Added Subject-Matter in a Divisional Patent: The French Court of Cassation Clarifies the Assessment under the EPC
The French Court of Cassation provides important guidance on the assessment of added subject-matter and intermediate generalisations in European divisional patents.
On 3 December 2025, the French Court of Cassation issued an important decision concerning the prohibition against adding subject-matter to a European divisional patent under Articles 123(2) and 138(1)(c) of the European Patent Convention (EPC).
The case concerned Nintendo's European patent relating to the controller of the Wii video game console and provides valuable guidance on the assessment of intermediate generalisations and the role of the person skilled in the art when determining whether an amended claim extends beyond the content of the parent application.
Legal Framework
Article 123(2) EPC provides that a European patent application or patent may not be amended in such a way that it contains subject-matter extending beyond the content of the application as originally filed.
In addition, Article 138(1)(c) EPC provides that a European patent may be revoked if its subject-matter extends beyond the content of the application as originally filed or, in the case of a divisional application, beyond the content of the earlier (parent) application as filed.
These provisions reflect one of the fundamental principles of European patent law: applicants may not improve or broaden their inventions during prosecution by introducing technical information that was not directly and unambiguously disclosed in the original application.
Background
Nintendo Co., Ltd. owned European divisional patent EP 1 495 518, relating to technology used in the Wii video game controller.
Following a cease-and-desist letter sent to Bigben Interactive, a manufacturer of video game accessories, Bigben brought proceedings seeking revocation of the French designation of the patent.
During the examination procedure, claim 1 had been amended to include an acceleration sensor located within the controller housing.
Bigben argued that this amendment introduced subject-matter extending beyond the disclosure of the parent application.
In a judgment dated 21 April 2023, the Paris Court of Appeal agreed and declared the French part of the patent invalid, holding that the amendment constituted an inadmissible intermediate generalisation.
Nintendo appealed to the French Court of Cassation.
Issue 1: Did the Court of Appeal Correctly Interpret the Parent Application?
The first issue before the Court of Cassation was whether the Court of Appeal had correctly interpreted the disclosure of the parent application when assessing the alleged inadmissible intermediate generalisation.
The Court of Appeal held that the parent application disclosed a necessary technical relationship between the acceleration sensor (68) and the processor (66). It relied on both the description and Figure 8 of the parent application, concluding that the acceleration sensor had only been disclosed in combination with the processor. Consequently, by amending claim 1 to include the acceleration sensor without also including the processor, the patent extracted an individual technical feature from a combination of features originally disclosed together, thereby creating an inadmissible intermediate generalisation.
The Court of Cassation disagreed.
It observed that the description of the parent application expressly 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 12." The reference to "or any other processor" showed that the application did not present the acceleration sensor as being inextricably linked to processor 66.
Accordingly, the Court of Appeal had incorrectly interpreted the content of the parent application by treating the acceleration sensor and processor 66 as an inseparable combination. In doing so, it distorted the clear wording of the patent specification, contrary to the principle that courts must not misrepresent the content of written evidence.
Issue 2: The Importance of the Person Skilled in the Art
The Court of Cassation also criticised the Court of Appeal for failing properly to apply the "direct and unambiguous disclosure" test under the EPC.
The Court of Appeal had considered that there was no evidence that a processor necessarily formed part of a video game controller. It therefore concluded that the acceleration sensor could not be isolated from the combination originally disclosed in the parent application. In its view, introducing the acceleration sensor into claim 1 without also including the processor amounted to extracting a single technical feature from a disclosed combination of features, resulting in an inadmissible intermediate generalisation.
The Court of Cassation recalled that the assessment under Article 123(2) EPC must be carried out from the perspective of the person skilled in the art. The relevant question is whether the amended subject-matter derives directly and unambiguously, either explicitly or implicitly, from the earlier application as filed.
Importantly, this assessment is not limited to the express wording of the application but also includes technical information that would be implicitly and necessarily understood by the person skilled in the art.
However, the Court of Appeal had failed to identify the relevant person skilled in the art and had not examined whether such a person would necessarily understand that an acceleration sensor requires a processor capable of processing the data generated by that sensor. If so, the presence of a processor could constitute implicit technical knowledge and would not necessarily need to be expressly included in the claim.
By failing to conduct that analysis, the Court of Appeal deprived its decision of a sufficient legal basis under Articles 123(2) and 138(1)(c) EPC.
Practical Implications
Although the Court of Cassation did not decide whether the patent ultimately complied with Article 123(2) EPC, its judgment provides important guidance on the assessment of added subject-matter in European patent disputes.
First, courts must interpret the original disclosure carefully and avoid reading technical limitations into the application that are not actually present.
Second, the assessment of added subject-matter cannot be performed solely by comparing the wording of the original application and the amended claim. It must be carried out from the perspective of the person skilled in the art, taking into account both the explicit disclosure and the technical knowledge that would be implicitly understood by that person.
Finally, the judgment illustrates that allegations of inadmissible intermediate generalisation require a detailed technical and legal analysis rather than a purely literal reading of the patent specification.
Key Takeaways
This decision provides several practical lessons for patent applicants and patentees:
- amendments to patent claims must remain firmly supported by the original disclosure;
- courts should avoid construing the original application more narrowly than its actual wording permits;
- the assessment of added subject-matter must always be conducted from the perspective of the person skilled in the art, taking into account both explicit and implicit disclosure; and
- careful drafting of the original patent application remains the best protection against future validity challenges based on Article 123(2) EPC.
Elsa Duboin, Trainee Lawyer
Christine Chai, Managing Partner, Attorney-at-Law
