10.8.1 General

An effect which may be said to be unexpected can be regarded as an indication of inventive step (T 181/82, OJ 1984, 401). However, certain preconditions have to be met.

If, having regard to the state of the art, it would already have been obvious for a skilled person to arrive at something falling within the terms of a claim, because an advantageous effect could be expected to result from the combination of the teachings of the prior art documents, such claim lacked inventive step, irrespective of the circumstance that an extra effect (possibly unforeseen) was obtained (T 21/81, OJ 1983, 15; see also T 365/86, T 350/87, T 226/88, T 1317/13, T 696/19, T 1491/20). Similarly, where, because of an essential part of the technical problem being addressed, the state of the art obliged a skilled person to adopt a certain solution, that solution was not automatically rendered inventive by the fact that it also unexpectedly solved part of the problem (T 69/83, OJ 1984, 357; see also T 231/97).

According to the case law of the boards of appeal, an improvement is not a prerequisite for inventive step (see also in this chapter I.D.4.5 "Alternative solution to a known problem"). Likewise, the achievement of a surprising effect is no precondition for the existence of inventive step. All that is necessary is to ascertain that the respective subject-matter could not be derived by the skilled person in an obvious manner from the available prior art (T 154/87; see also T 426/92, T 164/94, T 960/95, T 524/97, T 888/08).

For an additional, unexpected effect to be disqualified as a mere bonus effect, it has to be shown either that the situation was characterised by a lack of alternatives as regards the means for achieving the first, expected improvement (the "one-way-street" situation explained in T 192/82), or that, considering the relative technical and practical importance of the effects in the circumstances of the case, the additional unexpected effect was merely accidental (following T 227/89). See also T 1356/21.