From the same idea of regularity and conjunction arise all the schemes of policy in consequence of which men propose to themselves, by a certain plan of conduct, to prevail upon others to become the tools and instruments of their purposes. All the arts of courtship and flattery, of playing upon men's hopes and fears, proceed upon the supposition, that mind is subject to certain laws, and that, provided we be skilful and assiduous enough in applying the motive, the action will envitably follow.
Lastly, the idea of moral discipline proceeds entirely upon this principle.
If I carefully persuade, exhort, and exhibit motives to another, it is because I believe that motives have a tendency to influence his conduct.
If I reward or punish him, either with a view to his own improvement, or as an example to others, it is because I have been led to believe that rewards and punishments are calculated to affect the dispositions and practices of mankind.
There is but one conceivable objection against the inference from these premises to the necessity of human actions. It may be alleged that "though there is a real coherence between motives and actions, yet this coherence may not amount to a certainty, and of consequence, the mind still retains an inherent activity, by which it can at pleasure supersede and dissolve it. Thus for example, when I address argument and persuasion to my neighbour, to induce him to adopt a certain species of conduct, I do it not with a certain expectation of success, and am not utterly disappointed if my efforts fail of their object. I make a reserve for a certain faculty of liberty he is supposed to possess, which may at last counteract the best digested projects."