It would not be obvious to a skilled person to combine an isolated, very old document (i.e. 50 year old document), which had not given rise to a trend in the art and whose teaching ran counter to the present trend, with the document reflecting the closest state of the art (T 261/87, T 366/89, T 404/90).
In T 745/92 the board pointed out that the disclosure of two prior documents - even if they were classified under the same IPC classification - could only be combined so as to result in a finding of lack of inventive step if such combination would have been obvious to a skilled person seeking to solve the problem underlying the claimed invention (T 104/95, T 395/00).
In T 715/09 the respondent submitted that the skilled person versed in the art of glow plugs would not, as part of his common knowledge, be aware of plasma deposition technology. Support for this submission was that glow plugs and surface treatment techniques were in two completely different classes according to the international patent classification scheme. The board disagreed and stated that IPC classification alone was no reason for determining whether or not two pieces of prior art could be combined. The mere fact that two documents had the same classification was no reason for saying the combination of the teachings was obvious (T 745/92). Likewise the mere fact that the technologies had been given different IPC classes did not necessarily mean that they could not be combined.
In T 552/89 the board confirmed that, when assessing inventive step, it was not permissible to combine the teachings of different documents within the state of the art in order to establish the obviousness of a claimed invention, unless it would have been obvious for the skilled person to do so at the time of filing. When a problem defined by reference to the closest prior art as disclosed in a primary document consisted of individual problems, board of appeal case law stated that the skilled person could be expected to take account of solutions to the individual problems proposed in different secondary documents in the same or neighbouring technical fields. Thus, the teachings of secondary documents might be combined with the disclosure of the closest prior art if such secondary documents provided solutions to specific individual problems forming part of the objective problem in progressing from the closest prior art, in particular when such individual solutions were merely aggregated together in the claimed invention (see also T 302/02, T 881/09).
In T 302/02 the board added that, if an invention consisted of a new combination of features taken from different technical areas, a discussion whether or not it was obvious would normally involve at least as many documents as technical areas combined in it. The board adopted the approach taken in T 552/89, according to which a technical problem might be formed of "individual problems". The number of individual problems obviously depended on the degree of detail of the claim under consideration and the cited decision did not suggest that beyond a certain number the presence of an inventive step might be taken for granted. On the contrary, it was said to be obvious to try to solve the individual problems as long as the corresponding solutions were "merely aggregated together" in the claim.
In T 881/09 the board stated that since the teachings of both documents stood in heavy discrepancy to each other, in view of their incompatibilities a combination of these documents was not obvious (T 552/89) but rather artificial and could only be the result of an ex post facto analysis.