…absence of evidence is not evidence of absence.
Carl Sagan, The Demon-Haunted World, First Edition, Random House, New York, 1995, at p. 213
The absence of an apparent motive to fabricate an allegation against an accused is a neutral factor when assessing the credibility of a complainant. As Trotter, J. states, speaking for a unanimous Court of Appeal R. v. Bartholomew,  O.J. No. 2371, beginning at para 22:
…it is dangerous and impermissible to move from an apparent lack of motive to the conclusion that the complainant must be telling the truth. People may accuse others of committing a crime for reasons that may never be known…
… there is a "significant difference" between absence of proved motive and proved absence of motive… (citations omitted)
As Trotter, J. confirms at para. 25:
…an absence of evidence of a proved motive…..was not capable of enhancing the complainant's credibility, as the trial judge did. At best, it was a neutral factor.
There is no onus on the defence to establish a motive for the complainant to fabricate an allegation, but where such evidence exists, it may detract from the complainant’s credibility. As Trotter, J., states in Bartholomew, supra, at para. 21:
An ulterior motive, or a motive to fabricate, on the part of a complainant may be … important. From the defence perspective, proof of such a motive provides a compelling alternative to the truth of the allegations.