A Cautionary Comma Calamity

March 28, 2023
By: Denis V. Keseris and Nicole LaBerge

The Boards of Appeal of the European Patent Office (EPO) recently published a decision (T 1473/19) in which they revoked a patent due to a missing pair of commas in a claim. The decision serves to remind North American applicants and patent practitioners of just how perilous the EPO’s strict claim amendment practices can be.


In 2017, Schleifring GmbH (the Patentee) obtained EP patent no. 262134 A1 relating to a contactless rotary joint for use, for example, in a computerized tomography (CT) scanner. The patent provides an improved contactless rotary joint which minimizes the risk of interference between the rotating transformer and the capacitive data link by shielding electrical and/or magnetic fields generated by the rotating transformer.

The following feature was introduced by the Examining Division in the “Druckexemplar” (approved text) accompanying the notice of allowance (Rule 71(3) EPC).

“said [rotary joint] body having a free inner bore holding a capacitive data link”

Siemens Healthcare GmbH (the Opponent) filed an opposition including the ground that the added feature contravened Article 123(2) EPC, which holds that a European patent or application cannot be amended in such a way as to contain subject matter which extends beyond the content of the application as filed. The crux of Siemen’s argument rested on the interpretation of the added feature. Namely, whether:

  1. the body has a free inner bore and this bore holds a capacitive data link

(i.e., the inner bore holds the capacitive data link)


  1. the body has a free inner bore and, additionally, the body holds a capacitive data link

(i.e., the body holds the capacitive data link)

The Opponent argued that the capacitive data link is held by the free inner bore (interpretation a) above) and since the application as filed disclosed only a single example in which the capacitive data link is held by the body, the claim violated Article 123(2) EPC. The Opposition Division rejected the Opponent’s argument and held that the basis of the claims should be interpreted in light of the description. Moreover, the claim should be read as: “said body, having a free inner bore, holding a capacitive data link”.

The Opponent appealed requesting that the Opposition Division’s decision be set aside, and that the patent be revoked.

The Board of Appeal’s Decision

The Board of Appeal agreed with the Opponent, set aside the decision, and revoked the patent.

In particular, the Board held that the expression in question is constructed as a series of noun groups (“said body”, “a free inner bore”, “a capacitive data link”) separated by present participles (“having”, “holding”).[1] Moreover, in the absence of any comma and any coordinating conjunction separating the various terms, the skilled person, on a plain reading of this expression, would simply consider the subject governing each present participle to be the bound group immediately preceding it, following the rule that modifiers are generally placed next to the word they modify.[2]

Accordingly, the skilled person would arrive at the construction that the body has a free inner bore and that this bore holds a capacitive data link (i.e., interpretation a)).[3]

The Board further held that this interpretation was sensible and plausible. A “free inner bore” form in a body, in the context of a rotary joint as defined in claim 1, is not limited to an empty space or hole, but includes the physical surface that surrounds and defines the hole. It is therefore not illogical that a bore may “hold” a component via the interaction between this component and this physical surface, even if this surface is at the same time an inner surface of the body in which the bore is formed. Contrary to the Patentee’s argument, there was no contradiction in the fact that the free inner bore may “hold” a capacitive data link. Moreover, a skilled person when faced with this expression would have no reason to depart from interpretation a) for technical reasons.

A Very European Trap

The patentee submitted three possible auxiliary amendment requests to correct the deficiency; however, the Board rejected them all. They held that none of them were allowable because they would bring the disputed expression of claim 1 in line with interpretation b) above. Namely, that the free inner bore holds a capacitive link. Such amendments would extend the patent protection beyond the scope of what was granted and therefore violate Article 123(3) EPC which states “the European patent may not be amended in such a way as to extend the protection it confers”. As such, this amendment fell foul of what is known in Europe as the “123(2)/123(3) trap” which essentially prevents the broadening of a claim (Article 123(3) EPC) by way of the removal of a limiting amendment that introduced subject matter which extended beyond the content of the application as filed (Article 123(3) EPC).

The Board also rejected the Patentee’s request for correction under Rule 139 EPC. They stated that Rule 139 EPC only allows correction of linguistic errors, errors of transcription and mistakes “in any document filed with the EPO”. Since the error was not in a document filed with the EPO, it was not permitted.

Punctuation Matters. Period.

The above decision reminds European practitioners to be acutely aware of the EPO’s strict claim amendment practices, even when the EPO itself is making the amendments! Particular attention should be paid to the introduction of limiting claim features that do not find verbatim basis in an application as originally filed. As Lynne Truss notes in her book Eats, Shoots & Leave: The Zero Tolerance Approach to Punctuation, “[p]roper punctuation is both the sign and cause of clear thinking”. One could argue that the same is true for proper punctuation being the sign and cause of clear patent claims. Given Europe’s uncompromising practices when it comes to claim amendments, we would all do well to take heed of this cautionary tale.


[1] T 1473/19 at para 4.2.

[2] Ibid.

[3] Ibid at para 4.3.

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