 As mentioned above, traditional theists believe that God is immutable (cannot change) and impassible (cannot be affected by anything external). These ideas are related to one another, but not identical: if God is immutable, then God is impassible. But just because God is impassible, it does not follow that God is immutable—God might be able to change without being affected by any external source. If God is both immutable and impassible, then it seems that no petitionary prayers are effective. 