Lewis, like Reichenbach a probabilist at heart, insisted that the assessment and revision of probabilities in the light of experience requires that some propositions obtained from experience be certain, or as he put it, "if anything is probable, something must be certain".
Thus, if a RI is purchased and utilised for fewer than R ̂ months, then there is no longer a cost saving; in fact, the RI will be more expensive than the on-demand price, P D. For this reason, to guarantee savings on a RI purchase, one must be certain that it will be utilised for at least R ̂ months of the full R-months term.
That is to say, j must be certain for the subject before it can make anything else certain.
Collectors and investors must be certain that an artwork is genuine, and they must know what it is worth to be able to protect it against loss.
But however he justified it, Philo's new conception of knowledge challenged the fundamental epistemological principle of the Hellenistic period that knowledge must be certain.
Investors from abroad must be certain that there is an atmosphere of mutual respect and understanding.
Doctors must be certain the vibrations caused by the radio frequencies will not harm that artery.
