Patents are granted for inventions which are new and have an inventive step. That seems simple enough but those familiar with the European patent system will know that things can get more complicated.
European patent claims
More generally the monopoly provided by a granted patent is defined by the claims. A patent is therefore granted based on the invention as defined by the claims in the patent application which must be novel and have an inventive step with respect to the available prior art.
For a European patent, the claims are expressed in one of the official languages of the European Patent Convention (EPC) which are English, French and German.
There can be a conflict between the limitations provided by the written language and the intellectual expression of the contribution made by an inventor with respect to prior art.
Furthermore, because of the diversity in the languages in Europe, the claimed invention in the European patent must be expressed in a way that the reader can not only understand the scope of protection but also appreciate the new and inventive contribution provided by the invention.
As a result, a requirement for clarity in the claims of the European patent application is particularly carefully scrutinized by European Patent Office (EPO) examiners.
Another reason for the particularly high scrutiny of the expression of the invention in the claims is that whilst Article 84 of the EPC requires that the claims must be clear and concise and supported by the description, clarity is not one of the grounds on which a European patent can be opposed.
Furthermore, under the EPC clarity is not a ground on which a European patent can be revoked by a national court when that European patent becomes a patent right in the state for which European patent has been designated.
The oppositions procedure of the EPC allows parties (opponents) to revoke European patents. Quite often when opposing a European patent the prior art available to the opponent is, shall we say, less than perfect. However sometimes European patents are granted for claims which are ambiguous, open to interpretation, because they lack clarity.
One useful trick an opponent can make is to interpret claims which are unclear in such a way that they read on to a prior art document, so that there is an interpretation of the claimed invention, which is not new or does not have an inventive step with respect to that prior art. Therefore a European patent can be attacked by interpreting the claims in a way which renders the claims not novel or not having inventive step.
However, is there a presumption of validity provided by the EPO when assessing an opposition filed against a European patent which the EPO has granted? I have seen the EPO to be extremely careful to ensure that both sides have a fair hearing during an opposition.
What about clarity? If the examiners have granted a European patent, considering that the claims of European patent do meet the requirements of clarity, how will an opposition division consider an attack on the claims of the European patent based on an interpretation which takes advantage of a lack of clarity?
Every case is different but in my experience the opposition division will make a construction of the claims based on their understanding of the invention. This is done typically before the hearing of the opposition, when both sides present argument in person and judgment is made.
As such, once the Opposition Division has settled on a construction of the claims, they will not revisit the question of clarity.
As a result, this can mean that the outcome of opposition can be significantly affected before either party has had an opportunity to present arguments during the hearing, if the opposition division makes an interpretation of the claims, which is adverse to either the opponent or the patent proprietor.