When it is said that the mind cannot be caused to act, President Day must have known in what sense the term cause is used in this proposition. He must have known, that no one meant to assert, that there are no _conditions_ or _antecedents_, on which the action of the mind depends. There is not an advocate of free-agency in the universe, who will contend, that the mind can choose a thing, unless there is a thing to be chosen; or, to take his own illustration, can read a book, unless there is a book to be read. The question is not, whether there are _conditions_, without the existence of which the mind cannot act; this no one denies; but whether there is, or can be, a real and efficient cause of the mind's action. The point in dispute, relates not to mere fact of dependence, but to the _nature_ of that dependence. The question is, _can the mind be efficiently caused to act?_ This being the question, what does it signify to tell us, that it cannot read a book, unless it has a book to read? Or what does it signify to tell us, that a body may be caused to move? These are mere irrelevancies; they fall short of the point in dispute; and they only seem to reach it by means of a very "convenient ambiguity" of words. But still it may be said, that although a body is passive in motion, it may act upon other bodies, and thereby communicate motion to them. This is the ground taken by President Day. "The very same thing," says he, "may be both cause and effect. The mountain wave, which is the effect of the wind, may be the cause which buries the ship in the ocean," p. 160. I am aware, that one body is frequently said to _act_ upon another; but this word action, as President Day has well said, is a term "of very convenient ambiguity, with which it is easy to construct a plausible but fallacious argument," p. 159. The only cause in every case of motion, is that _force_, whatever it may be, which acts upon the body moved, and puts it in motion. All the rest is pure passion or passiveness. The motion of the body is not action; it is the most pure passion of which the mind can form a conception. If a body in action is said to act upon another, this is but a metaphor; there is no real action in the case. Indeed, if a body be put in motion, and meets with no resistance, it will move on in a right line forever--and why? just because of its _inertia_, of its inherent destitution of a power to act. As a mathematician, President Day certainly knew all this; but he seems to have forgotten it all, in his eagerness to support the cause of moral necessity.