As advocated by St. Anselm, God is a maximally perfect being. If ignorance is an imperfection, all things being equal [according to Ockham’s razor], then it is greater to be knowledgeable. To prevent initial detractions from the classical definition of omniscience, omniscience should be understood as knowing all truths.
O. For any agent x, x is omniscient= def. For every statement s, if s is true, then x knows that s and does not believe that not-s.
If there are truths about future contingents, God, as an omniscient being must know these truths. Since there are truths about the future, that is to say, since statements about future contingents are either true or false, and they are not all false, God must therefore know all truths about the future, which is to say He knows future-tense facts; He knows what will happen. One may try to avoid this reasoning by contending that future-tense statements are neither true nor false, so that there are no facts about the future. Since the future does not exist, it is claimed that the respective future-tense statements cannot be true or false, simply without truth. To make this assertion is a misunderstanding behind the statement’s truth claim. For a future tense-statement to be true it is not required that what it describes exist, but that it will exist. In order for a future-tense statement to be true, all that is required is that when the moment described arrives, the present-tense version of the statement will be true at that moment. Nicholas Rescher gives an illustration for this assertion: