He answers these questions precisely as they were answered by Luther and Calvin more than a hundred years before his time. In order to solve this great difficulty, and establish an agreement between necessity and liberty, he insists on the distinction between co-action and necessity. Sir James Mackintosh says, that “in his treatise _de Servo Arbitrio_ against Erasmus, Luther states the distinction between co-action and necessity as familiar a hundred and fifty years before it was proposed by Hobbes, or condemned in the Jansenists.”(10) According to his definition of liberty, it is merely a freedom from co-action, or external compulsion. “I conceive liberty,” says he, “to be rightly defined in this manner: Liberty is the absence of all the impediments to action that are not contained in the nature and intrinsical qualities of the agent: as for example, the water is said to descend freely, or to have liberty to descend by the channel of the river, because there is no impediment that way; but not across, because the banks are impediments; and though the water cannot ascend, yet men never say it wants liberty to ascend, but the faculty or power, because the impediment is in the nature of the water and intrinsical.” According to this definition, though a man’s volitions were thrown out, not by himself, but by some irresistible power working within his mind, say the power of the Almighty, yet he would be free, provided there were no impediments to prevent the external effects of his volitions. This is the liberty which water, impelled by the power of gravity, possesses in descending the channel of a river. It is the liberty of the winds and waves of the sea, which, by a sort of metaphor, is supposed to reign over the dominions of a mechanical and materialistic fate. It is the most idle of all idle things to speak of such a liberty, _or rather, to use the word in such a sense_, when the controversy relates to the freedom of the mind itself. What has such a thing to do with the origin of human volitions, or the nature of moral agency? Is there no difference between the motion of the body and the action of mind? Or is there nothing in the universe of God but mere body and local motion? If there is not, then, indeed, we neither have nor can conceive any higher liberty than that which the philosopher is pleased to allow us to possess; but if there be mind, then there may be things in heaven and earth which are not dreamed of in his philosophy.