a) General principles 

In a number of decisions, such as T 23/86 (OJ 1987, 316), T 16/87 (OJ 1992, 212), T 327/87, T 89/89, T 121/89, T 430/89, T 476/89, T 544/89, T 565/89, T 952/90, T 439/92, T 458/96, T 717/98, T 1321/04, T 1433/05, T 2145/13 and T 2651/22, the boards of appeal have laid down and applied the principle whereby the description and drawings are used to interpret the claims and identify their subject-matter, in particular in order to judge whether it is novel and not obvious. Likewise, in a large number of decisions (e.g. T 238/88, OJ 1992, 709; T 416/88; T 194/89; T 264/89; T 472/89; T 456/91; T 606/91; T 860/93; T 287/97; T 250/00; T 505/04), the boards interpreted the claims in the light of the description and drawings in order to establish whether they were clear and concise within the meaning of Art. 84 EPC 1973.

In other decisions, however, the limits to interpretation in the light of the description and drawings are emphasised (see in this chapter II.A.6.2.2a) and II.A.6.2.3d)). A discrepancy between the claims and the description is not a valid reason to ignore the clear linguistic structure of a claim and to interpret it differently (T 431/03) or to give a different meaning to a claim feature which in itself imparts a clear credible technical teaching to the skilled reader (T 1018/02, T 1395/07, T 711/14, T 1456/14, T 2769/17, T 169/20, T 821/20, T 42/22, T 447/22). In T 1023/02, though, "unfortunate" claim language ("transcription" instead of "translation") in contradiction with the description of the invention was interpreted differently.

In T 197/10 the board explained that if the claims are worded so clearly and unambiguously as to be understood without difficulty by the person skilled in the art, there is no need to use the description to interpret the claims. In the event of a discrepancy between the claims and the description, the unambiguous claim wording must be interpreted as it would be understood by the person skilled in the art without the help of the description. Thus, in the event of a discrepancy between clearly defined claims and the description, those elements of the description not reflected in the claims are not, as a rule, to be taken into account for the examination of novelty and inventive step. See, similarly, T 1514/14 concerning the examination of sufficiency of disclosure.

In T 2221/10 the board referred to established case law according to which the description can be used as the patent's "dictionary" to assess the correct meaning of ambiguous terms used in claims (see in this chapter II.A.6.2.3c)). The board, however, also referred to T 197/10, pointing out the limits to the interpretation in the light of the description and drawings. See also T 2328/15 and T 1642/17.

In T 1924/20 the board stated that a skilled reader of a patent claim would, for many reasons, interpret the claims based essentially on their own merits (see e.g. T 2764/19 and T 1127/16). This was because the "subject-matter of the European patent" is defined by the claims and only by them. The board explained that the description and drawings were, however, typically used by the deciding body to determine the above-mentioned "skilled reader" and, hence, the viewpoint from which the claims are interpreted. This meant that, when interpreting the claims, the description and drawings could not be relied on as a sort of fall-back or supplementary-guidance tool for filling up gaps or for resolving inconsistencies in a claim to the patent proprietor's advantage. Such a reliance on the description and the drawings by the patent proprietor would normally fail to convince.

According to the board in T 177/22, a given patent claim's subject-matter must be interpreted and determined in a uniform and consistent manner (see T 1473/19). This excludes interpreting the same claim differently when assessing sufficiency of disclosure on the one hand, and when assessing novelty and inventive step on the other hand. It also presupposes that the same principles of claim interpretation must be applied when assessing compliance with any of these requirements under the EPC.

In T 439/22 of 24 June 2024 (OJ 2024, A104) the board concluded that the case law of the boards was divergent on the following questions: a) legal basis for construing patent claims; b) whether it is a prerequisite for taking the figures and description into account when construing a patent claim, that the claim wording, when read in isolation, be found to be unclear or ambiguous; and c) the extent to which a patent can serve as its own dictionary. To ensure the uniform application of the law, the board referred questions to the Enlarged Board. Decision G 1/24 (OJ 2025, A60) is summarised above in chapter II.A.6.2.1.

In T 409/97 the board held that an erroneous statement in the introduction to the description, according to which a process according to the general part of claim 1 was known from a prior art document D1, was of no assistance in interpreting the claim and establishing the subject-matter for which protection was being sought, where this statement contradicted the actual content of D1.