Claims lack clarity if the exact distinctions which delimited the scope of protection cannot be learnt from them (T 165/84, T 6/01). The claims per se must be free of contradiction (see T 2/80, OJ 1981, 431). They must be clear in themselves when read by the person skilled in the art, without any reference to the content of the description (T 2/80, T 1129/97, OJ 2001, 273; T 2006/09).
The description is taken into account for the purposes of interpreting the claims and has in some cases also been considered when determining clarity and conciseness. The reader is referred to point 6.3.5 below in relation to case law thereon.
When a claim is directed to a product characterised by parameters, those parameters must be clearly and reliably determined (see point 3.5 below).
In the key decision T 728/98 (OJ 2001, 319) the board held that it followed from the requirement of legal certainty that a claim could not be considered clear within the meaning of Art. 84 EPC 1973 if it comprised an unclear technical feature (here “substantially pure”) for which no unequivocal generally accepted meaning existed in the relevant art. This applied all the more if the unclear feature was essential for delimiting the subject-matter claimed from the prior art. Likewise in T 226/98 (OJ 2002, 498) the board held that the feature "as a pharmaceutical product" for defining a pharmaceutical standard of purity in a claim related to a product as such (here, famotidine form "B"), rendered said claim unclear in the absence of a generally accepted quantitative definition for the purported standard of purity.
When an essential ingredient comprised in a chemical composition is open to be labelled arbitrarily "active ingredient" or not depending exclusively on the mental label the user wished to apply, thereby rendering the meaning of that feature variable, then the public is left in doubt as to the distinction which compositions are covered by the claim and which are not, which is at variance with the principle of legal certainty. Because of that lack of legal certainty, the claim at issue in T 586/97 failed to meet the requirement of clarity imposed by Art. 84 EPC 1973 (see also T 642/05 and T 134/10).
In T 390/08 the board held that the definition of a composition as "consisting of" compulsory and optional components met the requirements of Art. 84 EPC, as such a composition defined a "closed" composition from which elements other than those mentioned were excluded (see also T 1190/01 and T 1998/07).
In T 651/05 the board found that the introduction of vague terms created a lack of clarity due to different but equally valid interpretations (see also T 621/03 and T 127/04). Where, on one of several possible constructions of a vaguely formulated claim, part of the subject-matter claimed is not sufficiently described to be carried out, the claim is open to objection under Art. 100(b) EPC 1973 (T 1404/05, also reported under II.C.7.1, Art. 83 EPC and support from the description).
In decisions T 1129/97 (OJ 2001, 273) and T 274/98 the board emphasised that, to satisfy the clarity requirement, the group of compounds/ingredients according to the claim had to be defined in such a way that the skilled person could clearly distinguish compounds/ingredients that belonged to the claimed group from those that did not (see also T 425/98 regarding the expression "consisting of a major amount of").
In T 762/90 a lack of clarity was found in the use of a trade mark designating a whole series of products which differed from one another depending on phases in their industrial development. Moreover, the board expressed doubts about the use of such a designation, since it was uncertain whether the meaning of the trade mark would remain unaltered up to the end of the patent term (see also T 939/92). Similarly, in T 480/98 the board considered that a trade mark product referred to in the characterising portion of claim 1 did not have a clear technical meaning, in that it could refer to a plurality of products having different compositions and properties. In consequence there was a lack of clarity, and the claim was not allowable. According to the board in T 623/91 the exclusion of a composition by reference to the trade mark or trade designation would not introduce uncertainty and therefore not offend against Art. 84 EPC 1973, as changes in the range of chemical composition would not be likely without a corresponding change in the trade name or trade mark.
The preamble of claim 2 of the application in T 363/99 contained a reference to a German patent specification. The board considered this to be a violation of Art. 84, second sentence, EPC 1973 since it was impossible to establish the scope of the matter for which protection was sought without consulting the reference document mentioned. The fact that the indication of the publication number of the reference document provided the most concise definition of the matter for which protection was sought (Art. 84 EPC 1973) was irrelevant by comparison. When formulating a patent claim, the form that was objectively more precise always had to be chosen (T 68/85, OJ 1987, 228).
Complexity as such is not equivalent to a lack of clarity - clarity under Art. 84 EPC is not at stake in a case of mere complexity of a claim provided the subject-matter for which the protection is sought and the scope thereof are clear and unambiguous for a person skilled in the art, either per se or in the light of the description (see T 574/96 re Art. 84 EPC 1973). In T 1020/98 (OJ 2003, 533) the board confirmed that compliance with the clarity requirement of Art. 84 EPC 1973 was not dependent on the time required to establish whether a given compound was covered by the product claim. The clarity requirement was not a basis for objecting to the complexity of a claim. Clarity within the meaning of that article merely required the claims to define the subject-matter for which protection was sought clearly and unambiguously for the skilled person, if necessary in the light of the description.