According to the established case law of the boards of appeal Art. 84 EPC has to be interpreted as meaning not only that a claim must be comprehensible from a technical point of view, but also that it must define the object of the invention clearly, that is to say indicate all the essential features thereof. An independent claim should explicitly specify all essential features needed to define the invention (G 1/04, OJ 2006, 334). All features which are necessary for solving the technical problem with which the application is concerned have to be regarded as essential features; see on this issue T 32/82 (OJ 1984, 354) and T 115/83, confirmed inter alia in T 269/87, T 409/91 (OJ 1994, 653), T 694/92 (OJ 1997, 408), T 1055/92 (OJ 1995, 214), T 61/94, T 488/96, T 203/98, T 260/01, T 813/03, T 1540/12, T 2427/13, T 1180/14, T 30/16. The indication of all essential features is seen as necessary to meeting the clarity requirement.

The board's opinion in T 32/82 was also confirmed in T 622/90, where it was held that lack of clarity could be caused not only by the presence of an ambiguous feature, but also by the absence of a feature which was necessary for clarity. See also T 630/93.

The essential features should in particular comprise those which distinguish the invention from the prior art (T 1055/92, OJ 1995, 214; T 813/03). Regarding the delimitation of essential from non-essential features, see also T 61/94, T 203/98, T 141/00, T 260/01, T 1573/12, T 2131/12.

According to the board in T 888/07, if from the wording of an independent claim it must be concluded that a solution of the problem of the invention is achieved by not needing a step, whereas this very feature according to the description cannot be abolished, but is necessary for a workable solution, then such a features is to be considered an essential feature of the invention. An independent claim missing this feature is therefore neither clear, nor supported by the description. See also in this chapter II.A.5.

In T 809/12 the board stated that, if an independent claim contained a feature defined by a result to be achieved which essentially corresponded to the problem underlying the application, to comply with Art. 84 EPC 1973 the remaining features of the claim had to comprise all essential features necessary for achieving that result. See also T 2427/13.

According to the board in T 818/03 a method claim which does not state sufficiently clearly the steps by which a particular result was achieved might still be considered clear provided the result to be achieved was clearly defined. A claim which defines a method of achieving some less than clearly defined result might also still be considered clear provided the steps that need to be taken to achieve that result are sufficiently clearly defined. However, a claim must be considered to lack clarity if, as here, it sets out insufficiently clearly both the necessary parameters of the method and the relevant characteristic features of the result.

In T 409/91 the invention related to fuel oils. In the description the use of certain additives was presented as an essential constituent of the fuel oil composition. As this feature was missing in the claims, the board found that they defined some other invention which was not sufficiently disclosed. Although the requirements of sufficient disclosure of the invention (Art. 83 EPC) and support by the description (Art. 84 EPC) were related to different parts of the patent application, they gave effect to the same legal principle that the extent of a patent monopoly, as defined by the claims, should correspond to the technical contribution to the art (see also chapter II.C.8. "The relationship between Article 83 EPC and Article 84 EPC"). In T 30/16 the board held that the technical contribution of an invention did not lie in the fact that the problem was solved, but rather in the combination of features by which it was solved.

In T 2001/12 the board held that, if doubt that the invention as claimed is capable of solving the problem defined in the application arises because the claim fails to specify those features which are disclosed in the application as providing the solution to the problem, then the description and claims are inconsistent in relation to the definition of the invention, and an objection under Art. 84 EPC 1973 may properly arise that the claims do not contain all the essential features necessary to specify the invention (see also chapter II.C.6. "Reproducibility"). See also T 1180/14.

In T 1055/92 the board stated that since the primary function of a claim was to set out the scope of protection sought for an invention, it was not always necessary for a claim to identify technical features or steps in detail. This primary function of the claims should be clearly distinguished from the requirement that the European patent application had to disclose the invention in such a way that it enabled a person skilled in the art to carry out that same invention. Under Art. 83 EPC 1973 sufficient disclosure was required of a European patent application but not of an individual claim as such. A claim had to comprise the essential features of the invention; the essential features should in particular comprise those features which distinguished the invention from the closest prior art. See also T 61/94.

In T 914/02 the appellant sought to derive from the alleged sheer complexity of the proposed solution an implied use of technical means, in particular a computer. According to the board, it was doubtful as a matter of principle whether complexity could be used to disqualify an activity as a mental activity (see also chapter I.A.1.4.2 "Technical considerations and technical implementations"). Rather, it would appear generally that if computer means were indeed indispensable, they should be included in the claim as an essential feature of the invention.

G 1/04 (OJ 2006, 334) concerned diagnostic methods. The Enlarged Board held that a diagnostic method within the meaning of Art. 52(4) EPC 1973 had an inherent and inescapable multi-step nature. If diagnosis as the deductive medical or veterinary decision phase was a purely intellectual exercise, the feature pertaining to the diagnosis for curative purposes and the features relating to the preceding steps which were constitutive for making the diagnosis represented the essential features of a diagnostic method within the meaning of Art. 52(4) EPC 1973. Thus, in order to satisfy the requirements of Art. 84 EPC 1973, an independent claim relating to such a method must include these features. The Enlarged Board further held that, while essential features were for the most part of a technical nature, a non-technical feature constitutive for defining the invention must likewise be included as an essential feature in the independent claim. Thus, although diagnosis stricto sensu was a purely intellectual exercise unless it was carried out by a device, the feature pertaining to it was such an essential feature as to be included in the independent claim. See also chapter I.B.4.5.1 d) "Clarity of a claim relating to diagnostic methods".

G 1/07 (OJ 2011, 134) concerned surgical methods. The Enlarged Board referred to G 1/04 and stated that a claim should explicitly specify all essential features and must be clear. Under Art. 84 EPC, whether or not a step being or encompassing a surgical step excluded from patentability can be omitted either by using positive wording for such omission like "pre-delivered" or by simply leaving it out from the claim depends on whether the claimed invention is fully and completely defined by the features of the claim without that step. See also chapter I.B.4.3.4 b) "Surgical step part of claimed method?".

In T 2102/12 the application related to medical robotic systems which allow to robotically move a tool on an articulated arm in response to the surgeon's manipulation of an input device. The board referred to G 1/07 and held that claiming the measurement of the movement of the tool while "unclaiming" the movement itself rendered the claim unclear under Art. 84 EPC. The claimed method of intertwined non-surgical ("claimed") and surgical ("unclaimed") steps was not comparable to that underlying T 836/08.

In decision T 923/08 the board decided as follows: If a method for recording measurements on the human or animal body necessarily entails a surgical step in order to fix to the human or animal body a measuring device which is indispensable for performing the method, this step has to be deemed an essential feature of the method and is comprised in such a method, even if the claim contains no method feature explicitly directed to it. Such a method is excluded from patentability under Art. 53(c) EPC. The exclusion of such a surgical step, whether by stating that the surgically attached measuring device was already fixed to the body before the start of the method or whether by use of a disclaimer, breaches Art. 84 EPC 1973 because such a process claim does not then include all the essential features of the claimed invention.