Art. 56 EPC 1973 requires the claimed invention, i.e. the proposed technical solution for a given technical problem, not to be obvious to a skilled person from the state of the art. If the inventive step of a claimed invention is based on a given technical effect, the latter should, in principle, be achievable over the whole area claimed (T 939/92, OJ 1996, 309; T 694/92, OJ 1997, 408; T 583/93, OJ 1996, 496).
T 939/92 (OJ 1996, 309) contained fundamental rulings on broad claims in the field of chemistry. The board held that in view of the state of the art the technical problem which the patent in suit addressed was the provision of further chemical compounds with herbicidal activity. It was necessary for all the claimed compounds to possess this activity. Moreover, the question as to whether or not such a technical effect was achieved by all the chemical compounds covered by such a claim, might properly arise under Art. 56 EPC 1973, if this technical effect turned out to be the sole reason for the alleged inventiveness of these compounds. The appellants' submission that the test results contained in the description showed that some of the claimed compounds were indeed herbicidally active could not be regarded as sufficient evidence to lead to the inference that substantially all the claimed compounds possessed this activity. In such a case the burden of proof rested with the appellants. The requirements of Art. 56 EPC 1973 had not therefore been met (T 268/00, T 1188/00, T 320/01, T 1064/01, T 924/02).
Following T 939/92 (OJ 1996, 309), the board stated in T 668/94 that the technical problem could only be taken into account in the assessment of inventive step if it could be accepted as having been successfully solved, i.e. if it were credible that substantially all the claimed compounds possessed the plant growth regulating activity. When only some and not substantially all claimed compounds exhibited a particular technical effect, the conclusion had to be that the invention as broadly defined in the independent claim was not a solution to the technical problem of achieving the given technical effect, with the consequence that the alleged technical effect of some of the claimed compounds was to be disregarded when determining the objective problem underlying the invention and thus when assessing inventive step.
In T 942/98 the problem as per the application was the preparation of improved selective herbicides. The board referred to the above-mentioned case law and did not agree with the applicant that, in the present case, he merely had to show an improved effect at the direct interface between prior art and the application in order to demonstrate, without providing further details, that such an improvement applied without qualification for the entire breadth of the claim. The appellant's position, in the board's view, amounted to allowing the applicant to decide how broad a claim could be, whether or not an improvement in the effect of all the compounds claimed was actually credible.