KKO:2025:107 - Burden of proof regarding the validity of the priority claim of a European patent

Background and the issue before the Supreme Court

Company A had been granted a European patent for a medicinal product, in effect in Finland, and Company A was also the holder of a supplementary protection certificate granted in Finland on the basis of the said basic patent.

The basic patent had been transferred to Company A by Company B, which had been the applicant for the basic patent. In the basic patent specification, there was a mention of a priority claim filed by Company B on the basis of a provisional application for patent that the inventors had filed in the United States. The inventors had transferred their rights to the provisional application to Company C, a wholly owned subsidiary of Company B.

Company X had brought an action before the Market Court for the invalidity of the basic patent and the supplementary protection certificate, alleging e.g. lack of novelty. This allegation arose from the claim that the priority claim mentioned in the patent specification was without effect, as the relevant right had not been validly transferred to the applicant for the basic patent. The Market Court declared the European patent and the supplementary protection certificate invalid.

The issue before the Supreme Court was the burden of proof regarding the validity of a priority right in a situation where the priority claim has been mentioned in the patent specification of the European patent, with the matter turning especially on the questions of whether, and how, the applicant for a European patent may be considered to be a legitimate claimant for the priority right.

Domestic provisions on the burden of proof and standard of evidence

Under chapter 17, section 2(1), of the Code of Judicial Procedure, in a civil matter a party shall prove the circumstances on which their claim or objection is based. Under subsection (2) of the same section, a circumstance may be taken as grounds for the judgment only on condition that a party has presented credible evidence regarding it. Under subsection (4) of the same section, the provisions in subsections (1) and (2) are to be observed unless otherwise provided by law on the burden of proof or on the required standard of evidence, or unless the nature of the matter otherwise requires.

In the preparatory works concerning subsection (4), it is noted that the main criteria for assessing the nature of the matter include prior understanding of probabilities, the availability of evidence to the parties, and the functionality of the relevant legislation. Rules on the burden of proof may be laid down also in case-law (Bill 46/2014, page 48).

Domestic provisions on declaring a patent invalid

Under section 52(1)(1) of the Patents Act, the court shall declare a patent invalid, in a relevant action, if the patent relates to an invention that does not satisfy the requirements of e.g. section 2.

Under section 2(1) of the Patents Act, patents may only be granted for inventions which are new in relation to what was known before the filing date of the patent application, and which also differ essentially therefrom.

Under section 70m(1) of the Patents Act, a European patent application which has been accorded a filing date by the European Patent Office shall have the same effect in Finland as a Finnish patent application filed on the same date. If, under the European Patent Convention, the application enjoys priority from an earlier date than the filing date, such priority shall have effect also in Finland.

Filing for a priority right under the European Patent Convention

Under Article 87(1) [1973] of the Convention on the Grant of European Patents (European Patent Convention, EPC), a person who has duly filed in or for any State party to the Paris Convention for the Protection of Industrial Property, an application for a patent or for the registration of a utility model or for a utility certificate or for an inventor’s certificate, or his successors in title, shall enjoy, for the purpose of filing a European patent application in respect of the same invention, a right of priority during a period of twelve months from the date of filing of the first application. Under paragraph (2) of the same Article, every filing that is equivalent to a regular national filing under the national law of the State where it was made or under bilateral or multilateral agreements, including this Convention, shall be recognised as giving rise to a right of priority.

Under Article 88(1) [1973] EPC, an applicant for a European patent desiring to take advantage of the priority of a previous application shall file a declaration of priority, a copy of the previous application and, if the language of the latter is not one of the official languages of the European Patent Office, a translation of it in one of such official languages.

Decision of the Enlarged Board of Appeal of the European Patent Office of 10 October 2023

In its decision of 10 October 2023 in consolidated cases G 1/22 and G 2/22, the Enlarged Board of Appeal of the European Patent Office made a change in the prior practice of the European Patent Office. The Board of Appeal held that since the creation, the existence, and the effects of the priority right are governed only by the EPC, priority rights are autonomous rights under the EPC and should be assessed only in the context of the EPC, regardless of any national laws (paras. 84–86 and 129–130). The European Patent Convention does not impose any formal requirements for the transfer of the priority right by agreement (para. 86, in conjunction with para. 68).

The Board of Appeal held also that there is a rebuttable, but strong presumption of entitlement to priority if the applicant claims priority in accordance with Article 88(1) EPC (paras. 101–107, 110, and 131). The presumption of entitlement should be rebuttable in rare and exceptional cases, where the priority applicant may have legitimate reasons not to allow the subsequent applicant to rely on the priority. Such cases could, for example, be related to bad faith behaviour on the side of the subsequent applicant (paras. 108, 110, and 131). The rebuttable presumption involves the reversal of the burden of proof, that is, the party challenging the subsequent applicant’s entitlement to priority has to prove that this entitlement is missing (para. 110).

Assessment by the Supreme Court

The Supreme Court noted that the right to claim a priority right for a European patent is governed by Article 87 EPC, and that the decision of the Enlarged Board of Appeal of the European Patent Office described above concerned the interpretation of that Article. That being said, the decision pertained to proceedings before the European Patent Office, and it was not in itself binding on national courts when dealing with a case pertaining to the validity of a priority right of a European patent (para. 115 of the decision).

This was a case pertaining to the validity of a European patent in effect in Finland, governed primarily by Finnish law. The provisions of the Code of Judicial Procedure on the burden of proof were applicable. Accordingly, the assessment was to be based on the general burden-of-proof rule in chapter 17, section 2(1), of the Code, and on the requirement of credible evidence in subsection (2) of the same section. That said, under subsection (4) of the same section, it was possible to diverge from the application of the general burden-of-proof rule e.g. if the nature of the matter so requires. Criteria for the assessment of the nature of the matter include e.g. prior understanding of probabilities, the availability of evidence to the parties, and the functionality of the relevant legislation. The Supreme Court noted that the provisions in chapter 17, section 2, of the Code of Judicial Procedure are in this respect flexible.

The Supreme Court held that considerations of the functionality of the legislation concerning European patents and of legal certainty provided firm support for interpreting the Finnish Patent Act in harmony with the European Patent Convention. The objective of harmonisation of the Convention and domestic interpretations featured also in the preparatory works of the Patent Act and the Supreme Court held that it should be observed also in the present case. The Supreme Court also noted that, in view of the prior understanding of probabilities, there was good reason to impose the burden of proof on the party that challenges a priority claim on grounds relating to the transfer of the relevant right. Moreover, it is not unreasonable to expect that the party challenging a priority claim present evidence in support of the challenge.

The Supreme Court noted that the provisions in chapter 17 of the Code of Judicial Procedure on the burden of proof allowed for the application of a burden-of-proof rule that corresponds to the rule stated in the decision of the Enlarged Board of Appeal of the European Patent Office described above. Also in several other European states, the courts had held that the burden-of-proof rule stated in that decision was applicable, as far as not precluded by national legislation.

In conclusion, the Supreme Court held that, in Finland, there was reason to apply a burden-of-proof rule that corresponds to the rule stated in the 10 October 2023 decision of the Enlarged Board of Appeal of the European Patent Office in consolidated cases G 1/22 and G 2/22. Accordingly, the applicant for a European patent is presumed to be entitled to priority, if the priority claim meets the criteria set in Article 88(1) EPC. This presumption is rebuttable only in rare and exceptional cases. The burden of proof regarding the circumstances on which the challenge is based lies on the party challenging the priority claim.

This strong presumption of entitlement to priority should have been applied in the present case. The Supreme Court vacated the judgment of the Market Court and remanded the case to the Market Court for the assessment of whether Company X had presented sufficient evidence in support of its challenge to the priority claim in question.