One solution to this is modal logic, where you have the modifiers "necessary" (written "[]" or as a box) and "possible" (written "<>" or as a diamond). So instead of "a sea-battle will be fought tomorrow", which is neither true nor false, you can only express "it is necessary that a sea battle be fought tomorrow" (which is false, you cannot know the future) or "it is possible that a sea battle be fought tomorrow" (which is true, unless it is impossible, in which case it is false).
