In T 688/91 the board found that the fact that claims of different categories were deemed to be independent claims did not preclude reference to other independent claims. In the board's view, however, any such reference had to make perfectly clear whether or not the reference was intended to replace features. In the former case, it had for reasons of clarity to replace all the features, and in the latter case none.

In case T 410/96 concerning a data processing system the question arose whether it was permissible for a claim to a system to refer back to a claim to a method. The board held that, although R. 29(4) EPC 1973 mentioned a reference only in the context of a claim including all the features of the claim it referred to, this did not imply a contrario that a reference which did not fulfil this condition was necessarily impermissible. The board found that there was no a priori objection under Art. 84 EPC 1973 to an independent claim which partially drew its features from preceding claims of a different category. The essential features were thus incorporated in the disputed claim by reference, the claim thus complying with R. 29(3) EPC 1973 (R. 43(3) EPC).

In T 1722/11 a claim related to a computer program resident on computer-readable media was defined by reference to a method claim. The execution of the method required co-ordinated interaction between various resources in a communication network. As these resources were at different, mutually remote locations, the board considered it unclear how the method referred to could be executed solely by a (single) computer program when run on a computer. The claim thus lacked clarity.

In decisions T 418/92 and T 453/90 the boards confirmed that it was possible for claims to relate to both physical activities and physical entities, in particular where the inventions concerned were fully disclosed as processes to the skilled person only if apparatus features were also included in the definition. In T 1046/05 too the board confirmed the clarity of an apparatus feature in a process claim.

In T 426/89 (OJ 1992, 172) the board decided that a claim relating to a "method for operating" a device was not "clear" (Art. 84 EPC 1973) if the claimed features only described how the device worked.

In T 841/95 the board found that where a claim for an apparatus sought to define the invention by reference to features of the use to which the apparatus was to be put, a lack of clarity could result. However, if the subject-matter of the application was an apparatus and it was not viable to define the apparatus other than by reference to the said use, an apparatus claim directed to a combination of apparatus and use and defining the apparatus unambiguously could be clear.

Including in a device claim "for carrying out a process" a reference back to an earlier claim did not alter the fact that it was an independent (non-process) claim; rather, it limited the claimed device to being suitable to carry out the process referred to (T 1017/98).

A claim in T 952/99 contained two different aspects of a use claim: on the one hand it defined the use of a particular physical entity to achieve an 'effect', and on the other it defined its use to produce a product. Although a use claim normally falls into either one category or the other, the board found that such a clear distinction was not possible in this case. The claim contained both application and process features and there was a technical affinity between the additional process step and the 'core' of the invention. Both the application and process features were thus technical features of the invention, so that their combination did not contravene R. 29(1) EPC 1973, the relevant criterion for assessing the extent to which the combination of a 'use' claim and technical process features was allowable from the point of view of clarity. The board drew a distinction with T 796/91, in which it had been held that the heterogeneous combination of process features and application features rendered the claim fundamentally unclear. That case had concerned the combination of a process claim and a use claim with no process claim at all. In contrast to the case before the board, the process features had apparently had no affinity to the application features, which had made it impossible to subsume the two different types of technical feature under one claim.

In T 921/11 the board considered that the claims as a whole, construed in the light of the description, were so unclear as to the meaning of the term "system" that the skilled reader was neither in a position to recognise the nature of the claimed subject-matter nor the category to which claim 1 belonged.

For the particularities of product-by-process claims, see in this chapter II.A.7.