IP Information & News

EPO discusses choice of closest prior art

The assessment of inventive step of a claimed invention is a key part of the patent prosecution process. The European Patent Office (EPO) is no different from any other office in attempting to assess inventive step using a rigorous legal test. The preferred legal test at the EPO is the often discussed ‘problem-and-solution’ approach.

There are three main stages of this approach:

  • Determining the closest prior art.
  • Establishing the objective technical problem solved by any features of the claimed invention that are not disclosed by the closest prior art.
  • Considering whether or not the claimed invention is obvious over the closest prior art.

The consideration of the closest prior art is therefore fundamental to the correct application of the problem-and-solution approach. The EPO has recently discussed the criteria against which the closest prior art should be chosen when applying this approach.

The EPO’s own guidelines are quite clear about what the criteria should be, in that it sets out that the closest prior should be that single reference which discloses the combination of features which constitutes the most promising starting point for a development leading to the invention. According to the EPO’s guidelines, the selection of the closest prior art is guided primarily by the consideration of whether the document in question is directed to a similar purpose or effect as the invention — or at least the consideration of whether the document belongs to the same (or a closely related) technical field as the claimed invention. That is to say, according to the EPO, the closest prior art should provide a promising starting point for arriving at the invention. Only against such a starting point can the inventive step of an invention really be tested.

The EPO therefore appears to take a sensible approach to this matter — but there’s always real frustration, particularly in cases related to software, when the examiners at the EPO seem to go against this sensible teaching by choosing a piece of prior art which appears to be entirely unrelated, or have only a tenuous link to the invention.

In software cases, it’s not unknown for an Examiner to cite a ‘commonplace’ data processing system against a claim as the closest prior art. This inevitably leads to conclusions about inventive step which are trite and trivial and do nothing other than prolong prosecution.

In case T 1379/11, the Board of Appeal held that the closest prior art must be a realistic starting point which must be a logical choice for the skilled person if they are dealing with the kind of matter to which the invention relates.

As ever, the word ‘realistic’ is open to interpretation and some may remark that it’s hardly a profound departure from the guidelines the EPO provided. However, in reading this decision, the reader will notice that the consideration of what is a ‘realistic’ choice of closest prior art changed the document the Board of Appeal used in its consideration of inventive step — although it did not overturn the decision under appeal.


The term ‘realistic’ can be interpreted many ways but, using a dictionary definition, its meaning can be summarised as representing things in a way that is accurate and true to life. If this meaning is adopted, this decision suggests that the closest prior art should be one which the skilled person would consider in real life.

Whilst we are sure the EPO is not trying to give the skilled person too many human qualities, it affords the power to decide on what is a realistic starting point for solving a problem. This, in turn, logically provides the skilled person with the power to decide on what is not a realistic starting point for solving a problem.

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