For the understanding gives us no inkling a priori that a cause is possible which alters the state of things,.e., determines them to the opposite of a certain given state, not merely because it simply does not give us insight into the possibility of this (for this insight is lacking in many a priori cognitions), but rather because alterability concerns only certain determinations of appearances, about which experience alone can teach us, while their cause is to be found in the unalterable.