As today there is a clearly predominant opinion among the boards that the definition of the "forbidden area" of a claim should not be considered as a matter related to Art. 83 and 100(b) EPC (T 646/13). See also chapter II.C.8.2. "Article 83 EPC and clarity of claims".

T 256/87, followed in T 387/01, T 252/02, T 611/02 and T 464/05 form part of a line of jurisprudence established between 2004 and 2007, which has not been generally followed since then (cf. nevertheless recent T 626/14 which concerns T 464/05, and even more recently T 250/15, which held that T 626/14 did not challenge the case law. T 250/15 declined to make a referral to the Enlarged Board and considered that T 626/14 and T 464/05 concerned a particular constellation in a certain technical field).

According to T 256/87 all that has to be ensured is that the skilled person reading the specification will be able to carry out the invention in all its essential aspects and know when he is working within the forbidden area of the claims. The possibilities of indirect empirical investigation referred to in the specification were, in the board's view, an acceptable solution which sufficed to fulfil the requirements of Art. 83 EPC 1973 without undue burden. This decision was followed in T 387/01, T 252/02, T 611/02 and T 464/05.

However, according to more recent decisions, the concept of 'forbidden area' was rather associated with the scope of the claims, i.e. Art. 84 EPC, than with sufficiency of disclosure (see in this chapter II.C.8.2., T 619/00, T 943/00, T 396/02, T 1033/02, T 452/04, T 466/05, T 1015/06, T 1250/08, T 593/09, T 1507/10, T 2331/11, T 2290/12, T 1811/13, T 647/15).

T 464/05 is one of a small number of decisions in which the boards found that a lack of clarity as to the scope covered by the claims resulted in insufficient disclosure for the purposes of Art. 83 EPC. These decisions have since been called into question on a number of occasions. The board in T 548/13 referred to T 2290/12, T 1811/13 and T 647/15 for a detailed discussion of the issues involved. Decision T 464/05 forms part of a line of jurisprudence established between 2004 and 2007, which has not been generally followed since then (T 646/13).

In T 626/14, the questioning of case law in T 1811/13, in particular of T 464/05, was addressed. T 1811/13 and T 647/15 did not cause the board in T 626/14 to see anything which would undermine the reasoning in T 464/05 concerning Art. 83 EPC. T 1811/13 and T 647/15 concentrated only on an individual aspect in T 464/05, namely "the area covered by the claim", without addressing the actual findings in that decision regarding Art. 83 EPC. T 464/05 drew a distinction between the two objections under Art. 83 and 84 EPC respectively and explained the significance thereof. For example, T 464/05 did not consider the boundaries of the claimed subject-matter which were the subject of T 1811/13 and T 647/15, but the lack of indications in the patent concerning the measurement of a particular parameter. In case T 626/14 (thickness of fibrous composite – variability in measurement caused by the ill-defined "surface" of the composite), according to the board, an indication of what the pressure should be, in order to enable a reliable and repeatable thickness measurement to be made, was lacking such that the skilled person would not know when a product according to the invention has been arrived at, the defined parameter lacking a sufficiently defined technical meaning within the technical field concerned. The board stated that this finding was in line with established case law (T 464/05, T 2096/12). See T 250/15.

In T 1886/06 the board emphasised that the finding in T 256/87 could not mean, conversely, that if the claims used a term undefined under Art. 84 EPC 1973 the invention necessarily became impossible to carry out within the meaning of Art. 83 EPC 1973 in the absence, in the description or the common general knowledge of the skilled person, of concrete indications towards a possible definition; doubts as to the claims' reproducibility over their entire scope had to be substantiated by verifiable facts. A mere conjecture that their scope might extend to undisclosed variants was not enough. In T 482/09, the board addressed this same issue in detail and stated in particular that whether a competitor could know that he was working within the forbidden area of the claims depended at most on whether the claims were worded clearly enough to satisfy Art. 84 EPC. Art. 83 EPC, by contrast, made no mention of the scope of protection conferred by the claims of the patent.

In T 147/12 the board stated that the appellant had shown that the uncertainty concerning the method of determination of the alkali metal content meant that the skilled person could not ascertain whether the value he would obtain was within or outside the claimed range. It was, however, not shown that as a result of that uncertainty, the skilled person would fundamentally be prevented from obtaining a polyether according to claim 1.