T 3.2.5.4 n77

Were morality discoverable by reason, and not by sentiment, 'twou'd be still more evident, that promises cou'd make no alteration upon it. Morality is suppos'd to consist in relation. Every new imposition of morality, therefore, must arise from some new relation of objects; and consequently the will cou'd not produce immediately any change in morals, but cou'd have that effect only by producing a change upon the objects. But as the moral obligation of a promise is the pure effect of the will, without the least change in any part of the universe; it follows, that promises have no natural obligation. Shou'd it be said, that this act of the will being in effect a new object, produces new relations and new duties; I wou'd answer, that this is a pure sophism, which may be detected by a very moderate share of accuracy and exactness. To will a new |obligation, is to will a new relation of objects; and therefore, if this new relation of objects were form'd by the volition itself, we shou'd in effect will the volition; which is plainly absurd and impossible. The will has here no object to which it cou'd tend; but must return upon itself in infinitum. The new obligation depends upon new relations. The new relations depend upon a new volition. The new volition has for object a new obligation, and consequently new relations, and consequently a new volition; which volition again has in view a new obligation, relation and volition, without any termination. 'Tis impossible, therefore, we cou'd ever will a new obligation; and consequently 'tis impossible the will cou'd ever accompany a promise, or produce a new obligation of morality.