39 The question as to the capability of the evidence to rationally affect the assessment of the probability of the existence of a fact in issue is to be determined by a trial judge on the assumption that the jury will accept the evidence. This follows from the words “if it were accepted”, which are expressed to qualify the assessment of the relevance of the evidence. This assumption necessarily denies to the trial judge any consideration as to whether the evidence is credible. Nor will it be necessary for a trial judge to determine whether the evidence is reliable, because the only question is whether it has the capability, rationally, to affect findings of fact. There may of course be a limiting case in which the evidence is so inherently incredible, fanciful or preposterous that it could not be accepted by a rational jury. In such a case its effect on the probability of the existence of a fact in issue would be nil and it would not meet the criterion of relevance.
42 Both s 97(1)(b) and s 137 require an assessment of the probative value of the evidence tendered. As mentioned, the Dictionary definition of the “probative value” of evidence describes evidence which is probative in the same terms as how relevant evidence is described in s 55, namely evidence which “could rationally affect […] the assessment of the probability of the existence of a fact in issue”.
43 The enquiry for the purposes of s 55 is whether the evidence is capable of the effect described at all. The enquiry for the purposes of determining the probative value of evidence is as to the extent of that possible effect. But the point is that in both cases the enquiry is essentially the same; it is as to how the evidence might affect findings of fact. An assessment of the extent of the probative value of the evidence takes that enquiry further, but it remains an enquiry as to the probative nature of the evidence.