On 3 December 2025, the French Court of Cassation issued an important ruling concerning the prohibition of added subject-matter in the context of a European divisional patent relating to a Wii video game console controller. The decision provides valuable guidance on: the assessment of inadmissible intermediate generalisations; the interpretation of patent documents by national courts; and the role of the “person skilled in the art” in the added subject-matter analysis under the EPC. Legal Framework Article 123(2) EPC prohibits amendments that extend the subject-matter of a European patent beyond the content of the application as originally filed. Under Article 138(1)(c) EPC, a European patent may be declared invalid if: its subject-matter extends beyond the content of the application as filed; or where granted on the basis of a divisional application, it extends beyond the content of the earlier (parent) application. The applicable test is whether the amended subject-matter derives directly and unambiguously , using common general knowledge, from the earlier application as filed. Background of the Case Nintendo Co. Ltd., proprietor of European divisional patent EP 518 relating to the Wii console controller, initiated enforcement actions against Bigben Interactive, a company marketing video game accessories. In response, Bigben brought revocation proceedings before the French courts against the French part of EP 518. During prosecution before the EPO, the patent claims had been amended to include the presence of an acceleration sensor located inside the controller housing. The Paris Court of Appeal (21 April 2023) invalidated the French part of the patent, holding that: the addition of the acceleration sensor resulted in an inadmissible intermediate generalisation, and the subject-matter extended beyond the content of the earlier application. Nintendo appealed to the Court of Cassation. The Court of Cassation’s Ruling The Court examined two central issues. 1. Distortion of the Patent Document The Court of Appeal had considered that Figure 8 and the description established a “necessary link” between: the acceleration sensor (68), and the processor (66). It concluded that isolating the acceleration sensor without expressly including a processor amounted to extracting a feature disclosed only in combination. However, the Court of Cassation held that this interpretation distorted the patent document. The parent application stated that: “ the acceleration sensor 68 can be used in combination with the processor 66 (or any other processor) to determine the inclination, altitude or position of the housing .” The wording did not establish an inextricable link between the acceleration sensor and a specific processor. By reading such a mandatory connection into the text, the Court of Appeal misrepresented the content of the earlier application and violated the principle prohibiting courts from distorting written evidence. This constitutes a significant reminder that national courts must apply a faithful and technically accurate reading of patent documents. 2. Failure to Define the “Person Skilled in the Art” The Court of Appeal further held that: there was no evidence that a video game controller necessarily included a processor; therefore, the addition of the acceleration sensor without explicitly including a processor constituted an inadmissible intermediate generalisation. The Court of Cassation rejected this reasoning. It recalled that the added subject-matter test requires assessing whether the amended feature derives directly and unambiguously from the earlier application from the perspective of the person skilled in the art, taking into account implicit technical knowledge. Crucially, the Court of Appeal failed to define the relevant skilled person and to examine whether, for such a person, an acceleration sensor would implicitly require data processing by a processor. If, from a technical standpoint, a processor is inherently necessary to process acceleration data, its presence may be implicit and need not be explicitly restated in the claim. By omitting this analysis, the Court of Appeal deprived its decision of a legal basis under Articles 123(2) and 138(1)(c) EPC. Practical Implications This decision is noteworthy for several reasons: 1. Reinforcement of the “Direct and Unambiguous” Test The ruling aligns French case law more closely with established EPO jurisprudence on added subject-matter. 2. Central Role of the Skilled Person Courts must explicitly define the relevant skilled person and assess implicit technical features through that lens. 3. Limits of the Intermediate Generalisation Doctrine Not every extraction of a feature from a disclosed embodiment amounts to an inadmissible intermediate generalisation. The decisive question is whether the feature is structurally and functionally linked to other elements in a manner that is technically inextricable. 4. Drafting and Prosecution Strategy for Divisional Applications For patent applicants, the decision highlights the importance of: drafting fallback positions with clear technical independence of features; explicitly addressing whether components are structurally mandatory or functionally optional; anticipating potential added subject-matter challenges in national revocation actions. Conclusion The Court of Cassation’s ruling provides welcome clarification on the added subject-matter analysis in the context of divisional patents. By emphasising both the prohibition of document distortion and the necessity of properly defining the person skilled in the art, the Court reinforces a technically grounded and EPC-consistent approach to invalidity assessments. The decision will likely influence future French revocation proceedings involving intermediate generalisations and divisional patents. Elsa Duboin, Trainee Lawyer Christine Chai, Managing Partner, Attorney-at-Law

Aurilex is pleased to announce that its Managing Partner, Christine Chai, has been recognised in the WTR 1000 – France 2026. The WTR 1000 is a leading international guide dedicated to identifying the world’s foremost trademark professionals, based on extensive research, peer reviews and client feedback. This recognition reflects our expertise in trademark law and broader intellectual property matters, as well as the trust placed in Aurilex by its clients. It also highlights the collective work and high standards of the Aurilex team in assisting brands with trademark protection, portfolio management and IP strategy in complex international and cross-border contexts, particularly across Europe. Aurilex regularly advises international clients on the development, protection and enforcement of their IP rights, combining legal precision with a strong understanding of multi-jurisdictional and strategic considerations.