Natural law is an attempt to delineate the duties that are universal to every human being. Rights and duties are mirror images. For example, the right of a woman to her own body implies the duty of all others not to aggress against her. It is not a synonym for legislation. Although rights and duties are not categories of fact, they are far more than mere conventions upon which human beings have agreed.
Human values derive directly from reality and human nature.
Thus, some actions can be said to be naturally right or naturally wrong. In this sense, we should scarcely say that the rules of good surgical practice are mere agreed-upon conventions with no natural basis at all. Surely, it would be odd if they were the only human skills that were arbitrary. Therefore, a natural right involves behaviours that one ought or should adopt in order to achieve well-being. This is the sense in which values or ethics accompany the doctrine of natural law.