Insufficiency resulting from mutually exclusive definitions: The repercussive effect of dependent claims (T 0878/23)

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Nov 10, 2025, 4:35:59 AM (11 days ago) Nov 10

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Insufficiency resulting from mutually exclusive definitions: The repercussive effect of dependent claims (T 0878/23)

Dr Rose Hughes Friday, November 07, 2025 - claim intepretation, epo, G1/24, patents, PatKat, Rose Hughes, sufficiency

Since G1/24, we have become used to the debate of how much the definitions in the description may influence the claims. The recent Board of Appeal decision in T 0878/23 highlights how contradictions in the claims themselves may be enough to invalidate a patent for insufficiency. The case involved a Nestlé patent on probiotics, where the claims contained mutually exclusive definitions of amino acid concentrations. While the Patentee argued this was a simple clarity issue, and thus off-limits during opposition, the Board of Appeal saw it differently. The Board of Appeal found the contradictory claim language made it "technically impossible" for the skilled person to work the invention over the whole range, leading to a fatal finding of insufficiency.

Legal Background: Sufficiency (Article 83 EPC) vs. clarity (Article 84 EPC)

Article 83 EPC requires that the European patent application "discloses the invention in a manner sufficiently clear and complete for it to be carried out by the person skilled in the art." According to the established case law, the disclosure must allow the invention to be performed over substantially the whole range claimed. An objection of insufficiency requires there to be serious doubts, substantiated by verifiable facts, that the skilled person would be able to work the invention over the whole of the claimed range (IPKat). However, in many cases, the sufficiency bar is low and can be satisfied by providing a single example falling in the scope of the claim in the application as filed.

Probiotic maths

Given the wording of Article 83 EPC (i.e. "sufficiently clear"), there can sometimes be some confusion between the sufficiency and clarity requirements for patentability. However, the requirement for clarity is a distinct provision provided by Article 84 EPC, which states that "the claims shall define the matter for which protection is sought. They shall be clear and concise and be supported by the description". Distinguishing between an issue of insufficiency and a lack of clarity can be critical, given that clarity is not a ground of opposition absent newly arising clarity issues from post-grant amendments.

Case Background: T 0878/23 and the contradictory probiotic patent

The patent (EP 3317395 B1) in this case, owned by Nestlé, was directed to a common challenge in the probiotic industry, that of ensuring the viability of microorganisms. When beneficial culture powders are incorporated into products, they are required to remain viable throughout a long shelf-life. However, the beneficial bugs included in probiotics can be sensitive to a variety of stresses inherent in manufacturing and storage. The patent purported to identify a specific combination of ingredients with optimized activity to protect microorganisms in probiotics, with the granted claims relating to compositions comprising a carrier, an antioxidant, and specific combinations of amino acids.

The patent was opposed by the Japanese milk company Morinaga Milk and DSM. After the Opposition Division maintained the patent on an auxiliary request, both the Patentee and Morinaga Milk appealed the decision. The main issue on appeal was sufficiency of disclosure under Article 100(b) EPC of the claims as granted.

Mutually exclusive claim definitions

Claim 1 as granted defined minimum amounts for the amino acids: 8 to 20 wt.% for amino acids lysine, alanine, and arginine, and 2 to 10 wt.% for the amino acid cysteine. The Board of Appeal calculated that any composition falling under claim 1 must have a minimum total amino acid concentration of 10 wt%, or as much as 16 wt%, depending on the specific combination. So far, so good. The problem with the claims was the wording of dependent claim 4. This claim, depending on claim 1, defined the total amino acid concentration as being "in the range from 3.5 to 36.5 wt%". The question became, how a composition could have a total amino acid content of 3.5 wt% (as allowed by claim 4) when the claim it depends on (claim 1) required it to have at least 10 wt%? The Board of Appeal noted that "the compositions specified in claim 4 that are explicitly excluded from the concentration ranges specified in claim 1 represent[ed] a significant proportion of the range claimed" (r. 7.5).

Legal principles: The repercussive effect of dependent claims

The issue with the claims identified by the Board of Appeal resulted from the repercussive effect of dependent claim 4 on claim 1. This is in line with several decisions from the Boards of Appeal finding that dependent claims influence the interpretation of the claim from which they depend, and the general principle that dependent claims relate to sub-embodiments of the invention as defined in the claims from which they depend (G 3/14). In T 0621/20, for example, a dependent claim (claim 10) was limited to an ex vivo version of a method specified in the claim from which it depended (claim 6). The Board of Appeal concluded that the impact of claim 10 was that claim 6 must cover both performing the method in vivo and ex vivo (T 0621/20, r. 2.1.3).

The Board's decision: Why contradiction can lead to insufficiency

In the present case, the Patentee argued that the issue with dependent claims was merely a clarity issue and thus not a permissible ground for opposition (IPKat). The Patentee particularly argued that the clarity issue was one of an unclear "forbidden area', that typically arises not from a technical impossibility to perform the invention, but from an ambiguity in the claim language, such as an unclear parameter. The ambiguity in the claim makes it uncertain for the skilled person to determine whether they are working within the boundaries of the claimed invention or not. The established consensus is that such ambiguity relates to the requirements of clarity under Article 84 EPC, rather than sufficiency of disclosure under Article 83 EPC.

However, the Board of Appeal disagreed with the Patentee's analysis of the problem as a clarity issue. The Board of Appeal was not convinced that the effect of the dependent claim was just an unclear boundary. Instead, the Board of Appeal felt that the independent and dependent claims were perfectly clear, the problem was that they were also "mutually exclusive, i.e. incompatible, over a substantial part of their ranges" (r.7.6). In view of this contradiction, the Board of Appeal found that "the skilled person cannot technically prepare the composition as defined in [the dependent claim] across substantially the whole breadth claimed" (r. 7.6). In particular, the entire range from 3.5 wt% to <10 wt% was technically impossible to prepare whilst also satisfying claim 1 (r. 8.2).

All of the auxiliary requests allowed into proceedings included the same problematic dependent claim. The Board of Appeal therefore revoked the patent and rejected all of the auxiliary requests allowed into proceedings for insufficiency.

T 0878/23 is thus a reminder that, to understand the scope of a patent, it may be necessary to look at more than just the independent claims. The potential repercussive effect of dependent claims means that the meaning of an independent claim may not be as straightforward as it first appears. This is not just a European issue, but can also affect US patents (see for example, Littelfuse v. Mersen, Fed. Cir. 2022, IPWatchDog).

Final thoughts

As T 0878/23 reminds us, context is always important for claim interpretation. An individual patent claim cannot be read in isolation. The other claims in the list may influence its interpretation. To further complicate things, the principle of the repercussive effect of dependent claims is also subject to the requirement of considering the disclosure of the patent as a whole and how a skilled person would understand the invention (see for example, T 1603/13, r. 2.6 and T 1023/02, r. 9).

A notable aspect of the Board of Appeal's reasoning in T 0878/23 was that neither the interpretation of an independent or dependent claim was considered to take precedence, absent other contextual information. As such, if the invention does not make sense given the wording of a dependent claim, the patentee runs the risk of an insufficiency attack.

Following G1/24, there is still considerable debate over whether and how much the description may influence the interpretation of clear claim language. Part of this debate has focused on the consequences of contradictions between the claims and the description (IPKat). Part of the justification of mandatory adaptation of the description to the claims (the subject of its own referral in G1/25), has been the need to prevent a lack of clarity resulting from differences between the invention as defined by the description and the claims. According to the Board of Appeal's view in T 0878/23, contradictory and mutually exclusive definitions can also lead to insufficiency issues.