3.1. Determination of closest prior art in general

The boards have repeatedly pointed out that the closest prior art for assessing inventive step is normally a prior art document disclosing subject-matter 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 in this chapter I.D.3.2.). A further criterion for the selection of the most promising starting point is the similarity of the technical problem (see in this chapter I.D.3.3.). 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 in this chapter I.D.3.4. and I.D.3.5.).

In T 1212/01 the board held that the determination of the closest prior art was an objective and not a subjective exercise. It was 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.

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; see also Guidelines G‑VII, 5.1 – March 2022 version).

As closest prior art, a "bridgehead" position should be selected, which the skilled person would have realistically taken under the circumstances of the claimed invention. Among these circumstances, aspects such as the designation of the subject-matter of the invention, the formulation of the original problem and the intended use and the effects to be obtained should generally be given more weight than the maximum number of identical technical features (T 870/96; see also T 66/97, T 314/15).

In T 1450/16 the board did not agree with the assumption relied on by the appellant that, according to the basic problem-solution approach, the person skilled in the art may be entrusted with the task of selecting the closest prior art or a suitable starting point for the assessment of inventive step. It expressed the view that the person skilled in the art within the meaning of Art. 56 EPC entered the stage only when the objective technical problem had been formulated in view of the selected "closest prior art". Only then could the notional skilled person's relevant technical field and its extent be appropriately defined (see in this chapter I.D.8.1). Therefore, it could not be the "skilled person" who selected the closest prior art in the first step of the problem-solution approach. Rather, this selection was to be made by the relevant deciding body, on the basis of the established criteria, in order to avoid any hindsight analysis.

In T 1742/12 the board endorsed T 967/97 and T 21/08, in which it was found that if the skilled person had a choice of several workable routes, i.e. routes starting from different documents, which might lead to the invention, the rationale of the problem and solution approach required that the invention be assessed relative to all these possible routes, before an inventive step could be acknowledged (see also T 323/03, T 1437/09, T 308/09, T 1261/14, T 1339/14, T 259/15, T 62/16, T 1076/16). Conversely, if the invention was obvious to the skilled person in respect of at least one of these routes, then an inventive step was lacking (see also T 558/00, T 308/09, T 1437/09, T 2418/12, T 1570/13, T 62/16, T 64/16, T 2443/18). In T 967/97 it was further stated that, if an inventive step was to be denied, the choice of starting point needed no specific justification. In T 261/19 the board stated that this was because the claimed invention must then, as a general rule, be non-obvious having regard to any prior art. The board in T 1742/12 also held that a piece of prior art may be so remote from the claimed invention, in terms of intended purpose or otherwise, that it could be argued that the skilled person could not conceivably have modified it so as to arrive at the claimed invention. Such prior art might be referred to as "unsuitable". However, this did not prohibit the consideration of an inventive step assessment starting from a piece of prior art with a different purpose (see also T 855/15, T 2304/16, T 1294/16, T 2443/18, T 1112/19).

If a piece of prior art is "too remote" from an invention, it should be possible to show that the invention is not obvious to a skilled person having regard to this piece of prior art (T 855/15, T 2057/12, T 2304/16). A generically different document cannot normally be considered as a realistic starting point for the assessment of inventive step (T 870/96, T 1105/92, T 464/98, T 2383/17).

In T 176/89 the board concluded that the closest prior art comprised two documents in combination with each other. It found that, exceptionally, the two documents had to be read in conjunction; they had the same patentee, largely the same inventors, and clearly related to the same set of tests. As a rule, however, when assessing inventive step, two documents should not be combined if, in the circumstances, their teaching is clearly contradictory (see also T 487/95).

The board in T 2579/11 ruled that there was no justification for disregarding a priority application and choosing a subsequent application as the closest prior art simply because the description in the subsequent application was by and large more detailed.

Public prior use may be used as the closest state of the art (T 1464/05).

In T 172/03 the board held that the term "state of the art" in Art. 54 EPC 1973 should be understood as "state of technology", and that "everything" in Art. 54(2) EPC 1973 was to be understood as concerning the information which was relevant to a field of technology. It could hardly be assumed that the EPC envisaged the notional person skilled in the (technological) art would take notice of everything in all fields of human culture and regardless of its informational character.

However, the board in T 2101/12 considered that the interpretation of Art. 54(2) EPC given in T 172/03 was incorrect. According to the board in T 2101/12, the legislator would have used a different term if such meaning had indeed been intended. It held that the wording of Art. 54(2) EPC was clear and required no interpretation. Art. 54(2) EPC itself contains no limitation according to which a non-technical process, such as the signing of a contract at the notary's office, may not be considered state of the art.

In T 1148/15 the board pointed out that the assumption that the remaining prior art was less relevant than the item of prior art identified as the closest may turn out to be wrong, for instance if it could be convincingly shown that the skilled person would have arrived at the claimed subject-matter in an obvious manner when starting from another item of prior art but not when starting from the identified closest prior art. In that situation, or even in case of doubt, the problem-and-solution approach may have to be repeated for any prior art that also qualifies as a suitable starting point.

In T 405/14 the board stated that the notion of "closest prior art", as it had been developed by the case law of the boards of appeal, appeared to encompass two different meanings, depending on the outcome of the objection raised under Art. 56 EPC. On the one hand, when concluding that a claimed invention was inventive, the notion of "closest prior art" seemed to rely on the assumption that there existed a metric defining the distance between items of prior art and the invention, and that an invention which was not obvious from the "closest prior art" would a fortiori not be obvious with regard to all other items of prior art which, by definition, were not so close. The second meaning was often formulated in terms of a requirement for the "closest prior art" to deal with the same problem as the invention. This was intended to avoid hindsight leading to a finding that inventive step was lacking. The board concluded that here there was no requirement that the "closest prior art" be unique, because the basic rule was that an invention lacked inventive step if it would have been obvious to the skilled person, without hindsight, for any starting point.

In T 97/14 the board held that a reasoned objection of lack of inventive step must establish the state of the art and set out, in a clear and complete manner, which features of the claimed invention were known from the prior art and where those features could be found in the prior art. In other words, a proper feature mapping was required. This was all the more important when the objection relied on non-documentary prior art, because such evidence was more difficult to verify.