On March 23rd, 2023, the Enlarged Board of Appeal of the EPO issued the long-awaited decision concerning the concept of plausibility and the role of post-published data in the evaluation of the inventive step requirement.
Following the referral of the Board of Appeal of the EPO dated October 11th, 2021, the Enlarged Board of Appeal was required to answer the following questions:
“If for acknowledgement of inventive step the patent proprietor relies on a technical effect and has submitted evidence, such as experimental data, to prove such an effect, this evidence not having been public before the filing date of the patent in suit and having been filed after that date (post-published evidence):
- Should an exception to the principle of free evaluation of evidence (see e.g. G 3/97, Reasons 5, and G 1/12, Reasons 31) be accepted in that post-published evidence must be disregarded on the ground that the proof of the effect rests exclusively on the post-published evidence?
- If the answer is yes (the post-published evidence must be disregarded if the proof of the effect rests exclusively on this evidence), can the post-published evidence be taken into consideration if, based on the information in the patent application in suit or the common general knowledge, the skilled person at the filing date of the patent application in suit would have considered the effect plausible (ab initio plausibility)?
- If the answer to the first question is yes (the post-published evidence must be disregarded if the proof of the effect rests exclusively on this evidence), can the post-published evidence be taken into consideration if, based on the information in the patent application in suit or the common general knowledge, the skilled person at the filing date of the patent application in suit would have seen no reason to consider the effect implausible (ab initio implausibility)?”
The questions referred to the Enlarged Board of Appeal are of particular importance when it comes to the evaluation of the validity of patents in the chemical, pharmaceutical or biotechnological industries, where the need to obtain timely patent protection is difficult to reconcile with the length of the experiments.
In a first-to-file system, it may indeed happen that applicants file a patent application before having experimental data supporting that the technical problem is effectively solved by the claimed invention. Moreover, filing the patent application could represent itself a way to attract funds for expensive trials, which may not take place in absence of significant investments.
Nevertheless, the difficulties that might be faced while assessing how early in the research and development process a patent application should be filed must be balanced with the necessity to prevent speculative patents, i.e. patents whose technical contribution is based solely on assertion and there is no reason to suppose that the latter is true. The relevant question, then, is where to draw the line between speculation and a patentable invention.
In order to address such issues, the EPO first elaborated the concept of plausibility of the invention, which can be summarized as the burden to demonstrate the existence of reasonable elements, at the time when the patent application is filed, for supposing that a solution to the technical problem has really been found and disclosed. The concept has been later embraced also by national courts, especially in UK, and became a threshold common to inventive step and sufficiency of disclosure.
However, the lack of a clear legal basis has been creating many divergences among scholars and courts, both on how strictly the requirement should be interpreted and which shall be the role of post-published data. The uncertainties thus led the EPO to refer the mentioned questions to the Enlarged Board of Appeal.
By its decision, which partly redraws the boundaries of the referred questions, the Enlarged Board of Appeal actually moved away from the conceptional notions established over time, defining plausibility as a “generic catchword” (see par. 58 and 92).
First, the ruling clarified that post-published data cannot be disregarded solely on the ground that such evidence, on which the effect rests, had not been public before the filing date of the patent and was filed after that date, since the principle of the free evaluation of evidence must prevail (par. 55 and 56).
Nevertheless, according to the Board, "the core issue rests with the question of what the skilled person, with the common general knowledge in mind, understands at the filing date from the application as originally filed as the technical teaching of the claimed invention" (par. 71 and 93). Therefore, "a patent applicant or proprietor may rely upon a technical effect for inventive step if the skilled person, having the common general knowledge in mind, and based on the application as originally filed, would consider said effect as being encompassed by the technical teaching and embodied by the same originally disclosed invention" (par. 94).
Overall, it appears that the Enlarged Board of Appeal is of the opinion that the ab initio plausibility and ab initio implausibility criteria can coexist. This seems to be confirmed by the fact that, after reviewing the main case-law and laying down the above principle, the Board observed that "applying this understanding to the aforementioned decisions […], the outcome in each particular case would not have been different from the actual finding of the respective board of appeal” (par. 72).
The decision probably does not meet the expectations of many and several questions survive. After all, it is the Enlarged Board of Appeal itself that recognized “the abstractness of some of the aforementioned criteria” (par. 95).
Nevertheless, although the referred questions focused on the evaluation of inventive step, the Enlarged Board of Appeal expressed few considerations also regarding the role of the post-published data in the context of sufficiency of disclosure, acknowledging its relevance when it comes to inventions for which the technical effect is expressly claimed, as for second medical use patents.
According to the judges, "the scope of reliance on post-published evidence is much narrower under sufficiency of disclosure (Article 83 EPC) compared to the situation under inventive step (Article 56 EPC). In order to meet the requirement that the disclosure of the invention be sufficiently clear and complete for it to be carried out by the person skilled in the art, the proof of a claimed therapeutic effect has to be provided in the application as filed, in particular if, in the absence of experimental data in the application as filed, it would not be credible to the skilled person that the therapeutic effect is achieved. A lack in this respect cannot be remedied by post-published evidence" (par. 77).
The above interpretation looks very much like the ab initio plausibility theory and does not help mitigating the uncertainties that applicants face when assessing how far in the research and development process to file a patent application.
In conclusion, the ruling has probably provided less clarity than expected with regard to the role of post-published data in the evaluation of inventive step, but endorsed a rather strict interpretation of the plausibility (or credibility?) test in relation to sufficiency of disclosure.
In any case, the plausibility, its boundaries and implications are very much likely to remain among the most debated topics in patent law, and they will probably be soon addressed also by the Unified Patent Court.
 G2_21_Decision_ of_the_Enlarged_Board_of_Appeal_of_23_March_2023_EN.pdf (epo.org).
 EPO - Referral to the Enlarged Board of Appeal - G 2/21.
 See for example EPO Technical Board of Appeal, September 12th, 1995, T 0939/92, Triazoles/AgrEvo, available online at EPO - T 0939/92 (Triazoles) of 12.9.1995; EPO Technical Board of Appeal, June 28th, 2005, T 1329/2004, Factor-9/Johns Hopkins, available online at EPO - T 1329/04 (Factor-9/JOHN HOPKINS) of 28.6.2005).
 See, among others, Warner-Lambert Company LLC v Generics (UK) Ltd t/a Mylan and another,  UKSC 56, available online at https://www.supremecourt.uk/cases/docs/uksc-2016-0197-judgment.pdf.