Thomas Aquinas, who lived before the Humean restrictions about "is" and "ought," dared to go beyond the abstract principle, "Do good and avoid evil," to point out three specific "oughts" derived from the tendencies and appetites of human nature itself. (This triad of precepts is not original with Aquinas, but appears in Cicero, the Roman jurists, Aquinas's scholastic predecessors and successors, and even as late as the 18th century in Montesquieu.)
The most important precept is indeed, as contemporary ethicists often maintain, to act rationally. But for Aquinas, rationality is not just about avoiding self-contradiction; he points out two specific and necessary manifestations of rationality: 1) in the theoretical realm, always pursue the truth; and 2) in the practical realm, contribute to communal and societal harmony. A second precept, experienced by humans as well as animals, is to procreate and care for offspring; humans, of course, require an extraordinarily long period of nurturing. And the third precept is what is called in common parlance the "law of self-preservation."
Well, what does that imply?These natural laws are also rights. The duty of seeking the truth implies the right to the truth, and certainly involves a right to necessary information and education; the duty of contributing to communal harmony implies the right to work towards that end -- a right with political implications; the duty of caring for one's offspring (Aquinas would consider this the main argument against abortion, not the general "right to life") implies the right to reproduce (not the bizarre modern inversion of "reproductive rights"); and the duty of self-preservation implies the right of self-preservation (implying the right to the wherewithal necessary for maintaining physical life).
Kainz also discusses Grizes, Finnis, Hume, and a new Lutheran manifesto on ethics.