The first question that confronts the doctrine of natural law is: how can social norms be ascertained from the Is of human nature? This question raises the preliminary problem as to whether there is a constant human nature at all, a secondary issue which has to be decided before the answer to the main question can be sought.
"Two Arguments for an Empirical Foundation of Natural-Law Norms: An Examination of Johannes Messner's and Victor Kraft's Approaches,"
Syracuse Journal of International Law and Commerce:
1, Article 13.
Available at: http://surface.syr.edu/jilc/vol3/iss1/13