Many decisions of the boards of appeal warn against an ex post facto approach when assessing inventive step (see also the Guidelines G-VII, 8 – June 2012 version). This applies especially to inventions which at first sight seem obvious, to combination inventions and where the proposed solution is supposedly "simple". Correct application of the problem and solution approach avoids this inadmissible ex post facto analysis which draws on knowledge of the invention (T 24/81, OJ 1983, 133; T 564/89, T 645/92, T 795/93).
When assessing inventive step, an interpretation of the prior art documents as influenced by the problem solved by the invention, where the problem was neither mentioned or even suggested in those documents, must be avoided, such an approach being merely the result of an a posteriori analysis (T 5/81, OJ 1982, 249; T 63/97, T 170/97, T 414/98).
In T 970/00 the board stated that any ex post facto analysis, and in particular any conclusion going beyond what the skilled person would have objectively inferred from the prior art, without the benefit of hindsight knowledge of the invention, is of necessity at variance with a proper application of the problem-solution approach. Any attempt to interpret the disclosure of the closest prior art so as to distort or misrepresent, based on hindsight knowledge of the invention, the proper technical teaching of the disclosure in such a way that it artificially meets specific features recited in the claim under consideration must fail, especially as this would risk unfairly and tendentiously concealing the technical contribution of the invention and prejudice the subsequent objective determination of the technical problem solved by the claimed invention (see also T 266/07).