The concept of plausibility has emerged in numerous prosecution cases in recent years, with global trends suggesting a shift towards treating it as an additional, standalone patentability requirement.


In general, plausibility is a patentability condition, under which there must be sufficient evidence and technical knowledge in the state of the art and the teaching of a patent's disclosure to conclude that a technical problem can be solved by the proposed technical solution.

The term 'plausibility' was first introduced in the context of patentability assessments in the European Patent Office Board of Appeal's decision in Factor-9/JOHN HOPKINS (28 June 2005, T1329/04). In a nutshell, this decision questioned whether the problem to be solved (defined as isolating a further member of the Transforming Growth Factor (TGF)-Beta superfamily) had been plausibly solved considering the teachings of the application and the state of the art at the priority date.

In this case, the subject matter was TGF-9, a specific member of the TGF-Beta superfamily. The description of the application did not exhibit the structural feature that serves to establish whether a polypeptide belongs to the TGF-Beta family – that is, the seven cysteine residues with their characteristic spacing. In fact, only six cysteine residues were present.

At the priority date, there was no available evidence to show that the claimed compound was a growth differentiation factor. As such, this could only be speculated.

As the development's credibility was in doubt, the board of appeal concluded that there was insufficient evidence in the application to find that it was "at least plausible" that a solution to the technical problem had been found. Thus, the inventive step requirement was not satisfied and the appeal was dismissed.

Another relevant precedent can be found in Canadian patent law, under which the utility requirement of a claimed invention must be demonstrated or at least "soundly predicted". For a prediction to be considered 'sound', it must meet the following conditions:

  • There must be a factual basis for the prediction.
  • The inventor must have at the date of the patent application an articulable and sound line of reasoning from which the desired result can be inferred from the factual basis.
  • There must be proper disclosure.

Therefore, a prediction cannot be speculative and must be credible or plausible.

Plausibility as an additional patentability requirement

Despite this global trend, commentators have questioned whether plausibility should be considered and regulated as an additional, standalone patentability requirement which is separate from the traditional concepts of:

  • novelty;
  • inventive step;
  • sufficiency;
  • clarity;
  • utility; and
  • industrial applicability.

When the US Leahy-Smith America Invents Act entered into force in September 2012, the US patent system finally recognised first-to-file protection over first-to invent protection, which aligned with international patent systems. Under this principle, patent rights are granted to the first inventor to file a patent application claiming the patentable invention.

As an obvious result of this change, researchers and developers tend to accelerate investigation protocols to ensure a priority date. If the process is accelerated too much, the teachings on patent applications may become speculative and the embodiments or examples could be more prophetic than factual.

In some cases, the relationship between the evaluation of inventive step and the assessment of plausibility is dangerously related. However, if an expert finds a technical effect to be plausible, the invention does not necessarily lack an inventive step. In order to determine plausibility, the teachings of a patent application or patent are taken into account. These teachings could be disregarded when evaluating inventive step.

In Mexico, the law requires disclosure of the best-known method to develop the invention. Further, the description and claims must be clear. Thus, in practice, Mexican examiners deal with plausibility issues by requesting clarifications of the subject matter and the proposed solution to the technical problem.


Arguably, plausibility should not be considered an independent patentability condition due to:

  • the different criteria for evaluating plausibility;
  • the difficulty in developing clear guidelines to establish the level of credibility required to conclude that an invention is plausible;
  • the practice regarding the first-to-file provision; and
  • the overlap with other patentability requirements.

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