Claims lack clarity if the exact distinctions which delimit 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; T 1253/11; T 355/14). The Enlarged Board held in G 1/04 (OJ 2006, 334) that the meaning of the essential features should be clear for the person skilled in the art from the wording of the claim alone (see also T 342/03, T 2091/11, T 630/14, T 1140/14, T 1957/14). 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 (see in this chapter II.A.6.3.).

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 (see also T 1399/11). 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.

In T 586/97 the main claim was directed to an aerosol composition comprising a propellant and an active ingredient which was not defined. The board held that, when an essential ingredient comprised in a chemical composition is open to be labelled arbitrarily "active ingredient" or not, the meaning of that feature would be variable. Leaving the public in doubt as to which compositions are covered by the claim would be at variance with the principle of legal certainty. Therefore, the claim at issue failed to meet the requirement of clarity imposed by Art. 84 EPC 1973. See also T 642/05, T 134/10.

In T 1045/92 the claims concerned "a two-pack type curable composition comprising [...]". In the board's view "a two-pack curable composition" was an item of commerce as familiar to readers skilled in the polymer art as everyday articles were to the public at large. The claim was therefore clear.

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 268/13 the board concluded that a claim to a "method for producing a [...] decorative strip having a [...] structure consisting of a text or graphic symbol [...]" satisfied the requirements of Art. 84 EPC 1973. Although it was impossible to give an entirely general, universally applicable definition of what constituted a symbol, in the case in hand it would be clear whether or not a particular character was a symbol in the given cultural, linguistic or technical context. The claim therefore presented neither somebody wanting to avoid infringing the patent nor a court deciding on infringement with an impossible task.

In T 1957/14 the board was not persuaded by the appellant's argument that deposited material serves as a surrogate for the description of a sequence, i.e. as an alternative to structural information. In the board's opinion, relying on deposited inbred line material for the definition of the essential features of the invention and requiring it to be analysed in order to identify the relevant alleles was at odds with the principle that, generally, the meaning of a claim, including its essential features, should be clear for the person skilled in the art from the wording of the claim alone.

In T 1845/11 the board concluded that the term "Asian race" was not clear. Clearly defined objective criteria for patient assignment into racial groups were not available to the skilled person.

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, T 127/04). In T 1534/10 a claim contained the feature "that the data carrier (1) is constructed in a multi-layered manner as a laminate and contains at least two films (4, 5) which are integrated as a cover film (4) or as a core film (5) into the layer construction of the laminated data carrier". The board considered this wording ambiguous because it combined a plural form ("at least two films (4, 5)") with a singular form ("as a cover film (4) or as a core film (5)"), making it unclear whether the "at least two films" were each either a cover film or a core film, or whether together they formed a new film that was then either a cover film or a core film.

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, see also chapter II.C.8.1. "Art. 83 EPC and support from the description").

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, T 270/11; see also chapter II.E.1.7.3 e) "Drafting of disclaimers – clarity"). 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.

In T 75/09 the board held that where higher ranking requests are refused because a feature common to all requests does not meet the requirements of Art. 84 EPC, all lower ranking requests retaining this feature have to be refused for the same reason.