3.1. Determination of closest prior art in general

In accordance with the problem and solution approach, the boards have developed certain criteria for identifying the closest prior art to be treated as a starting point.

The boards have repeatedly pointed out that the closest prior art for assessing inventive step is normally a prior art document disclosing subject­matter conceived for the same purpose or aiming at the same objective as the claimed invention and having the most relevant technical features in common, i.e. requiring the minimum of structural modifications (see point 3.2 below). A further criterion for the selection of the most promising starting point is the similarity of technical problem (see point 3.3 below). In a number of decisions, the boards have explained how to ascertain the closest prior art constituting the easiest route for the skilled person to arrive at the claimed solution or the most promising starting point for an obvious development leading to the claimed invention (see point 3.4 below).

The determination of the closest prior art is therefore an objective and not a subjective exercise. It is made on the basis of the notional skilled man's objective comparison of the subject-matter, objectives and features of the various items of prior art leading to the identification of one such item as the closest (T 1212/01).

After the relevant prior art has been identified, careful consideration must be given to the question whether, in the case concerned, the skilled person, taking into account all the available information on the technical context of the claimed invention, would have had good reason to take this prior art as the starting point for further development. The term "state of the art" in Art. 54 EPC 1973 should be understood as "state of technology", and "everything" in Art. 54(2) EPC 1973 is to be understood as concerning the information which is relevant to a field of technology (T 172/03).

In T 1464/05 the board considered the features rendered available to the public by a public prior use as the closest state of the art.

The closest prior art must be assessed from the skilled person's point of view on the day before the filing or priority date valid for the claimed invention (T 24/81, OJ 1983, 133; T 772/94, T 971/95, Guidelines G-VII, 5.1 – June 2012 version).

Unidentified "prior art" cited in the patent does not form part of the state of the art within the meaning of Art. 54(2) EPC 1973 and cannot be used for basing an assessment of inventive step (T 671/08).

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