According to the principle of free evaluation of evidence, each piece of evidence is given an appropriate weighting according to its probative value. As the Enlarged Board of Appeal pointed out in G 3/97 (OJ 1999, 245, point 5 of the Reasons) and G 4/97 (OJ 1999, 270, point 5 of the Reasons), "(t)he principle of free evaluation would be contradicted by laying down firm rules of evidence defining the extent to which certain types of evidence were, or were not, convincing" (cited in G 1/12, OJ 2014, A114).

The following cases illustrate how the boards have evaluated various pieces of evidence in the light of the specific circumstances.