He proceeds to develop this conception of a Will in itself good and estimable, by dealing with the commonly received ideas of Duty.  Leaving aside profitable actions that are plain violations of duty, and also actions conformed to duty, but, while not prompted directly by nature, done from some special inclination—­in which case it is easy to distinguish whether the action is done from duty or from self-interest; he considers those more difficult cases where the same action is at once duty, and prompted by direct natural inclination.  In all such, whether it be duty of self-preservation, of benevolence, of securing one’s own happiness (this last a duty, because discontent and the pressure of care may easily lead to the transgression of other duties), he lays it down that the action is not allowed to have true moral value, unless done in the abeyance or absence of the natural inclination prompting to it.  A second position is, that the moral value of an action done from duty lies not in the intention of it, but in the maxim that determines it; not in the object, but in the principle of Volition.  That is to say, in action done out of regard to duty, the will must be determined by its formal a priori principle, not being determined by any material a posteriori motive.  A third position follows then from the other two; Duty is the necessity of an action out of respect for Law.  Towards an object there may be inclination, and this inclination may be matter for approval or liking; but it is Law only—­the ground and not the effect of Volition, bearing down inclination rather than serving it—­that can inspire Respect.  When inclination and motives are both excluded, nothing remains to determine Will, except Law objectively; and, subjectively, pure respect for a law of practice—­i.e., the maxim to follow such a law, even at the sacrifice of every inclination.  The conception of Law-in-itself alone determining the will, is, then, the surpassing good that is called moral, which exists already in a man before his action has any result.  Conformity to Law in general, all special motive to follow any single law being excluded, remains as the one principle of Volition:  I am never to act otherwise, than so as to be able also to wish that my maxim (i.e., my subjective principle of volition) should become a universal law.  This is what he finds implied in the common notions of Duty.

Having illustrated at length this reading, in regard to the duty of keeping a promise, he contrasts, at the close of the section, the all but infallibility of common human reason in practice with its helplessness in speculation.  Notwithstanding, it finds itself unable to settle the contending claims of Reason and Inclination, and so is driven to devise a practical philosophy, owing to the rise of a ‘Natural Dialectic’ or tendency to refine upon the strict laws of duty in order to make them more pleasant.  But, as in the speculative region, the Dialectic cannot be properly got rid of without a complete Critique of Reason.