In later times, it was often objected that incorporeal volitions cannot move the corporeal pineal gland because this would violate the law of the conservation of energy. Descartes did not have this problem because he did not know this law. He may nevertheless have foreseen difficulties because, when he stated his third law of motion, he left the possibility open that it does not apply in this case: “All the particular causes of the changes which bodies undergo are covered by this third law—or at least the law covers all changes which are themselves corporeal. I am not here inquiring into the existence or nature of any power to move bodies which may be possessed by human minds, or the minds of angels” (AT VIII:65, CSM I:242).