If determinism is true, then, where p is any true proposition ascribing an action to some human agent, p is logically implied by any conjunction consisting of a proposition that expresses the laws of nature and a proposition that describes the state of the universe at some time prior to the origin of human existence. Now it is not within our power to change the past, nor is it within our power to change the laws of nature. Further, if the truth of p follows logically from propositions describing things that one is unable to change, then it is not within one's power to make p false. Hence, if determinism is true, then, where p is any true proposition ascribing an action to some human agent, it is not within anyone's power to make p false. That is to say, if determinism is true, then it is not within anyone's power to perform any actions other than the ones that he or she actually does perform.