Posted on 24/1/2023

Commas causing chaos in patent claims

A European patent has recently been revoked due to a lack of commas to denote a clause.

A European patent has recently been revoked due to a grammatical error in the patent claims.  This error, a lack of commas to denote a clause, led to the patent being revoked as it was deemed to extend beyond what was disclosed in the patent application as filed.

Under European patent law, the claims of a patent define the extent of protection that the patent owner is entitled to.  In this case it was confirmed that while the description and any drawings can serve to help interpretation of the claims, where the meaning of the claims is clear, the claim meaning takes priority.  This is irrespective of what the patent applicant intended to claim.

As such, it is very important to get the claims right and ensure that they unambiguously cover exactly what you intend to protect.  This case demonstrates the importance of checking claim wording carefully for alternative meanings and how a simple error can ultimately lead to loss of a patent.

Summary of the case and decision

The case relates to a European patent for a CT scanner that was granted but then opposed by a third party.  The main patent claim included the following wording which described the body of a rotary joint in the CT scanner:

said body having a free inner bore holding a capacitive data link”.

The patent description and drawings all described a body that:

has a free inner bore; and,

is holding a capacitive data link.

The patent was opposed on the basis that this part of claim actually meant:

the body has a free inner bore; and,

the inner bore is holding a capacitive data link.

As the patent application as filed did not describe a body with a free inner bore and a free inner bore holding a capacitive data link, the opponent argued that the patent should be revoked on the ground of added subject-matter.

Initially, the patent owner successfully argued that the opponent was wrong, however, on appeal the opponent was ultimately successful.

In reaching their decision, the Board of Appeal considered that the “person skilled in the art” would interpret the claims as described by the opponent, and not as the patent applicant had intended the claims to mean.  This was in part because they only considered the patent description to be relevant when determining the meaning of ambiguous terms, however, there were no such ambiguous terms in the claim.  In addition, the Board found no reason to avoid the unintended meaning, because it was technically sensible and not illogical and also as the patent description did not specifically exclude the unintended meaning.

The patent owner attempted to resolve the situation by correcting the claim wording to add a couple of commas as follows:

said body, having a free inner bore, holding a capacitive data link”.

However, partly because the phrase “having a free inner bore” had been introduced by the patent examiner (who tweaked the language when allowing the application) and not by the applicant, the Board of Appeal refused the request for a correction of an error.  This is because you can only correct errors in documents filed with the European patent office, so you can’t correct an error originating in a document from the European patent office themselves.

Another important aspect of European patent law is that you can’t change the scope of protection after grant, except by limiting its scope.  As the patent had already been granted, then, changing from the unintended meaning of:

the body having a free inner bore [and the inner bore is] holding a capacitive data link,

to the intended meaning of:

the body, having a free inner bore, [and the body is] holding a capacitive data link,

is not allowable because the corrected claim covers subject-matter that the granted claim does not.  So, the applicant was additionally prevented from adding in the two commas to denote a clause and recover the intended meaning under added subject-matter rules.

The patent owner was then in a position that they could not escape from, because of the added subject-matter, error correction and claim broadening rules mentioned above.  Consequently, the patent was revoked.


Claims are the most important part of a patent and should therefore be carefully checked to ensure they cover the right subject-matter and are not open to misinterpretation.  This applies both before filing a patent application as well as before grant of the patent, especially where the patent examiner has suggested changes to the claim wording, because the ultimate responsibility lies with the applicant.

This decision shows how an error in claim grammar can spiral into the loss of a patent due to an unintended claim meaning, even when the rest of the patent doesn’t support this meaning and it was not what the patent applicant intended. If you have any questions about this please contact one of our attorneys.

Wilson Gunn