  Reid's idea is that the only conception we can have of the exertion of power is of that distinctive sort of mental effort in which we engage when we will to do something. Since he holds that the power to act is always accompanied with the power to exert that power, it follows that the only entities that can have power are those who are capable of engaging in the peculiar sort of mental effort with which we are all familiar from our own case. But then it follows that the only entities that can have power are those with minds. When coupled with the claim, that Reid also makes, that every event is efficiently caused, it follows that every event in nature is directed towards an end; everything that happens is chosen to occur. In fact, Reid holds that all and only our free actions are those events of which we are the efficient causes. An agent who has the power to bring about a particular action is said, by Reid, to have ‘moral liberty’.