Finnis on Hume's Dictum, etc.

"The substantive differences between the theory of natural law espoused by Vasquez and Suarez (and most Catholic manuals until the other day) and the theory espoused by Aquinas are scarcely less significant and extensive than the better-known differences between Aristotelian and Stoic ethics. . . .We can put Hume's attack on the ethics of his predecessors into perspective by the following summary remarks:(i)Aristotle and Aquinas would readily grant that ought cannot be deduced from is (whether or not Hume really formulated and adhered to that principle).  (ii)Both would go along with Hume's view that the speculative discernment of "eternal relations," even relations of "fitness of human nature," leaves open the question what motive anybody has for regulating his actions accordingly.  (iii) Aquinas would deplore the confusion (shared by Hume and Suarez!) of obligation with impulse or influence, and Hume's failure to see that reason is an "active principle" because one is motivated according to one's understanding of the goodness and desirability of human opportunities, including the opportunity of extending intelligence and reasonableness into one's choice of actions.  (iv)Aquinas would reject the assumption of Clarke, Grotius, Suarez, and Vasquez that the primary and self-evident principles of natural law are moral principles (in the modern sense of "moral"), or that they are initially grasped as principles concerned  with self-evident relations of conformity or dis-conformity to human nature.  (v)Aquinas, like Clarke and Hume, would reject the view that the will or imperative of a superior accounts for obligation;  like Hume he would reject Clarke's view that obligation is essentially a matter of avoiding intellectual inconsistencies;  and finally he would reject both Hume's view that it is a matter of, or intrinsically related to, a peculiar sentiment, and equally, the recent neo-Humean view that statements of obligation are merely prescriptions expressing a certain sort of commitment or decision."  John Finnis, Natural Law and Natural Rights, II.6, p47-48