"Falsus in uno falsus in omnibus" applies only if witness willfully lies on a few material points

It is perfectly within the discretion of the trial court to accept portions of the testimony of a witness as it may deem credible and reject those which it believes to be false. The maxim falsus in uno falsus in omnibus is not an absolute rule of law and is in fact rarely applied in modern jurisprudence. For this maxim to be invoked, the witness must first be shown to have willfully falsified the truth on one or more material points. But even so when he is found to have willfully falsified this does not make his entire testimony totally incredible. The court may still, upon its discretion, admit and credit those portions worthy of belief depending upon the corroborative evidence and the probabilities as well as improbabilities of the case. [G.R. No. 115217. November 21, 1996]