There is now 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). Decision T 626/14 does not call this into question, according to the board in T 250/15. See also in this chapter II.C.6.6.4 "Forbidden area of the claims".

When undefined parameters are used in the claims and no details of the measuring methods are supplied, the question arises whether there is a problem with respect to Art. 83 or Art. 84 EPC. The answer to this question is important because in opposition proceedings the patent can be examined for its compliance with Art. 83 EPC without any restriction. Compliance with Art. 84 EPC is however examined only in cases where there has been an amendment. In its decision G 3/14 (OJ 2015, A102) the Enlarged Board reiterated the principles governing the extent to which patents amended in opposition proceedings can be examined for compliance with Art. 84 EPC. A more detailed account of its decision can be found in chapter II.A.1.4.

In some decisions (for example, T 123/85, T 124/85, T 172/87, T 358/88, T 449/90, T 148/91, T 267/91, T 697/91, T 225/93, T 378/97, T 387/01, T 252/02, T 611/02, T 464/05, see recently T 626/14) the absence of information in the application on methods for measuring undetermined parameters in the application was considered a problem with respect to Art. 83 EPC. These were all inter partes proceedings. This problem has also been addressed with reference to Art. 83 EPC in ex parte proceedings, (see T 122/89 of 5 February 1991 date: 1991-02-05 and T 503/92). Other decisions have considered this a problem with respect to Art. 84 EPC, for example, in T 860/93 (OJ 1995, 47), also ex parte proceedings, it was decided that the absence of methods for measuring a relative quality in the claim was a problem with respect to the clarity of the claim. See also T 230/87, T 176/91 of 10 December 1992 date: 1992-12-10, T 917/92, T 299/97, T 439/98, T 413/99, T 930/99, T 960/98, T 619/00, T 943/00, T 344/01, T 563/02, T 1033/02, T 208/03, T 882/03, T 452/04, T 1316/04, T 466/05, T 1586/05, T 859/06. Some of these decisions are discussed further below.

According to T 593/09 (see Headnote about ill-defined ("unclear", "ambiguous") parameter) the requirement of sufficient or "enabling" disclosure in the sense of Art. 83 EPC is different from and independent from the clarity requirement pursuant to Art. 84 EPC. The board saw this distinction as underlying the decision in T 1062/98. The board in T 593/09 saw a distinction between the meaning of "clear" in Art. 83 EPC, which concerns the disclosure (the "technical teaching") of the application or the patent on the one hand, and in Art. 84 EPC, where that expression relates to the claims, which "shall define the matter for which protection is sought" on the other hand. In short, there is a distinction between clarity of what has been disclosed and clarity of what is claimed. The board found that this distinction was not always properly made, in particular in respect of so called "ambiguous parameters", i.e. parameters present in the description and/or claims, whose exact definition and/or applicable measuring method remained doubtful. For example, numerous decisions of the boards of appeal have as a relevant criterion for the sufficiency of a disclosure containing an ill-defined parameter, whether the skilled person knows if he is working within or outside of the scope of the claim (see T 256/87, T 387/01, T 252/02 and T 18/08). It was however, not always apparent from the reasoning of these decisions whether or not this criterion was meant to be the sole or the decisive one.

In T 943/00, the board disagreed with T 256/87, finding that the concept of "forbidden area" was associated with the scope of the claims, i.e. Art. 84 EPC 1973, rather than with sufficiency of disclosure. The board in T 466/05 agreed, also stating that a distinction should be made between the requirements of Art. 84 EPC 1973 and those of Art. 83 EPC 1973, and that with respect to sufficiency, the relevant question was whether the patent in suit provided sufficient information which enabled the skilled person when taking into account common general knowledge to reproduce the invention (see also T 472/14). Numerous decisions (e.g. T 960/98, T 619/00, T 396/02, T 1033/02, T 452/04, T 466/05, T 1586/05, 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 548/13), have also interpreted the statement, "knowing when working within the forbidden area of the claims" formulated in T 256/87 as addressing the question of the limits of protection conferred by the claims, and thus relating to a requirement of Art. 84 EPC rather than of Art. 83 EPC. See also in this chapter II.C.6.6.4 "Forbidden area of the claims".

The board in T 2290/12, having summarised the case law on sufficient disclosure versus clarity, concluded that a broad consensus, or at least a prevailing view, had now been reached that the skilled person's ability to establish whether or not subject-matter fell within the claimed scope was a requirement for clarity and not for sufficient disclosure (see also similar decisions T 1811/13 and T 647/15). All the respondent's objections under Art. 100(b) EPC 1973 were concerned with the precise scope of protection conferred and so, in fact, clarity objections.

If it is argued that insufficiency arises from a lack of clarity, it is generally not sufficient to establish a lack of clarity of the claims in order to establish insufficiency of disclosure. Rather, it is necessary to show that the patent as a whole does not enable the skilled person, relying on the description and on his common general knowledge, to carry out the invention (T 417/13 citing T 1811/13 and T 646/13).

For the board in T 548/13 (security elements for security papers and value documents), the argument put forward by one party that the skilled person did not know what the back of a face should look like, or at least which of several options to select, confirmed its view that it was in fact dealing with a clarity objection. The case law on parameters, which included T 815/07, did not apply because the feature in question did not involve any quantitative parameter for which the method of measurement might be insufficiently disclosed. It was instead a purely qualitative feature which could be determined without any measuring in the strict sense. The board could not see why the skilled person would be unable to equip a security element with security features showing different views of the same image, so it appeared that the opposition division had underestimated that person's abilities in this respect.

The board in T 626/14 (thickness of fibrous composite – variability in measurement) considered it important to mention that T 1811/13 and T 647/15 – with essentially identical reasoning as regards Art. 83 EPC – sought to question the way in which Art. 83 EPC objections were reasoned in decisions such as T 464/05. Yet, T 1811/13 and T 647/15 themselves 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 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. More recently in T 250/15 the board 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.

In T 646/13 the opponent's request for a referral hinged on an alleged contradiction between decisions T 1811/13 and T 464/05 on the issues of clarity of the claims and sufficiency of disclosure. The board concluded that these cases concurred in that an unclear definition of the boundaries of the claim pertained to Art. 84 EPC 1973. Application of the principles set out in decisions T 464/05 and T 1811/13 would not lead in the circumstances of T 646/13 to different results. Finally and more importantly, as explained in decision T 1811/13, decision T 464/05 forms part of a line of jurisprudence established between 2004 and 2007, not generally followed since then. There is now 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 1973, the alleged contradiction between decisions T 464/05 and T 1811/13 does not exist. Rather than being in conflict, these decisions illustrate a development of the case law on a particular question over an extended period of time.

The board in T 608/07 found the issue before it with regard to sufficiency of disclosure was quite similar to the situation in T 256/87, both concerning an insufficiency which arose through ambiguity. Although the board accepted that, depending upon the circumstances, such an ambiguity might very well lead to an insufficiency objection, it should be borne in mind that this ambiguity also related to the scope of the claims, i.e. Art. 84 EPC 1973. Since, however, Art. 84 EPC 1973 was in itself not a ground of opposition, care had to be taken that an insufficiency objection arising out of an ambiguity was not merely a hidden objection under Art. 84 EPC 1973. The board was convinced that, for an insufficiency arising out of ambiguity, it was not enough to show that an ambiguity existed, e.g. at the edges of the claims. It would normally be necessary to show that the ambiguity deprived the person skilled in the art of the promise of the invention. It went without saying that this delicate balance between Art. 83 and 84 EPC 1973 had to be assessed on the merits of each individual case.

According to T 593/09, the same rationale underlay both T 608/07 and T 815/07 (and also Kirin-Amgen Inc v. Hoechst Marion Roussel Ltd [2004] UKHL 46 of the United Kingdom House of Lords); namely, where a claim contains an ill-defined ("unclear", "ambiguous") parameter and where, as a consequence, the skilled person would not know whether he was working within or outside of the scope of the claim, this, by itself, is not a reason to deny sufficiency of disclosure as required by Art. 83 EPC. Nor is such a lack of clear definition necessarily a matter for objection under Art. 84 EPC only. What is decisive for establishing insufficiency within the meaning of Art. 83 EPC is whether the parameter, in the specific case, is so ill-defined that the skilled person is not able, on the basis of the disclosure as a whole and using his common general knowledge, to identify (without undue burden) the technical measures (e.g. selection of suitable compounds) necessary to solve the problem underlying the patent at issue.

The board in T 1526/09 observed that it had been decided in T 593/09 that a claim containing a vague or ambiguous parameter preventing the skilled person from knowing whether he was working within or outside the scope of the claim did not result in insufficient disclosure of the invention. The crucial question in deciding on sufficiency of disclosure was whether the parameter was so vaguely defined that the skilled person could not identify, in the patent as a whole, the measures required to solve the underlying problem. The parameter at issue had been essential to preparing the product. In T 1526/09 the vague definition of chargeability affected the clarity of the claimed subject-matter but did not prevent the skilled person from preparing the claimed product.

The board, in T 1305/15, was aware that according to case law, uncertainties in the measurement of a parameter did not necessarily amount to an insufficiency objection but might merely represent a hidden clarity objection under Art. 84 EPC (T 608/07). This might be the case for example when no measurement method was specified in the patent and different known methods were available to the skilled person, possibly leading to different results (T 1768/15). However, when the claimed parameter (the ZP in T 1305/15) is crucial for solving the problem underlying the invention, the method used to measure it should produce consistent values, such that the skilled person will know when carrying out the invention whether what he produces will solve the problem or not (T 815/07). Due to the severe lack of information concerning the ZP measurement method, the ZP on the inner membrane surface was so ill-defined that the skilled person, when trying to reproduce the hollow fiber membrane according to the contested patent, was at a loss whether or not the produced membrane was able to solve the problem underlying the invention. This posed an undue burden on the skilled person, depriving him of the promise of the invention, and thus amounted to insufficiency of disclosure (citing T 593/09).

In T 378/11, the values disclosed in claim 1 referred to the average particle size. No proof had been submitted by the appellants/opponents that the lack of any indication as to the precise kind of average particle size hindered the skilled person from carrying out the invention at issue. The board found that the skilled person could select those kinds of mean values falling within the range 10-500 mym in order to prepare a composition according to the invention at issue. Whether or not the use of two kinds of mean values would lead to different results was a matter of clarity, rather than sufficiency of disclosure.

In T 1608/13 the board first stated that clarity (Art. 84 EPC) and sufficiency of disclosure (Art. 83 EPC) were two distinct requirements of the EPC, as reaffirmed in recent case law (T 2290/12, point 3.1 of the Reasons, citing T 608/07, point 2.5.2 of the Reasons). The board did not see how – and the respondent (opponent) did not explain why – a potential lack of clarity deriving from the claim definition of the sieving coefficient in the presence of whole blood could have a major impact on implementing a membrane which solved the specific technical problem that the invention aimed to solve. Hence, using the wording of T 608/07, with which the board concurred, such a potential lack of clarity would not deprive the skilled person of the promise of the invention, and would not result in insufficiency of disclosure. As far as lack of clarity is concerned, it is not a ground for opposition.

In T 2399/10, none of the cited documents, which had been published before the contested patent's priority date, used the expression "form factor". It appeared only in documents not forming part of the prior art under Art. 54(2) EPC. The patent thus did not disclose how to produce the alumina particles needed to obtain the claimed composition. This situation differed from cases where the features of the end product described in the patent were not clearly defined, which frequently resulted in a lack of clarity. Instead, it was a starting material which had not been here defined clearly enough. Since there was therefore inadequate information to select the starting material, the claimed composition could not be produced. This typically meant there was insufficient disclosure.

In T 287/10, the claimed invention concerned a composition for the surface treatment of paper, paperboard or the like. The respondent (opponent) alleged that the invention was insufficiently disclosed; the gist of its objection was that the end values of the size range of the synthetic silica nanoparticles of the claimed composition were ambiguous. The board disagreed. Exactly the same point of law had been considered and answered by the same board in the same composition in T 1414/08, with respect to another parameter common in the art, namely tensile strength. The reasoning and the conclusion drawn in decision T 1414/08 was, in the board's opinion, directly applicable to the case at issue, where the undefined parameter was the particle size. Hence, the ambiguity of the end values of the size range of the nanoparticles comprised in the claimed composition, just as in decision T 1414/08, was "not a matter to be addressed under Art. 83 EPC but a question of Art. 84 EPC". The board found the invention sufficiently disclosed.

In T 1055/92 (OJ 1995, 214) the examining division had rejected the patent application under Art. 84 EPC 1973 because in the claim it was not clear how certain values were to be computed. The board held that the requirements of Art. 84 EPC 1973 should be clearly distinguished from the requirement under Art. 83 EPC 1973. Under Art. 83 EPC 1973, sufficient disclosure was required of a European patent application, i.e. of the application as a whole, comprising the claims, together with the description and the drawings, but not of an individual claim as such. A claim, on the other hand, had to comprise the essential features of the invention (T 32/82, OJ 1984, 354); the essential features should comprise those features which distinguished the invention from the closest prior art. The primary function of a claim was to set out the scope of protection sought for an invention, which implies that it is not always necessary for a claim to identify technical features or steps in detail (see also T 713/98).

According to T 882/03, slightly varying results obtained when using different mathematical models for the calculation of the intrinsic viscosity did not prevent a person skilled in the art from carrying out the invention but were rather related to the question of whether the matter for which protection was sought was sufficiently defined in accordance with Art. 84 EPC 1973.

In T 430/10 if the alleged lack-of-clarity was that a feature could be interpreted narrowly or broadly, the sufficiency requirements were met if the skilled person, applying the broad interpretation, was at least able to carry out all embodiments covered by the claims. In the case at issue, the requirements were fulfilled.

In T 378/97, the board noted that sufficiency of disclosure addressed the practitioner who reduced the invention to practice, but did not stick to any precise theoretical values. Varying results did not, therefore, necessarily prevent a person skilled in the art from carrying out an invention (Art. 83 EPC 1973), but could be a matter of the definition of the invention under Art. 84 EPC 1973. See also T 960/98, where the board stated that the relevant question with respect to sufficiency of disclosure was whether the patent in suit provided sufficient information to enable the skilled person, taking into account common general knowledge, to reproduce the invention, and T 586/94, T 245/98 and T 859/06.

Following T 378/97, the board in T 439/98 found that the appellant's objections in regard to sufficiency of disclosure (the patent in suit allegedly failed to indicate a suitable method for measuring porosity), concerned the scope of the value of porosity indicated in the claim and therefore the clarity of the claim, rather than the possibility of reproducing the invention. In T 619/00, the board agreed that the different methods for determining the value of the gel fraction did not per se represent an undue burden. In the absence of evidence that the different methods specified would lead to determination values deviating from each other by a substantial amount having technical significance (following T 378/97), or by an amount that would place the skilled person in a situation where he was unable to carry out the invention (following T 930/99), the mere fact that the patent specification was silent as to which method should be used did not prejudice sufficiency of disclosure. The question whether the methods defined lead to a unique value or to different values also concerned the clarity of the definition of the subject-matter of the claim under Art. 84 EPC 1973. In T 930/99 only one measuring method was involved and the board had therefore considered T 225/93 inapplicable, (according to T 225/93, different measuring methods which did not always lead to the same result could amount to an undue burden). The respondent's argument that there would be legal uncertainty, since third parties would not know whether they were working within or outside the range specified, was clearly an argument based on lack of clarity, which was not a ground of opposition and so could not be considered. See also T 396/02, T 347/10.

In T 805/93 the viscosity was the only characterizing feature of the claim at issue and its role in defining the matter for which protection was sought under Art. 84 EPC, was clearly crucial. The lack of information on how the viscosity limit of the claim was to be determined meant the matter for which protection was sought could not be deemed defined, so that the claim did not comply with Art. 84 EPC 1973. In addition, the disclosure of the application in suit did not enable him to carry out the claimed subject-matter on a general basis, so that the requirements of Art. 83 EPC 1973 were also not met. Similarly, in T 431/07, since no method to measure the viscosity was mentioned in the description and due to the numerous methods and devices used to measure viscosity, the information available in the description as originally filed was not sufficient for the person skilled in the art to reproduce the claimed subject-matter under Art. 83 EPC.

T 482/09 concerned the viscosity of a substance, a common parameter for which standard measurement methods were undisputedly known. The appellants' argument was instead that the parameter's value was uncertain because different measurement methods led to different results. According to the board, however, using an indefinite term in the claims was not a problem under Art. 83 EPC, but rather under Art. 84 EPC (see also T 1886/06), which requires, among other things, that the claims define the matter for which protection is sought. The appellants had cited one of the criteria for sufficient disclosure set out in T 256/87, namely that a skilled person reading the patent specification should 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, but the board held that this criterion could not be taken to mean that an invention was inevitably unworkable under Art. 83 EPC wherever the claims used a term which was vague for the purposes of Art. 84 EPC and could not be defined more precisely on the basis of the description or common general knowledge. In opposition and any ensuing appeal proceedings, the result of using such an indefinite term in a claim was instead that it could not be taken to determine the limits to the protection sought, so that novelty and inventive step had to be assessed in the light of the prior art identified on the basis of all its technically meaningful possible interpretations. If the term had no specific meaning whatsoever, it would even lose entirely its effect of delimiting the claimed subject-matter from the relevant prior art.

See also T 2001/12, which dealt with the distinction between the requirements of sufficiency of disclosure (Art. 83 EPC), clarity of the claims (Art. 84 EPC) and inventive step (Art. 56 EPC). T 862/11 dealt with this distinction in detail too.