The concept of “plausibility” is not a formal ground for refusing an application or revoking a granted patent at the EPO. Instead, it has been developed through case law to assess whether a purported effect - such as treatment of a particular disease - is credible to the skilled person based on the disclosure of the application as filed and the common general knowledge in the art. Since this case law has been inconsistent, questions on the standard for assessing plausibility have recently been referred1to the EPO's Enlarged Board of Appeal.
Should plausibility be a factor in considering patentability?
Firstly, the Enlarged Board has been asked to confirm whether plausibility should even be considered when assessing patentability, given that there is no concept of “plausibility” within the rules and articles of the EPC.
EPO and national court practice in Europe seem to consistently agree that there must be some explanation of the claimed effect in the application as filed to prevent “armchair inventors” obtaining a monopoly for something they had not actually invented when the application was filed. Therefore, it seems likely that the Enlarged Board will confirm that some standard of plausibility is required.
If so, what is the correct standard for plausibility?
Assuming the Enlarged Board confirms that plausibility is necessary, it will move on to consider what standard should be applied when assessing plausibility. The EPO's Technical Boards of Appeal have applied different approaches to the assessment of plausibility, hence the need for the Enlarged Board to set out a uniform approach. The referring decision identifies two possible standards for the assessment of plausibility: “ab initio plausibility” and “ab initio implausibility”.
Ab initio plausibility applies a positive plausibility test: it must actively be plausible from the application as filed that the invention achieves the effect the patentee asserts that it does. Ab initio plausibility generally does not allow post-published evidence to be taken into consideration when assessing plausibility. By contrast, ab initio implausibility sets out a lower standard for plausibility and generally allows post-published evidence to be taken into consideration unless there is a reason to doubt the effect would have been achieved.
Both standards have been widely applied by the Technical Boards of Appeal, so it is not clear which approach the Enlarged Board might favour. The Enlarged Board of Appeal has not yet set a date for oral proceedings, but these are expected to take place in 2023. We will continue to monitor the referral and provide an update in due course.
Practical considerations
Even if the Enlarged Board ultimately favours the ab initio implausibility test, and thus sets a relatively low bar for establishing plausibility at the EPO, it is worth remembering that the national courts may have their own plausibility standards. For example, the UK Supreme Court applied the more strict ab initio plausibility test in Warner-Lambert v Generics2. Therefore, even if the Enlarged Board were to require a lower standard of plausibility, positive pointers towards an effect in the application as filed may still be necessary to successfully enforce national rights resulting from a granted European patent.
The level of evidence required for a claimed effect to be considered plausible is influenced by the facts of the case. More evidence may be necessary where the claims are broader, the technical field is younger and the technology in question is unpredictable. The EPO and national courts have acknowledged that clinical trials or animal data are not always necessary for an effect to be plausible - in many instances, in vitro data may be sufficient. Again, however, this depends on the facts of the case in question.
The referring decision can be read here3
Footnotes
1 EPO - Referrals pending before the Enlarged Board of Appeal
2 Warner-Lambert Company LLC (Appellant) v Generics (UK) Ltd t/a Mylan and another (Respondents) - The Supreme Court
3 EPO - T 0116/18 () of 11.10.2021
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