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2.24 Possession of the common general knowledge in the art is one of the most significant aspects of the hypothetical person skilled in the art. To a large extent this can be said to be what characterises the person skilled in the art. In a purposive construction it is this knowledge that the person skilled in the art uses to construe the specification, and it is with such a background and context that the person skilled in the art reads the prior art
2.25 A good description of common general knowledge was given by Laddie J in Bourns Inc v Raychem Corp  RPC 31:
“The common general knowledge is the technical background of the notional [skilled person]… This is not limited to material he has memorised and has at the front of his mind. It includes all that material in the field he is working in which he knows exists, which he would refer to as a matter of course if he cannot remember it and which he understands is generally regarded as sufficiently reliable to use as a foundation for further work or to help him understand the pleaded prior art.”
2.26 It is important to distinguish common general knowledge from public knowledge – just because something is in the public domain does not make it part of the common general knowledge. As Laddie J also explained:
“This does not mean that everything on the shelf which is capable of being referred to without difficulty is common general knowledge nor does it mean that every word in a common text book is either.”
2.27 However he went on to say that it may be assumed in most cases that standard textbooks or readily available trade literature may be considered common general knowledge in the art.
2.28 Sachs LJ (General Tire & Rubber Co v Firestone Tyre & Rubber Co Ltd  RPC 457) noted that patent documents would not normally be considered common general knowledge, but if a particular patent is well known or one that skilled persons in a particular industry would routinely consider, this may not be the case:
“The two classes of documents which call for consideration in relation to common general knowledge in the instant case were individual patent specifications and ‘widely read publications’.
As to the former, it is clear that individual patent specifications and their contents do not normally form part of the relevant common general knowledge, though there may be specifications which are so well known amongst those versed in the art that upon evidence of that state of affairs they form part of such knowledge, and also there may occasionally be particular industries (such as that of colour photography) in which the evidence may show that all specifications form part of the relevant knowledge.”
2.29 In the case of scientific papers, he referred to Luxmoore J in British Acoustic Films  53 RPC 221:
“In my judgment it is not sufficient to prove common general knowledge that a particular disclosure is made in an article, or series of articles, in a scientific journal, no matter how wide the circulation of that journal may be, in the absence of any evidence that the disclosure is accepted generally by those who are engaged in the art to which the disclosure relates. A piece of particular knowledge as disclosed in a scientific paper does not become common general knowledge merely because it is widely read, and still less because it is widely circulated. Such a piece of knowledge only becomes general knowledge when it is generally known and accepted without question by the bulk of those who are engaged in the particular art; in other words, when it becomes part of their common stock of knowledge relating to the art.
… It is certainly difficult to appreciate how the use of something which has in fact never been used in a particular art can ever be held to be common general knowledge in the art.” [emphasis added]
2.30 The choice of person skilled in the art will depend on the nature of the technology. In some cases this may mean that the common general knowledge in the field is possessed by relatively few people. For example, in Apimed Medical Honey Ltd v Brightwake Ltd  RPC 16, the invention related to surgical dressings comprising honey and a gelling agent. The Court determined that even though there were few people having the knowledge of treating wounds with honey, this still formed part of the common general knowledge in that field.
2.31 However, even if a matter may be well-known to a few, it is not considered part of the common general knowledge unless it can be shown to be known to and accepted by the large majority of those skilled in the art. In Beloit v Valmet (No.2)  RPC 489 Aldous L J stated that:
“It has never been easy to differentiate between common general knowledge and that which is known by some. It has become particularly difficult with the modern ability to circulate and retrieve information. Employees of some companies, with the use of libraries and patent departments, will become aware of information soon after it is published in a whole variety of documents; whereas others, without such advantages, may never do so until that information is accepted generally and put into practice. The notional skilled addressee is the ordinary man who may not have the advantages that some employees of large companies may have. The information in a patent specification is addressed to such a man and must contain sufficient details for him to understand and apply the invention. It will only lack an inventive step if it is obvious to such a man.
It follows that providing evidence that a fact is known or even well-known to a witness does not establish that the fact forms part of the common general knowledge. Neither does it follow that it will form part of the common general knowledge if it is recorded in a document.”
2.32 In most cases an assertion that certain information forms part of common general knowledge should be supported by documentary evidence. As noted above a description in standard textbooks may provide a strong indication of being the common general knowledge. It may also be assumed that a scientific paper that is widely cited has entered into the common general knowledge. A set of industry standards may be considered to be part of the common general knowledge. It is not expected that the person skilled in the art would know the information, but rather that he would know where to find the relevant information (Nokia v Ipcom  EWHC 3482). In other cases, an Examiner may assert that a document is common general knowledge based on evidence ascertained (for example, that the document has been published in a widely-read or respected publication, or where patents would form part of the common stock of knowledge of persons skilled in that technology). However evidence to the contrary from the applicant may be sufficient to overcome such an assertion.