When preparing to cross-examine a witness, counsel must keep in mind the distinction between honesty and accuracy.
The criminal justice system demands honest communication from witnesses. Witnesses are compelled, under threat of criminal penalty, to tell the truth, the whole truth and nothing but the truth. A witness for the prosecution who displays an intention to mislead the Court during cross-examination may be fatal to the state's case.
Counsel may also demonstrate during cross-examination that the evidence of a witness is unsound for reasons that have nothing to do with the sincerity of the witness. Testimonial evidence may be compromised by limitations in a witness's powers of observation, recollection, and/or communication.
The criminal practitioner is well aware that testimony from an honest, but inaccurate witness, has the potential to lead to a miscarriage of justice. For example, developments in forensic science have led to the exoneration of individuals who were honestly, but mistakenly, identified as the perpetrator.
Counsel will be well served to revisit Justice Doherty’s helpful discussion of the distinction between truthfulness and accuracy in R. v. Morrissey,  O.J. 639 (C.A.) at para. 33:
Testimonial evidence can raise veracity and accuracy concerns. The former relate to the witness's sincerity, that is, his or her willingness to speak the truth as the witness believes it to be. The latter concerns relate to the actual accuracy of the witness's testimony. ....When one is concerned with a witness's veracity, one speaks of the witness's credibility. When one is concerned with the accuracy of a witness's testimony, one speaks of the reliability of that testimony….
Sam Harris’s philosophical essay, Lying, 2013, Four Elephants Press, also addresses this conceptual distinction at page 4:
…To speak truthfully is to accurately represent one’s beliefs. But candor offers no assurance that one’s beliefs about the world are true.