The Palmer principles prohibiting invitation to speculate on absence of motive to lie apply equally to prosecutor's closing addresses as to cross-examination. Where a prosecutor invites speculation about why a complainant would fabricate allegations of sexual assault, and there is no evidentiary base for the motive question, a specific corrective direction is required — a general warning against speculation is insufficient. However, there is a distinction between commenting on the absence of a particular person's motive to lie (impermissible) and commenting on objective measures for testing the probabilities of a complainant's account (permissible), though the boundary between these categories is contested.
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