Those who affirm that virtue is nothing but a conformity to reason; that there are eternal fitnesses and unfitnesses of things, which are the same to every rational being that considers them; that the immutable measures of right and wrong impose an obligation, not only on human creatures, but also on the Deity himself: all these systems concur in the opinion, that morality, like truth, is discerned merely by ideas, and by their juxtaposition and comparison. In order, therefore, to judge of these systems, we need only consider, whether it be possible, from reason alone, to distinguish betwixt moral good and evil, or whether there must concur some other principles to enable us to make that distinction. If morality had naturally no influence on human passions and actions, 'twere in vain to take such pains to inculcate it; and nothing would be more fruitless than that multitude of rules and precepts with which all moralists abound. Philosophy is commonly divided into _speculative_ and _practical_; and as morality is always comprehended under the latter division, 'tis supposed to influence our passions and actions, and to go beyond the calm and indolent judgments of the understanding. And this is confirmed by common experience, which informs us, that men are often governed by their duties, and are deterred from some actions by the opinion of injustice, and impelled to others by that of obligation. Since morals, therefore, have an influence on the actions and affections, it follows, that they cannot be derived from reason; and that because reason alone, as we have already proved, can never have any such influence. Morals excite passions, and produce or prevent actions. Reason of itself is utterly impotent in this particular. The rules of morality, therefore, are not conclusions of our reason. No one, I believe, will deny the justness of this inference; nor is there any other means of evading it, than by denying that principle, on which it is founded. As long as it is allowed, that reason has no influence on our passions and actions, 'tis in vain to pretend that morality is discovered only by a deduction of reason. An active principle can never be founded on an inactive; and it reason be inactive in itself, it must remain so in all its shapes and appearances, whether it exerts itself in natural or moral subjects, whether it considers the powers of external bodies, or the actions of rational beings. It would be tedious to repeat all the arguments, by which I have proved,[1] that reason is perfectly inert, and can never either prevent or produce any action or affection. 'Twill be easy to recollect what has been said upon that subject. I shall only recall on this occasion one of these arguments, which I shall endeavour to render still more conclusive, and more applicable to the present subject.