 Metaphysical philosophers do not mean by “agent” only the principle of motion, as the natural philosophers mean, but the principle and giver of existence, as in the case of God with respect to the world. As for the natural efficient cause, it does not bestow any existence other than motion in one of the forms of motion. Thus, in the natural sciences, that which bestows existence is a principle of motion. (Avicenna MH: 195, trans. modified)