The person of ordinary skill in the art is assumed to posses some common general knowledge in the field of the invention.¹ The skilled person is also “thought to be reasonably diligent in keeping up with advances in the field to which the patent relates” and their common knowledge “undergoes continuous evolution and growth”.² The determination of whether a particular piece of information has become common general knowledge may be critical to the determination of obviousness, since it is clear that something within the common general knowledge of a skilled person cannot be “inventive”.

Not everything that has been published before the relevant date is included in the common general knowledge. There is a distinction made between “public knowledge” (i.e. everything that has been made public before the relevant date) and “common general knowledge” (which includes only information that can be found by a “reasonably diligent search”).³ Public knowledge only becomes common general knowledge “when it is generally regarded as a good basis for further action by the bulk of those who are engaged in the particular art”.⁴ The distinction may be important in some cases, because whereas prior public disclosures can be used to attack a patent for anticipation, it cannot be used for the purpose of obviousness unless it was part of the common general knowledge.

Harold G. Fox put it this way:⁵

A piece of particular information 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 information only becomes common knowledge when it is generally known and accepted without question by the bulk of those engaged in the particular art, in other words, when it becomes part of the common stock of ideas relating to the art. Common knowledge does not include public knowledge of particular documents⁶ but rather the knowledge that a fully fledged practitioner in an art may be expected to have as part of his technical equipment ⁷.

Despite the foregoing, there have been warnings from courts that the distinction between public knowledge and common general knowledge may become moot in light of increasingly powerful information technologies.⁸

See also: expert evidence.

To prove common general knowledge, it is often necessary to adduce expert evidence. Due to the importance of common general knowledge in some cases, however, courts may often encounter conflicting evidence as to what was within the skilled person's knowledge. This is especially difficult since common general knowledge can include things that are not written down.⁹

• Patent specifications (and by extension published patent applications) do not necessarily form a part of the common general knowledge. They must be well known to a skilled person to form part of such knowledge. This may in some cases depend on the industry.¹⁰
• Scientific papers are not automatically considered a part of the common general knowledge, even if they are widely read and circulated. Such 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.¹¹
• Posters from academic conferences are not part of the common general knowledge merely because they were displayed publicly, especially if there was no way of locating them by a reasonably diligent search.¹²
• “Standard” textbooks may be a part of common general knowledge, but probably not textbooks that are particularly specialized and not readily available to a skilled person.¹³