6.1. General principles

According to the established case law, the skilled person should try, with synthetical propensity, i.e. building up rather than tearing down, to arrive at an interpretation of the claim which is technically sensible and takes into account the whole disclosure of the patent. The patent must be construed by a mind willing to understand, not a mind desirous of misunderstanding (see inter alia T 190/99, T 920/00, T 500/01, T 1023/02, T 749/03, T 405/06, T 2480/11, T 2456/12, T 383/14, T 1477/15, T 448/16, T 111/22).

As stated in T 10/22, when it comes to claim construction the often-used reference to "a mind willing to understand" is about relying on "a mind willing to objectively construe a claim", rather than "a mind willing to understand the applicant's or patent proprietor's alleged intention". This is mainly so because it would be to the detriment of third parties and the public if claim construction depended on the alleged intention of the applicant or proprietor.

A considerable number of decisions have held that the skilled person, when considering a claim, should rule out interpretations which are illogical or which do not make technical sense (see inter alia T 190/99, T 552/00, T 920/00, T 1023/02, T 749/03, T 859/03, T 1537/05, T 1204/06, T 383/14, T 681/15). Some decisions (T 1408/04, T 1582/08, T 493/09, T 5/14) have emphasised that this is understood to mean only that technically illogical interpretations should be excluded. A mind willing to understand does not require that a broad term need be interpreted more narrowly (even if, as in the case underlying T 1408/04, the narrower interpretation would refer to a structure which is very common, but not exclusive, in the technical field concerned). In T 1514/14 the board noted that when a claim requires interpretation, the skilled person will endeavour to interpret it in a technically sensible manner and in the overall context. However, this of course did not mean that only those interpretations which fulfil the requirements of the EPC can be considered technically sensible. See also T 566/20.

In T 837/24 the board held that a claim construction omitting a technically meaningful feature did not constitute a good-faith interpretation of the claim. When construing a claim, the skilled reader typically makes use of a "mind willing to understand". Therefore, each claim feature is typically given a technical meaning when construing the subject-matter of a claim in an objective manner (T 423/23, T 10/22).

It is a well-established principle laid down in the boards' case law that a non-specific definition in a claim should be given its broadest technically sensible meaning in the context of that claim (see e.g. T 79/96, T 596/96, T 1266/19). T 1553/19 applied this rule of claim construction to a feature defined in a negative manner ("in absence of […] metal organic catalyst"). The board explained that the broadest scope of the claim corresponded to the narrowest (i.e. most limited) technically sensible definition of the element to be excluded.

In T 2047/23 the board stated that the deciding body's duty was to assess a claim against all interpretations that were technically sensible to the skilled reader. The board was aware that other decisions, such as T 367/20, had suggested that a deciding body must choose a single "correct" interpretation where mutually exclusive interpretations exist. However, it found that the decisive criterion in this regard was what the reader skilled in the respective technical field would understand from the technical terms of a claim. As explained in T 405/24, an approach that forces a choice for a single "correct" interpretation, such as the one derivable from the description, would jeopardise legal certainty. Such an approach could lead to the untenable result that some provisions of the EPC, such as Art. 123(2) EPC, might be rendered ineffective.

In T 1354/18 the board pointed out that patent claims convey a technical teaching and are directed to a reader with technical knowledge in the field of the application. The correct interpretation of claim features must therefore always be based on their technical literal meaning in the overall technical context of all features from the perspective of a person skilled in the art and not on a purely linguistic analysis of the wording of individual terms. The terms used in patent documents should therefore primarily be given the meaning they usually conveyed in the relevant state of the art. This could easily lead to a situation where the skilled person in the relevant technical field understands certain terms differently on the basis of their general technical knowledge than on the basis of a purely linguistic analysis. Moreover, the patent specification itself could attribute a specific meaning to individual features that deviated from a purely linguistic understanding; in this respect, a patent document could be its own dictionary. The interpretation must lead to a technically sensible result, whereby the claims should normally be attributed the broadest technically sensible meaning. The linguistic analysis of a feature could at best complement or confirm the analysis of the technical meaning, but could not replace it. See also T 2007/19 and T 2078/17. In T 1382/20, the board remarked that even though claims are addressed to a person skilled in the art rather than a linguist, the applicable grammar rules also had to be considered when determining the technical subject-matter of a claim – which is always expressed in linguistic terms – from the skilled person's perspective.

According to the Enlarged Board in R 25/22, claim interpretation, being a question of law, falls within the exclusive competence of the competent board. A board may adopt the interpretation proposed by one or more parties but is in no way bound by the parties’ submissions in this regard (see also R 14/23, T 1973/23, T 837/24).

As noted by the board in T 1513/12, an interpretation of a claim agreed by the parties to the proceedings was not to be regarded as binding on the board: the "principle of party disposition" was not to be understood as meaning that the parties to the proceedings could choose an interpretation of the patent which, although it might be satisfactory for them, might have implications for others not party to the proceedings. Confirmed in T 2319/18 and T 1024/19. Likewise, in T 583/23 the board’s interpretation deviated from the interpretation adopted by both parties.

In T 1473/19 the board pointed out that claim interpretation is overall a question of law which must ultimately be answered by the deciding body, and not by linguistic or technical experts. It does, however, involve the appraisal of linguistic and technical facts which may be supported by evidence submitted by the parties. In T 450/20 and T 1494/21 the board concurred with this statement and it stressed that a board of appeal is not limited to the claim interpretations advanced by the parties but may also adopt a claim interpretation of its own. Relying on documentary evidence is not a precondition for the adoption of a certain claim interpretation by a board of appeal. In this context evidence can only be relied upon to prove facts, such as how the person skilled in the art understood a certain technical term in a certain prior art document at a certain point in time, but not to ultimately ascertain whether a certain claim interpretation is correct or not.

In T 1193/23, the respondent had based its discussion of various terms used in the claim on answers received from the chatbot ChatGPT. The board held ChatGPT's answer to be irrelevant per se since the interpretation of the claim depended on how it was understood by the skilled person (see also T 206/22). According to the board, the mere fact that chatbots based on large language models and/or artificial intelligence are becoming ever more prevalent, this alone does not imply that an answer received – which is derived from training data unknown to the user and also dependent on the context and the exact wording of the query/queries – necessarily accurately reflects the understanding of the skilled person in the relevant technical field at the relevant time. Proof of how the skilled person interprets particular terms in the claim of a patent (or patent application) could be furnished by appropriate technical literature, for example.

In several decisions, the boards took the view that there exists no file wrapper estoppel in proceedings under the EPC (see T 1837/06 and T 1042/15). In T 325/23 the board agreed that in general there exists no file wrapper estoppel in proceedings under the EPC. However, the interpretation argued by the appellant (patent proprietor) during the prosecution of the patent application could be taken as an indication that said interpretation was at least not technically unreasonable. Such an interpretation did not correspond to a "file wrapper estoppel" because it did not limit the interpretation of a certain feature to what was argued by the then applicant for all future proceedings. Rather, the consideration of such events in the file history was used to determine whether an interpretation was technically reasonable or not, without excluding other interpretations.

For interpretation in the context of the claim as a whole see e.g. T 1886/22 and T 1345/23; see however also T 42/22 in which the board found that the independent product and method claims should be interpreted independently.

The Enlarged Board ruled in G 1/24 (OJ 2025, A60) that the claims are the starting point and the basis for assessing the patentability of an invention under Art. 52 to 57 EPC. The description and drawings shall always be consulted to interpret the claims when assessing the patentability of an invention under Art. 52 to 57 EPC, and not only if the person skilled in the art finds a claim to be unclear or ambiguous when read in isolation. The consultation of the description and drawings to interpret the claims is dealt with extensively in the following section II.A.6.2.