Plan of Discussion: Focus on First Criterion

If the argument of Chapter 4 has been successful, then it is apparent that in the Groundwork, from the Preface all the way up to the statement of the Formula of Universal Law in Section II, Kant develops criteria that the supreme principle of morality must fulfill. According to his basic concept, already implicit in the Preface, this principle must be practical, absolutely necessary, binding on all rational agents, and serve as the supreme norm for the moral evaluation of action (section I.2). Later in the Groundwork Kant develops four additional criteria (Chapter 4). The supreme principle of morality must be such that: (1) all and only actions conforming to this principle because the principle requires it – that is, all and only actions done from duty – have moral worth; (2) the moral worth of conforming to this principle from duty stems from its motive, not from its effects; (3) an agent's representing this principle as a law, that is, a universally and unconditionally binding principle, gives him sufficient incentive to conform to it; (4) a plausible set of duties (relative to ordinary rational knowledge of morals) can be derived from this principle.

Until Chapter 8, I have little more to say about the fourth criterion. Kant appeals to ordinary rational knowledge of morals in developing criteria 1–3.