 In a short essay on the mind’s capacity to form a design, Shepherd confronts the question how, if at all, the mind can cause motion in the body: how can a state of a conscious being—that of conceiving a design and willing to implement it—determine the motion of the body to this end? (Essay XIII, EPEU: 403–05). She explains that when a person forms a plan and decides to carry it out, the conscious state is united with whatever bodily qualities co-exist with it. The union begins a bodily motion directed to an end by the mind. The bodily part of the union is the cause of the beginning of motion; it is necessary that this cause be similar to whatever impulse causes other motions. Since we are not conscious of the cause, but only the design and volition, it is impossible for us to know its nature. Yet in this respect, the cause of voluntary motion is no more mysterious than any other cause. We are acquainted with the effects the living body has on our consciousness, but have no knowledge of its nature unperceived. 