His great disciple, Dr. Priestley, pursues precisely the same course. “If a man,” says he, “be wholly a material being, and the power of thinking the result of a certain organization of the brain, does it not follow that all his functions must be regulated by the laws of mechanism, and that of consequence his actions proceed from an irresistible necessity?” And again, he observes, “the doctrine of necessity is the immediate result of the materiality of man, for mechanism is the undoubted consequence of materialism.”(18) Priestley, however, allows us to possess free-will as defined by Hobbes, Locke, and Hartley. Helvetius himself could easily admit such a liberty into his unmitigated scheme of necessity, but he did not commit the blunder of Locke and Hartley, in supposing that it bore on the great question concerning the freedom of the mind. “It is true,” he says, “we can form a tolerably distinct idea of the word _liberty_, understood in its common sense. _A man is free who is neither loaded with irons nor confined in prison_, nor intimidated like the slave with the dread of chastisement: in this sense the liberty of man consists in the free exercise of his power; I say, of his power, because it would be ridiculous to mistake for a want of liberty the incapacity we are under to pierce the clouds like the eagle, to live under the water like the whale, or to become king, emperor, or pope. We have so far a sufficiently clear idea of the word. But this is no longer the case when we come to apply liberty to the will. What must this liberty then mean? We can only understand by it a free power of willing or not willing a thing: but this power would imply that there may be a will without motives, and consequently an effect without a cause. A philosophical treatise on _the liberty of the will_ would be a treatise of effects without a cause.”(19)