out the invention (see T 1811/13, T 646/13).

There is now a clearly predominant opinion among the boards that the definition of the "forbidden area" of a claim should not be considered as a matter related to Art. 83 and 100(b) EPC (T 1811/13, T 646/13). Decision T 626/14 does not call this into question, according to the board in T 250/15.

When undefined parameters are used in the claims and no details of the measuring methods are supplied, the question arises whether there is a problem with respect to Art. 83 or Art. 84 EPC. The answer to this question is important because in opposition proceedings the patent can be examined for its compliance with Art. 83 EPC without any restriction. Compliance with Art. 84 EPC is however examined only in cases where there has been an amendment. In its decision G 3/14 (OJ 2015, A102) the Enlarged Board reiterated the principles governing the extent to which patents amended in opposition proceedings can be examined for compliance with Art. 84 EPC. A more detailed account of its decision can be found in chapter II.A.1.4.

T 1845/14 (broadness of the claim arising from lack of clarity and sufficiency) specified that the ambiguous definition of a parameter in a claim may result in the scope of the claim to be broader than the patentee might have intended. In such a case the question arises whether the teaching of the patent in suit, which was directed to the claimed subject-matter having regard to a specific meaning of that parameter (which, however, was omitted), would nevertheless have enabled the skilled person to carry out the invention outside of the scope intended by the patentee, using common general knowledge and a reasonable amount of experimentation.