[Footnote 21 Were morality discoverable by reason, and not by sentiment, it would 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 coud 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 should 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.  It is impossible, therefore, we cou’d ever will a new obligation; and consequently it is impossible the will cou’d ever accompany a promise, or produce a new obligation of morality.]

But, secondly, if there was any act of the mind belonging to it, it could not naturally produce any obligation.  This appears evidently from the foregoing reasoning.  A promise creates a new obligation.  A new obligation supposes new sentiments to arise.  The will never creates new sentiments.  There could not naturally, therefore, arise any obligation from a promise, even supposing the mind could fall into the absurdity of willing that obligation.

The same truth may be proved still more evidently by that reasoning, which proved justice in general to be an artificial virtue.  No action can be required of us as our duty, unless there be implanted in human nature some actuating passion or motive, capable of producing the action.  This motive cannot be the sense of duty.  A sense of duty supposes an antecedent obligation:  And where an action is not required by any natural passion, it cannot be required by any natural obligation; since it may be omitted without proving any defect or imperfection in the mind and temper, and consequently without any vice.  Now it is evident we have no motive leading us to the performance of promises, distinct from a sense of duty.  If we thought, that promises had no moral obligation, we never should feel any inclination to observe them.  This is not the case with the