The same level of skill has to be applied when, for the same invention, the two questions of sufficient disclosure and inventive step have to be considered (T 60/89, OJ 1992, 268; T 373/94). T 694/92 (OJ 1997, 408) added that, although the same level of skill is applied for both Art. 56 and Art. 83 EPC 1973, the two starting points differ; for inventive step purposes, the skilled man knows only the prior art; for sufficiency of disclosure, he knows the prior art and the disclosed invention.

According to T 426/88 (OJ 1992, 427) a book providing general teaching in a general technical field covering the invention's specific technical field was part of the general knowledge of a specialist in that specific technical field. When books, representing common general knowledge, described a basic general technical theory or methodology and exemplified the same with specific applications in certain technical fields only, these did not limit the general scope and relevance of such disclosures so as to exclude possible applications in other fields. The appellant had argued that the book, written in German, was not a general reference book consulted by experts in that field in Great Britain. The board, however, adhered to the definition of the state of the art given in Art. 54 EPC 1973, according to which no account was taken of the location at which the skilled person exercised his profession.

In T 1688/08 the board stated that the language of a patent document alone cannot be decisive for the question of whether or not the skilled person considers the technical content of that document. Otherwise, there would be a differentiation between skilled persons according to the language(s) they speak. This would be against the objective assessment of the inventive step.

In T 766/91 the board summarised the normally accepted view that common general knowledge was represented by basic handbooks and textbooks on the subject in question. It was knowledge that an experienced person in this field was expected to have, or at least to be aware of, to the extent that he knew he could look it up in a handbook if he needed it. Statements in such works were used as convenient references to show what was common knowledge. The information as such did not as a rule become such knowledge through publication in a given handbook or textbook; rather by the time it appeared in such works it was already generally known. For this reason, publication in an encyclopaedia, say, could normally be taken as proof that the information was not only known but was common general knowledge. The assertion that something was part of the common general knowledge therefore needed only to be substantiated if challenged by another party or the EPO (T 234/93, T 590/94, T 671/94, T 438/97, T 1253/04, T 1641/11). Where an assertion that something was part of the common general knowledge is challenged, the person making the assertion must provide proof that the alleged subject-matter indeed forms part of the common general knowledge (T 438/97, T 329/04, T 941/04, T 690/06).

In T 378/93 the board confirmed this case law, adding that the same applied to articles in scientific periodicals addressed primarily to qualified professionals and enjoying worldwide repute.

In T 1540/14 the board held that the common general knowledge of the skilled person is not normally established on the basis of the content of patent documents.

In T 939/92 (OJ 1996, 309) it was explained that the state of the art could also perfectly well reside solely in the relevant common general knowledge, which, in turn, need not necessarily be in writing, i.e. in textbooks or the like, but might simply be a part of the unwritten "mental furniture" of the average skilled person. In the case of any dispute, however, the extent of the relevant common general knowledge had to be proven, e.g. by documentary or oral evidence.

Numerous publications in the specialist press over a fairly short time, reporting on meetings and research in a particularly active field of technology, could reflect common general knowledge in this field at that time (T 537/90).

In T 632/91 the board stated that evidence which did not comprise a comparison of the claimed subject-matter with the state of the art might nevertheless rebut a prima facie assumption that there existed some common general knowledge which would have allowed the skilled person to disregard structural differences in chemical compounds.