3.1. General principles

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; T 1089/19; T 1152/21). 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, T 2968/19). 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.6.2.2b) and II.A.6.2.3e)). In G 1/24 (OJ 2025, A60) the Enlarged Board highlighted the importance of the examining division carrying out a high-quality examination of whether a claim fulfils the clarity requirements of Art. 84 EPC and stated that the correct response to any unclarity in a claim was amendment (point 20 of the Reasons).

In T 1661/16 the board found that independent claim 7 lacked clarity: the last feature, added during the opposition procedure and objected to by the appellant (opponent), left it unclear to the skilled person what further structural or functional limitation to the claimed arrangement could be implied by this feature. Rejecting different arguments from the patent proprietor, the board emphasised that the clarity requirement of Art. 84 EPC for an amendment was a substantive one, and that the subjective component in the task of interpretation was eliminated by taking the position of the skilled person. Thus it could objectively be concluded that the claim as amended was not clear. For the claim as a whole to be clear, the meaning, in terms of the limiting effect, of features introduced into a claim must be clear.

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). In T 2968/19 the board made it clear that the requirement under Art. 84 EPC that the claims be concise was an independent condition designed to prevent the clear interpretability of a claim from being compromised, for instance by redundant features. However, it was not to be applied in a way that would restrict the clarity requirements under Art. 84 EPC.

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. The fact that in a lower ranking request the offending feature no longer has to be relied upon to establish a distinction over the prior art does not overcome the defect pursuant to Art. 84 EPC. Nor does it give the deciding body the discretion to disregard the deficiency. In particular, it has to be borne in mind that the significance of a feature may become apparent only at a later stage in the life of a patent, e.g. in opposition or revocation proceedings. Moreover, the board noted that a deficiency concerning the requirements of Art. 84 EPC was neither a ground for opposition before the EPO under Art. 100 EPC nor a ground for revocation under Art. 138(1) EPC. Consequently, such a deficiency cannot be dealt with, let alone remedied in either proceedings.

A prerequisite for arriving at a technically sensible claim interpretation is that the claim is technically consistent: if two features are separately clear, but inconsistent with each other from a technical point of view, then their combination, and the claimed subject-matter, cannot be clear (T 935/14). In T 765/15 the board pointed out that claims 1 and 2 contradicted each other, although claim 2 depended on claim 1. As a consequence, the claim set was unclear according to Art. 84 EPC 1973.

In T 2574/16 the examining division had found the method of claim 1 to be unclear in view of an example disclosed in the description. The board noted that the claim did encompass elaborate simulations going beyond any of the examples disclosed in the application as filed. But this in itself was not a problem of lack of clarity (or insufficiency of disclosure). In fact, it was normal for a claim to define the scope of protection in terms that positively define the essential features of the invention. Any particular embodiment falling within the scope of the claim could have further characteristics not mentioned in the claim or disclosed in the application (and could even constitute a patentable further development).