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Plausibility – An Important Consideration

9 June 2021

The concept of plausibility is not mentioned in either the UK Patents Act or the European Patent Convention. However, it has become an increasingly common talking point and has featured in numerous decisions of both the UK courts and the Boards of Appeal of the European Patent Office. The requirement for “plausibility” can be considered as an attempt to exclude from patent protection theoretical inventions which are based, at the time of filing the patent application, purely on assertion.

In both Europe and the UK, a patent cannot be invalidated for lacking plausibility as such. The concept is predominantly raised in connection with either sufficiency of disclosure or inventive step, each of which is required for patent validity. It has evolved from case law in these areas, and it is important to be aware of the requirements, to ensure that they are met when a patent application is prepared.

Plausibility is assessed based upon the information in the patent application as filed, together with the skilled person’s common general knowledge at the time of filing. In essence, for an invention to be considered ‘plausible’, the technical effect of the invention must be demonstrated by the information provided in the patent application. In the chemical and life sciences, this will usually be via experimental data pertinent to the technical effect. If a technical effect is foreseeable or indisputable, experimental data may not be needed. In such a case, however, the foreseeability of the technical effect may render the invention obvious. Essentially, the more unexpected the technical effect, the more important the presence of technical evidence in the patent application as filed.

It is important to note that a lack of plausibility cannot be remedied after a patent application is filed.  Whilst the UKIPO and the EPO are willing to consider additional, post-filing evidence in support of inventive step during prosecution (e.g. to support a technical advantage of the invention compared to the prior art), such consideration will only be given once the plausibility hurdle has been overcome based on the content of the application as filed.  Patent applications have therefore been refused in cases where no experimental data was included in the application as filed, despite later evidence being filed to demonstrate that the invention did indeed perform in the manner asserted.

When deciding on the filing strategy of a patent application in the chemical and life sciences, determining how much technical evidence is required on filing to overcome the “plausibility” hurdle requires careful attention.

Given the competitive nature of this sector, there is a need to strike a balance between filing too soon with limited (or no) supporting evidence, and filing too late and potentially losing the advantage over competitors. For instance, filing too early without sufficient data to demonstrate the technical effect of the invention can leave the patent vulnerable for lack of plausibility. However, where the collection of experimental data will be time consuming, such that there is a delay in  filing a patent application, there is a risk of someone else filing an earlier application for the same (or a similar) invention.

Whilst the case law in this area is continuing to expand, the ‘threshold’ for plausibility is not currently well-defined. It seems that the hurdle is intended to be a low one, such that a limited amount of relatively rudimentary data should suffice in many instances. To avoid potential problems in this area, we would generally not recommend filing patent applications in the chemical and life sciences containing no data.


Georgia Mann

Life Sciences & Chemistry Group

This publication is a general summary of the law. It should not replace legal advice tailored to your specific circumstances.

© Withers & Rogers LLP June 2021