3.4. Same purpose or effect

According to established case law (see for example T 2057/12, T 1148/15, T 96/20, T 2443/18, T 335/20, T 485/21, T 553/23), a central consideration in selecting the closest prior art is that it must be directed to the same purpose or effect as the invention, otherwise it cannot lead the skilled person in an obvious way to the claimed invention. In T 14/17 the board held that if this purpose was not explicitly set out or could not be inferred from the claims, the question to be answered was what, in the light of the application or patent as a whole, was to be achieved by the claimed invention.

According to T 606/89 the closest prior art for the purpose of objectively assessing inventive step is generally that which corresponds to a similar use requiring the minimum of structural and functional modifications (see also T 574/88, T 686/91, T 834/91, T 482/92, T 59/96, T 650/01, T 1747/12, T 529/20).

In T 273/92 the board confirmed the established case law that a document could not qualify as the closest prior art to an invention merely because of similarity in the composition of the products; its suitability for the desired use of the invention also had to be described (see also T 327/92). According to T 506/95 the closest prior art was the art most suitable for the purpose claimed by the invention, not the art superficially showing structural similarities. Ideally, that purpose should already be mentioned in the prior art document as a goal worth achieving (T 298/93, T 859/03, T 1666/16, T 58/19). The aim was that the assessment should start from a situation as close as possible to that encountered by the inventor, avoiding ex post facto considerations. The real-world circumstances had to be taken into account. If it was not clear what the closest prior art was, the problem-solution approach should be repeated taking possible alternative starting points (T 710/97, T 903/04, T 2123/14).

In T 2255/10 the board (with reference to T 482/92) stated that in establishing the closest prior art, the question to be asked was, what, in the light of the application as a whole, would be achieved by the invention as claimed. Statements of purpose must be read in conjunction with the claims. Merely inserting such a statement into the description does not entitle an applicant effectively to "veto" any inventive-step objection based on a document which is unrelated to this purpose, if it is not plausible that the invention as claimed would actually achieve the stated purpose.

In T 53/08 the board, in deciding whether document (1) or document (10) had to be regarded as the closest prior art, considered the patent's objective, which was to develop the highly effective herbicidal ingredient of formula (A1) in such a way that it did not significantly damage crops when used in a concentration with herbicidal effect. The natural starting point for the invention was therefore the document disclosing the active ingredient of formula (A1).

In T 2571/12 the board held that, in the case of claims directed to medical uses, the closest prior art is usually a document disclosing the same therapeutical indication.

In T 1076/16 the board considered that a piece of prior art could not be immediately ruled out as a possibly suitable starting point merely because it had a different purpose from the invention or fewer technical features in common with the invention than other, seemingly "closer" prior art. Depending on how the criteria "similar purpose" and "common features" were weighed up against each other, there were often several reasonable starting points, each offering a different route that might lead to the invention without the need for hindsight. The board endorsed the case law developed in a number of decisions (T 405/14, T 2057/12 and T 1742/12) that, for a finding of a lack of inventive step, it was enough that the invention was obvious to the skilled person from the prior art in the light of just one of those routes (see also T 335/20).

In T 1148/15 the board held, in response to a misunderstanding of the case law by the appellant, that if the closest prior art also had to disclose the purpose or effect of the distinguishing feature(s), it would mean that only items of prior art which contained a teaching towards the distinguishing feature(s) would qualify as the closest prior art. This was not required by the problem-and-solution approach because the teaching towards the distinguishing feature(s) may come from another item of prior art or from the skilled person's common general knowledge. In other words, the closest prior art does not have to disclose all the problems solved by the claimed invention. In particular, it does not have to disclose the objective technical problem, which is determined only in the next step of the problem-and-solution approach.

In T 513/19 the board was of the opinion that when assessing the suitability of a document as the closest prior art, the criterion of having the same purpose also included that the patent and the closest prior art should deal with the same product. In the case in hand D1 and the patent shared the same purpose of providing a cappuccino beverage, whereas D4 related to a chocolate beverage and was not cited by the appellant to be combined with D1. In view of the similarity of the purpose and the objective when comparing the patent and D1, D1 was a suitable starting point in the discussion of inventive step.

In T 1188/20 the appellant had selected D2 as the closest prior art essentially because it required the minimum of structural modifications to arrive at the subject-matter of claim 1. The board held this approach would be allowable if D2 were a realistic starting point for a further development in the field of insulating materials. However, D2 had no connection whatsoever to the technological field of the opposed patent and was thus not considered to be a reasonable starting point.