Plausibility demystified - a review of EPO case law before G 2/21

The European patent attorney community is currently eagerly awaiting the decision of the Enlarged Board of Appeal referral G 2/21 on the thorny topic of plausibility and post-filed evidence. 

In its preliminary opinion for G 2/21, the Enlarged Board of Appeal (EBA) raised some eyebrows by appearing to reference the standard test for sufficiency (IPKat). The sufficiency test is considered a relatively low bar, whereby an invention is considered sufficiently disclosed in view of the lack of any substantiated doubts that a skilled person could work the invention. Establishing the plausibility of an invention is often considered a higher bar than the standard sufficiency test.  However, in this Kat's view, the EBA preliminary opinion is aligned with the EPO's normal use of the term plausibility, according to which plausibility is not a higher sufficiency bar. While we wait for G 2/21, it is therefore worth stepping-back and taking a broader look at plausibility and its use in the established case law of the Boards of Appeal. 

The problem of plausibility

There are two reasons why the concept of plausibility can appear so muddled (or in Sir Robin Jacob's words, "Humpty-Dumpty-ish"). First, plausibility is not a legal concept finding explicit basis in the EPC. The EPC requires an invention to be sufficiently disclosed (Article 83 EPC), but does not mention "plausibility". Second, plausibility is employed by the EPO in a number of different contexts, including the sufficiency of medical use inventions and inventions involving broad ranges, as well as in inventive step analysis. 

However, once the rationale behind the plausibility test is understood, in this Kat's view, it becomes clear that there is nothing mysterious or difficult about the concept. Plausibility is simply the way in which the EPO expresses a higher degree of existing doubt about certain types of invention. If there is more underlying doubt that an invention will work, then an applicant must provide more evidence and information about the invention in exchange for the grant of a patent. The need for this additional evidence is the plausibility requirement. 

Basic Sufficiency

In order to understand plausibility, it is first necessary to understand sufficiency. In order to be sufficiently disclosed under Article 83 EPC, a detailed description of at least one way of carrying out the invention must be given in the application. An objection of insufficiency requires there to be serious doubts, substantiated by verifiable facts, that the skilled person would be able to work the invention (II-C, 9). As the recent case T 0500/20 confirmed, the sufficiency bar is usually low, and can be satisfied by providing a single example falling in the scope of the claim in the application as filed. 

Therapeutic use plausibility (Fish medicine, T 1571/19)

Grasping the slippery concept of plausibility

For most inventions there usually are not any serious doubts, substantiated by verifiable facts, that the skilled person would be able to work the invention. For other types of invention, however, there is greater doubt about whether a skilled person would be able to work the invention. For example, there is usually a high level of doubt that a new chemical compound will cure cancer. This is because most chemical compounds don't cure cancer, and some experiments and data are usually needed to establish any level of likelihood that a chemical compound will cure cancer. There is consequently often a high level of underlying doubt that a randomly selected chemical compound will have any particular therapeutic effect. This doubt can be substantiated by the verifiable fact that most chemicals don't, in fact, cure cancer. Therefore, in order to satisfy the sufficiency requirement, more evidence is needed to support a claim for a therapeutic use invention than would be needed to satisfy the sufficiency requirement for a mechanical invention. 

The higher level of underlying doubt surrounding therapeutic use inventions finds its expression in the plausibility test. Thus, in order for a therapeutic use invention to be sufficiently disclosed, there must be sufficient information in the application as filed to render the therapeutic use "technically plausible" (CLBA, II-C-7.2.2(a)) ("therapeutic use plausibility"). In other words, the applicant must provide sufficient evidence to overcome the high level of underlying doubt that a new drug will have a therapeutic effect. 

Critically, therefore, the plausibility test is not a higher sufficiency bar for therapeutic inventions. The sufficiency requirement, of there not being substantiated doubt that the invention will work, remains the same. What changes for therapeutic inventions is just the underlying level of doubt with respect to the invention, and thus the amount of evidence needed to overcome this doubt. 

The recent decision T 1571/19 considered the sufficiency for a therapeutic use claim, making use of the plausibility test. The patent as granted (EP2914124) claimed a fish food for use in the treatment of diseases in fish. A skilled person would know that most fish food does not treat or prevent disease in fish, and as such there was a high level of underlying doubt with respect to the invention. However, the patent included data for a trial in which two example compositions were administered to fish. The Opponent argued that whilst the data showed some beneficial effects to begin with, these faded to below statistical significance, and so the claimed therapeutic effect was not plausible. However, the Board of Appeal were satisfied that the initial beneficial effects observed contributed to an overall picture that made the claimed therapeutic effect credible. For the Board of Appeal, the Opponent was unable to point to evidence of serious doubts with respect to the claimed therapeutic effect in view of this evidence. The claims were thus found sufficiently disclosed in view of the plausible therapeutic effect. Plausibility equated to a lack of doubts, substantiated by verifiable facts, that the skilled person would be able to work the invention. 

Whole range plausibility (Wind turbines, T 0500/20)

Another type of invention for which there may be a higher level of underlying doubt about whether the invention can be worked by a skilled person are inventions involving broadly claimed features. These broad features may be broad ranges of parameter values, functional features, or a broad genus of compounds. In such cases, there may be a high level of underlying doubt that a skilled person would be able to work the invention across the full scope of the broadly claimed feature (CLBA, II-C 5.4). For an invention relating to a broad range or class of compounds for which there is this high level of underlying doubt, the concept of plausibility is again employed. Thus, in order for an invention comprising a broadly claimed feature to be considered sufficiently disclosed, the application as filed must provide sufficient evidence to make it at least plausible that a skilled person would be able to work the invention across the whole range of the claim (CLBA, II-C 5.4) ("whole range plausibility"). 

In most cases, one example is sufficient

The Board of Appeal decisions in T 0500/20 and T 2773/18, both relating to wind-turbines, confirmed that whole range plausibility only applies to certain types of invention. When considering the sufficiency of the claim, the Board of Appeal found that the whole range plausibility test should only be applied to inventions in which a central aspect of the claimed invention is a range of compositions or of parameter values, e.g. inventions primarily in the chemical field for which there is a high level of underlying doubt that a skilled person could work the invention across the whole range. By contrast, as stated by the Board of Appeal in T 0500/20, "[i]n claimed inventions that do not involve a range of parameter values or compositions basing an argument of insufficiency on this approach is inappropriate and can be rejected offhand for that reason."

In this Kat's view, therapeutic use plausibility and whole range plausibility are clearly synonymous concepts. In both cases, the concept of plausibility is introduced when there is a higher level of underlying doubt about an invention. Similarly, in both cases, the sufficiency test of whether there are substantiated doubts about the invention remains the same. The concept of plausibility is thus employed in cases where there is a higher level of underlying doubt in the field of the invention.

Plausibility in inventive step

The EPO also employs the concept of plausibility in the inventive step analysis of certain types of invention. But how does a concept relating to the sufficiency of evidence find its way into inventive step analysis under Article 56 EPC? 

The answer to this question is simple: If a functional effect of an invention is explicitly specified in a claim (e.g. "wherein the drug treats the disease"), the question of whether there is sufficient evidence for this effect is considered under the heading of sufficiency. In other words, the question is whether the application as filed provides sufficient evidence such that a skilled person can work the invention (Article 83 EPC). If the functional or technical effect of an invention is not expressed in a claim, but contributes to the problem the invention purports to solve (e.g. the functional properties of a new chemical compound), the question of whether there is sufficient evidence for the technical effect is considered under inventive step (Article 56 EPC) (CLBA, I-D-4.3.1). In other words, the question becomes whether there is sufficient evidence to convince a skilled person that the invention does actually solve the problem it purports to solve (T 0939/92, G 1/03)

There is usually little doubt as to whether an invention actually solves the problem it purports to solve. In the case of a widget, the description will describe the widget and provide an example of how it works and solves the problem. For other types of invention, however, there is more doubt about whether the invention has in fact solved the problem it purports to solve. This is particularly the case where the invention as claimed specifies a broad range of parameters. For such inventions, there may be doubt as to whether the invention solves the problem it purports to solve across the whole range of the claim.

The higher level of underlying doubt about whether certain inventions solve the problem they purport to solve across the whole range of the claim again finds its expression in the whole range plausibility test. Thus, in order for an invention to be considered to involve an inventive step, the application as filed must provide sufficient evidence to make it at least plausible that the invention solves the problem it purports to solve (CLBA, I-D-4.3.1, I-D-4.3.3). Yet again, the plausibility requirement in inventive step is an expression of a higher level of doubt with respect to certain inventions and, for inventive step, whether or not they actually solve the problem they purport to solve. 

Final thoughts

Sir Robin Jacob's opined that plausibility was a Humpty-Dumpty-ish concept. In Lewis Carroll's Alice Through the Looking Glass, the character of Humpty Dumpty redefines the meaning of words with careless abandon. To Humpty Dumpty, words mean what you want them to mean when you want them to mean it, irrespective of established definitions. In this Kat's opinion, the EPO broadly speaking does not play Humpty Dumpty with the word "plausibility". At least as far as the established case law of the Boards of Appeal is concerned, plausibility has a consistent meaning in all of the contexts in which it appears (this Kat will leave the use of plausibility in the national courts for another day...).

The concept of plausibility is used consistently by the EPO as a way of acknowledging a higher level of doubt about certain types of invention. Crucially, the sufficiency test, i.e. that there are no substantiated doubts about an invention or its technical effect, always remains the same. What changes for different types of invention is the level of underlying substantiated doubt. It is therefore not surprising that the preliminary opinion of the EBA in G2/21 made reference to the test of whether there were serious doubts, substantiated by verifiable facts, that the invention in question solved the problem it was purported to have solved. The question of plausibility will always be one of whether there is sufficient evidence to overcome a high level of underlying substantiated and verifiable doubt about an invention and its technical effect. Plausibility is therefore not a new or additional requirement for patentability, but merely an acknowledgement of the technical challenge and complexity of certain categories of invention. 

Further reading

• Enlarged Board of Appeal to tackle the "Humpty Dumpty-ish" plausibility question (G2/21) (25 Oct 2021)
• Reasons for an EBA referral on plausibility, post-published evidence and problem-solution (21 Sep 2021)
• New referral expected to the EBA on the use of post-published data to support inventive step (10 Aug 2021)
• EBA hints at accepting "lack of implausibility" standard for inventive step (G2/21)