The FCJ decided that in case of doubt, features of the characterizing part are to be interpreted in such a way that they differ from the prior art which is equated with the preamble of the patent claim in the description. 

The most frequent ground for invalidity invoked in German invalidity proceedings is lack of patentability due to lack of novelty or inventiveness. Proper claim interpretation is a pivotal prerequisite for arguing this. In the proceedings at hand, the German Federal Patent court had dismissed an invalidity action on the basis of a narrow claim interpretation. The FCJ upheld the decision. 

Details of the patent at issue

The patent at issue concerned a lighting or signaling device in motor vehicles, in particular a headlamp with a ventilation system. The purpose of the patented invention was on the one hand that the interior of the headlamp be ventilated and on the other hand, water, dust or dirt be prevented from infiltrating. Therefore, the characterizing part of claim 1 of the patent at issue requires that the ventilation system of the devices form a labyrinth with a double change of direction. In the course of the grant procedure, the description of the patent at issue was amended in order to distinguish the invention from the prior art. According to the amended description, a ventilation system according to the pre-characterizing portion of the independent patent claim 1 was known to one skilled in the art from a French patent application. The plaintiff based his invalidity attack on the very same French patent application and argued that a labyrinth with a double change of direction, as required in patent claim 1, was disclosed in the French patent application.

The FCJ Judgement

The FCJ upheld the Federal Patent Court’s decision. It confirmed that prior art documents cited in the patent description may be used as an aid when interpreting a patent claim. According to the FCJ, it must be taken into account that the teaching of a patent seeks to distinguish itself from the prior art described in it. If the description of the patent cites a prior art document, this may constitute an important means of interpretation of the patent claim, in particular if the description equates the prior art with the pre-characterizing portion of the patent claim. Further according to the FCJ, in such a scenario the features of the characterizing part are unlikely to be found in the prior art from which the invention intends to distinguish itself.

Therefore, the feature of the labyrinth with a double change of direction contained in the characterizing part of the patent claim at issue must, in case of doubt, be interpreted as distinguishing feature from the French prior art document. On that theoretical basis, the FCJ concluded that the labyrinth actually shown in the French prior art document was not to be considered as a labyrinth within the meaning of the patent claim at issue. 


In German patent invalidity proceedings, the interpretation of the patent claims is crucial for the understanding of the patent’s scope of protection. On this basis, the prior art needs to be assessed. According to settled case law, an interpretation of patent claims that is narrower than the patent claim’s literal meaning is generally not allowed. The FCJ judgment seems to contradict this principle. However, one may argue that the FCJ uses the cited prior art as a mere tool to interpret determine the literal meaning of a feature and therefore does not put this principle into question.

The decision will have various practical implications. An attack on novelty based on a prior art cited in the patent’s description will in most cases be excluded if the prior art in the patent is equated with the non-characterizing portion of the patent claim. The plaintiff’s only counter-argument will then be that there is no "case of doubt" within the meaning of the FCJ judgment, i.e. that the “natural” literal meaning of the claim features does not allow a narrow interpretation.

In the present case, the FCJ did not need to examine whether the inclusion of prior art documents for the purpose of clarifying the interpretation of the claims in the course of the grant procedure could raises issues based on Art. 123 II EPC. The plaintiff had not brought forward the argument of added subject matter. However, in practice invalidity claimants may need to focus their attention on this issue in cases where the crucial prior art was added to the description in the course of the grant procedure only.

Moreover, even though in Germany different authorities answer the questions of patent infringement and patent invalidity, the invalidity proceedings can still have an important effect on infringement proceedings. The FCJ decision may provide an important argument for the defense counsel for a narrow interpretation of patent claims in infringement proceedings.