What it is about
In decision G 1/24 of 18 June 2025 (“Heated Aerosol”), the Enlarged Board of Appeal of the European Patent Office (EPO) settled a question that had been disputed for years: patent claims must always be interpreted in the light of the description and the drawings – not only where the wording of the claim is unclear or ambiguous, but as a matter of principle. The previously inconsistent case law of the Boards of Appeal, part of which consulted the description only in cases of ambiguity, has thus come to an end.
What matters in practice: this principle of interpretation expressly applies to the assessment of novelty and inventive step, and therefore directly in opposition proceedings. An interpretation of the claims that is detached from the description and drawings is no longer permissible for the assessment of patentability. The EPO thereby aligns its practice with that of the Unified Patent Court (UPC) and the national courts, which apply Article 69 EPC in this direction in any event.
For opponents and patent proprietors alike, this shifts the rules of the game. Anyone attacking or defending in opposition must now systematically take the description into account in their arguments.
Why G 1/24 is particularly relevant to opposition
At its core, opposition turns on whether the granted claim can be maintained over the prior art. Until now, it was open to debate whether a term defined or narrowed in the description had to be taken into account at all when assessing novelty and inventive step. After G 1/24, that door is closed: the description must be consulted. This makes it – to the benefit of both sides – an active instrument of interpretation.
This cuts both ways. For the opponent, new angles arise for “loading up” the claim via the description and thereby pulling it under the prior art. For the proprietor, there is a corresponding opportunity to steer the claim into a patentable range through the description – but also a new risk where description and claim do not match.
New lines of attack for the opponent
1. The description as a lever for broad interpretation. Where the description contains definitions, examples or wording that frame a claim term more broadly than the wording alone would suggest, the opponent can insist on that broad reading – with the aim that the claim, so interpreted, encompasses a prior-art document and therefore loses novelty or inventive step. The proprietor’s own definitions in the description can in this way be turned against them.
2. Exploiting inconsistencies between claim and description. Where the description departs from the claim or contains contradictory statements, this can be used to construct an interpretative latitude that works against the proprietor. Older patents in particular, granted without an eye to G 1/24, often present openings here.
3. Attacking the “technical effect” via the description. Where the proprietor bases inventive step on a technical effect, the opponent can argue that, on the broadest reasonable interpretation of the claim wording, this effect is not in fact achieved across the entire claimed scope – i.e. that the description does not support the asserted effect consistently throughout.
4. “Clarity attacks” through the back door. Although lack of clarity (Article 84 EPC) is not a ground of opposition for granted patents, a practically similar effect can be achieved through the interpretation debate: by showing that claim and description diverge, the opponent forces the Opposition Division into an interpretation that may turn out to be disadvantageous for the proprietor.
How the proprietor defends
1. Use the description actively for a narrower, patentable interpretation. G 1/24 works in both directions. The proprietor can point to definitions and embodiments in the description in order to contour a claim term such that the prior-art document is precisely not caught. The precondition is that the description actually supports this narrower reading.
2. Know the limits of G 1/24 – which only partly favour the proprietor. This is the most important point. The first follow-up decisions of the Boards of Appeal (including T 1561/23, T 1999/23, T 0161/24 and T 1465/23) have made clear that the description cannot override a clear and generally understood meaning of a term. G 1/24 does not give the proprietor the right to escape an objection based on the prior art by artificially interpreting the claims more narrowly than their ordinary meaning permits. “Consulting the description” does not mean reading limiting definitions from the description into the claim where the term already has a clearly understandable meaning. Anyone relying on this strategy alone will come up empty-handed.
3. Draft auxiliary requests carefully and consistently. Where interpretation via the description does not carry, claim limitation remains the more reliable instrument. Auxiliary requests should map the embodiment worth protecting precisely – and the description must fit. Note: the still-pending referral G 1/25 concerns precisely the question of whether and how the description must be adapted to amended claims. Until that decision, description amendments should be handled with particular care, as they may affect later interpretation before the infringement courts.
4. Defuse contradictions before the opponent finds them. In the reply, it is advisable to address problematic passages of the description early and to set out a coherent line of interpretation, rather than leaving the opponent in control of the meaning.
Strategy at a glance
For the opponent: Systematically search the description for broad definitions, examples and contradictions that pull the claim into the prior art. Challenge the asserted technical effect across the full scope of the claim. But anchor the attack where the claim wording itself leaves room – against a clear, ordinary meaning of the words, even the description cannot prevail.
For the proprietor: Use the description as a supporting instrument of interpretation, without relying on an artificially narrow reading. Where interpretation is not enough, prepare consistent auxiliary requests early. Review existing portfolios proactively for claim/description consistency – ideally before an opposition looms.
Conclusion
G 1/24 makes the description the central battleground of opposition proceedings. It is both weapon and shield: the opponent gains a new lever via broad or contradictory passages of the description, while the proprietor gains an instrument of interpretation for the defence. The boundary is drawn by the claim wording itself – a clearly understandable meaning can be neither inflated nor defined away by the description. In practice, what will decide cases more than ever is how carefully claim and description are aligned with one another. This applies to pending oppositions just as it does to the drafting of new applications.
