Two landmark decisions, T 176/84 (OJ 1986, 50) and T 195/84 (OJ 1986, 121) addressed in detail the problem of the relevant technical field, i.e. the question of the extent to which neighbouring areas beyond the specific field of the application might be taken into consideration when assessing inventive step. According to T 176/84, when examining for inventive step, a skilled person would, as well as considering the state of the art in the specific technical field of the application, look for suggestions in neighbouring fields or a broader general technical field if the same or similar problems arose, and if he could be expected to be aware of such general fields. T 195/84 added that the state of the art also had to include prior art in a non-specific (general) field dealing with the solution of any general technical problem which the application solved in its specific field. Such solutions of general technical problems in non-specific (general) fields had to be viewed as forming part of the general technical knowledge which a priori was to be attributed to those skilled persons versed in any specific technical field. These principles were applied in a large number of decisions.
In T 560/89 (OJ 1992, 725) the board took the view that the skilled person would also draw on prior art in other fields which were neither neighbouring nor broader general fields, if prompted to do so because the materials used were related or because of public debate about a technical problem common to both fields. Expanding on this, T 955/90 added that, in practice, the person skilled in a broader general field would also draw on the narrower, more specialised field of the known main application of the general technology in search of a solution to a problem lying outside the special application of that technology (T 379/96).
According to T 454/87 a skilled person specialising in a particular technical field (gas chromatography equipment) would, in the course of his normal professional activity, also observe developments in equipment used in a related technical field (absorption spectral analysis).
In T 891/91 the board stated that a skilled person in the field of lenses for ophthalmic use, confronted with the technical problem of adhesion and abrasion resistance of a coating made on a surface of the lens, would also refer to the state of the art in the more general field of coated plastic sheets in which the same problems of adhesion and abrasion resistance of the coating arose and of which he was aware.
According to the board in T 1910/11, whether the prior art and the claimed invention belonged to neighbouring technical fields within the meaning of T 176/84 was less a question of whether the relevant implementation parameters were identical than a question of the degree of similarity between the respective problems, boundary conditions and functional concepts. Applying this to the case in hand, it observed that automotive electronics and avionics were traditionally considered to be neighbouring technical fields because they involved similar problems (e.g. interference resistance, robustness and reliability), boundary conditions (e.g. mobility) and functional concepts (e.g. physical/logical separation of the communications systems for safety and maintenance data in the vehicle).
In T 767/89, regarding carpets, the board ruled that wigs were neither a neighbouring technical field nor a broader general one which included the former field. So wigs were not a related technical field in which the person skilled in carpets would have been prompted to seek solutions. The two inventions addressed different problems; the user requirements were not comparable.
Because of the differing security risks, a skilled person could not be expected to search in the field of bulk-goods packaging for ideas for the design of a closure for a means of conveying money (T 675/92).
Further comments on the concept of relevant field are to be found in several other decisions, including the following: T 277/90 (in dentistry, moulding technology and prosthodontics are neighbouring technical fields), T 358/90 (discharging the content of a portable toilet did not lead the skilled person to the field of filling a tank of a chain saw by means of a special kind of container), T 1037/92 (a person skilled in the art of making fuse links for programmable ROMs would also have consulted the documentation in the field of ultraminiaturised integrated switches), T 838/95 (the pharmaceutical and cosmetic fields were immediate neighbours), T 26/98 (the board did not consider the field of electrochemical generators to be a neighbouring field of iontophoresis because, though both fields relied on electrochemical processes, such processes had substantially different purposes and applications and, consequently, had to satisfy different requirements), T 1202/02 (the manufacture of mineral fibres and that of glass fibres were two closely related technical fields irrespective of differences between the raw materials respectively used), T 365/87, T 443/90, T 47/91, T 244/91, T 189/92, T 861/00.
On a different aspect, with regard to the applicant's reference to a remote state of the art, the board gave the following ruling in T 28/87 (OJ 1989, 383); if reference is made in the introduction to the description of an application or a patent to a state of the art which cannot objectively be classified as a relevant field, that state of the art cannot in the course of examination for patentability be applied to the applicant's or patent proprietor's disadvantage as a neighbouring field merely on account of that reference.