Art. 54(2) EPC 1973 did not limit the state of the art to written disclosure in specific documents. Rather it defined it as including all other ways ("in any other way") by which technical subject-matter could be made available to the public. Therefore, the absence of a reference to a particular document did not mean that there was no state of the art, as this could reside solely in the relevant common general knowledge, which, again, might be in writing, i.e. in textbooks or the like, or be simply a part of the unwritten "mental furniture" of the notional "person skilled in the art" (T 939/92, OJ 1996, 309).
In the case of any dispute as to the extent of the relevant common general knowledge this, like any other fact under contention, had to be proved, for instance by documentary or oral evidence (T 1242/04, OJ 2007, 421; T 537/90, T 329/04 and T 811/06).
In T 666/89 (OJ 1993, 495) the board noted that the decision depended on the facts of each case. It found that, provided the information in the prior art document, in combination with the skilled person's common general knowledge, was sufficient to enable him to practise the technical teaching, and if it could reasonably be assumed that he would do so, then the claim in question would lack novelty.
In T 1641/11 the board stated that according to the established case law of the boards of appeal, common general knowledge was represented by basic handbooks and textbooks on the subject in question; it did not normally include patent literature and scientific articles (see T 766/91 and T 20/81, OJ 1982, 217).
In T 766/91 the board stated that by its very nature common general knowledge could be inferred from a number of sources, and proof that something was general knowledge in a particular art did not depend on proof of any particular document being published at a particular date, so that, for example, for the purposes of R. 55(c) EPC 1973, it would be sufficient to state a fact and allege that it was general knowledge in the art concerned, without referring to a particular publication. Substantiation of an allegation that something was common general knowledge was only required if this was challenged by another party or the EPO. Publication in an encyclopaedia or basic textbook could usually be accepted as evidence not merely that the information was known, but that it was common general knowledge.
In T 412/09 the board stated that the case law contemplates exceptions to the general rule and allows in particular circumstances allows the establishment of common general knowledge on the basis of the content of patent specifications (see T 890/02 below). This is so in particular when a series of patent specifications provides a consistent picture that a particular technical procedure was generally known and belonged to the common general knowledge in the art at the relevant date.
In T 890/02 (OJ 2005, 497) the board stated that the common general knowledge of the person skilled in the art had been defined by the boards of appeal as being normally represented by encyclopaedias, textbooks, dictionaries and handbooks on the subject in question (see inter alia T 766/91, T 206/83, OJ 1987, 5; T 234/93). In several cases, however, and by way of exception, patent specifications and scientific publications had also been considered to form part of common general knowledge. In particular, special considerations prevailed when a field of research was so new that technical knowledge was not yet available from textbooks (see T 51/87 OJ 1991, 177; T 772/89).
Further, it was noted that boards had acknowledged that the skilled person did not necessarily have knowledge of the whole technology and identified three important aspects - common to all cases - for correctly assessing the common general knowledge of skilled persons. First, the skills of such a person included not only having basic general knowledge of the particular prior art, but also knowing where to find such information, be it in a collection of relevant studies (see T 676/94), a scientific publication or a patent specification (see T 51/87 and T 772/89). Second, it could not be expected that, in order to identify this common general knowledge, the skilled person would carry out a comprehensive search of the literature covering virtually the whole state of the art. No undue effort in the way of such a search could be required of the skilled person (see T 171/84, OJ 1986, 95; T 206/83; T 676/94). Third, the information found had to be unambiguous and usable in a direct and straightforward manner without doubts or further investigation (see T 206/83). These three aspects actually corresponded to the classic steps of (a) picking the right reference book (handbook, encyclopaedia, etc.) from the bookshelf in the library, (b) looking at the appropriate entry without any significant effort, and (c) getting the correct information or unambiguous data that could be used without further investigation. It followed that for each case the common general knowledge of the skilled person working in a particular technical field had to be decided on its own merits, based on the facts and evidence of the case. In the case at issue, the board found that the EMBL/GenBank databases were not common general knowledge in the sense defined in the case law.
In T 206/83 (OJ 1987, 5) it was held that information which could only be obtained after a comprehensive search was not to be regarded as part of the common general knowledge.
In T 786/00 the board stated that, according to established case law, when considering the question of novelty, a prior art document must be interpreted in the light of common general knowledge available at its publication date. Common general knowledge which did not exist at this date, but which only became available at a later date, could not be used to interpret such a document (cf. T 229/90, T 965/92).
In T 1110/03 (OJ 2005, 302), the board stated that when evaluating evidence relating to the issues of novelty and inventive step it was necessary to distinguish between a document alleged to be part of the state of the art within the meaning of Art. 54(2) EPC 1973 - in the sense that the document itself was alleged to represent an instance of what had been made available to the public before the priority date of the opposed patent - and a document which was not itself part of the state of the art, but which was submitted as evidence of the state of the art or in substantiation of any other allegation of fact relevant to issues of novelty and inventive step. In the first situation, the document was direct evidence of the state of the art; its status as state of the art could not normally be challenged except on authenticity. In the second situation, the document was also evidence, albeit indirect; it provided a basis for an inference about e.g. the state of the art, common general knowledge in the art, issues of interpretation or technical prejudice, etc. - an inference which was subject to challenge as to its plausibility. Only a document of the first kind could be disregarded on the sole ground that it was post-published; documents of the second kind did not stand or fall by their publication date even on issues of novelty and inventive step (T 23/02, T 1625/06, T 608/07).