There is another class of theologians, of whom Edwards is one, who endeavour to escape the difficulties which attend a total inability, by making the distinction of moral and natural inability:--man, they say, is morally unable to do good, and naturally able to do good, and therefore he can justly be made the subject of command, appeal, rebuke, and exhortation. The futility of this distinction I cannot but think has already been made apparent. It may be well, however, inasmuch as so great stress is laid upon it, to call up a brief consideration of it in this particular connexion. Moral inability, as we have seen, is the impossibility of a given volition, because there are no motives or causes to produce it. It is simply the impossibility of an effect for the want of a cause: when we speak of moral cause and effect, according to Edwards, we speak of nothing different from physical cause and effect, except in the quality of the terms--the relation of the terms is the same. The impossibility of a given volition, therefore, when the appropriate motive is wanting, is equal to the impossibility of freezing water in the sun of a summer's noon-tide.[1] When objects of volition are fairly presented, an inability to choose them must lie in the state of the mind, sensitivity, desire, will, or affections, for all these have the same meaning according to this system. There is no volition of preference where there is no motive to this effect; and there is no motive to this effect where the state of the mind is not in correlation with the objects presented: on the contrary, the volition which now takes place, is a volition of refusal. Natural inability, as defined by this system, lies in the connexion between the volition considered as an antecedent, and the effect required. Thus I am naturally unable to walk, when, although I make the volition, my limbs, through weakness or disease, do not obey. Any defect in the powers or instrumentalities dependent for activity upon volition, or any impediment which volition cannot surmount, constitutes natural inability.[2] According to this system, I am not held responsible for anything which, through natural inability, cannot be accomplished, although the volition is made. But now let us suppose that there is no defect in the powers or instrumentalities dependent for activity upon volition, and no impediment which volition cannot surmount, so that there need be only a volition in order to have the effect, and then the natural ability is complete:--I will to walk, and I walk. Now it is affirmed that a man is fairly responsible for the doing of anything, and can be fairly urged to do it when all that is necessary for the doing of it is a volition although there may be a moral inability to the volition itself.