An anticipation is accidental if it is so unrelated to and remote from the claimed invention that the person skilled in the art would never have taken it into consideration when making the invention. When an anticipation is taken as accidental, this means that it appears from the outset that the anticipation has nothing to do with the invention (G 1/03 and G 2/03, OJ 2004, 413 and 448; T 134/01, T 1911/08).
In G 1/03 and G 2/03 (OJ 2004, 413 and 448), the Enlarged Board of Appeal observed that different definitions of accidental anticipation had been put forward (see referrals T 507/99 and T 451/99). Often cited were decisions T 608/96 and T 1071/97, which said in similar terms that a disclosure was accidentally novelty-destroying if it was disregarded by the skilled person faced with the problem underlying the application, either because it belonged to a remote technical field or because its subject-matter suggested it would not help to solve the problem. Thus, according to these decisions, the disclosure had to be completely irrelevant for assessing inventive step.
The Enlarged Board noted that the individual elements of these and other attempts to find an adequate definition could not be taken in isolation. The fact that the technical field was remote or non-related might be important but was not decisive because there were situations in which the skilled person would also consult documents in a remote field. Even less decisive, as an isolated element, was the lack of a common problem, since the more advanced a technology was, the more the problem might be formulated specifically for an invention in the field. Indeed, one and the same product might have to fulfil many requirements in order to have balanced properties making it an industrially interesting product. Correspondingly, many problems related to different properties of the product might be defined for its further development. When looking specifically at improving one property, the person skilled in the art could not ignore other well-known requirements. Therefore, a "different problem" might not yet be a problem in a different technical field. What counted was that from a technical point of view, the disclosure in question had to be so unrelated and remote that the person skilled in the art would never have taken it into consideration when working on the invention (to this effect, see T 608/96, cited in referral T 507/99). This should be ascertained without looking at the available further state of the art because a related document did not become an accidental anticipation merely because there were other disclosures which were even more closely related. In particular, the fact that a document was not considered to be the closest prior art was not sufficient to accept an accidental anticipation (see, however, T 170/87, OJ 1989, 441).
Accidental anticipation understood in the sense outlined above not only corresponds to the literal meaning of the term, but also limits disclaimers to situations in which there is a justification comparable to the case of conflicting applications for which the allowability of disclaimers has been accepted (see also Chapter II.E.1.4 "Disclaimers").
In T 161/82 (OJ 1984, 551) the board found that the prior art document was concerned with the solution of a problem totally different from that stated in the application at issue and concluded that in cases where an anticipation was of a chance nature, in that what was disclosed in a prior document could accidentally fall within the wording of a claim to be examined for novelty without there being a common technical problem, a particularly careful comparison had to be made between what could fairly be considered to fall within the wording of the claim and what was effectively shown in the document (see also T 986/91).