This research is divided into two sections. In the first section a deep analysis of the theory of natural law designed by Germain Grisez and John Finnis, known as New Natural Law Theory, is developed, while the second section underlines some criticisms to the thesis supported by the two authors. More in details, the first section highlights the features of the New Classical Theory: on the one hand the elements belonging to the Thomistic tradition, on the other those belonging the (...) analytic area. Moreover the most important theoretical elements of this new philosophical theory are analyzed: the basic goods and the basic requirements of practical reasonableness. The basic goods are essential to build an integral human fulfillment. Instead, the basic requirements of practical reasonableness assess the action criteria, while respecting the natural law. Finally the section includes an highlight on the practical reason and the first principle of morality: “In voluntarily acting for human goods and avoiding what is opposed to them, one ought to choose and otherwise will those and only those possibilities whose willing is compatible with a will toward integral human fulfillment”. The second part of the first section examines in details the laws defined and established by the Governament. The following topics are covered: the Rule of Law, the qualities of a good law, the relationship between human law and natural law, the unjust laws, the link between public authority and people consensus, the principles of justice and freedom, the interaction immoral acts and punishment (main argument of the book “Making Men Moral” by Robert P. George). Within this second section, the Thomistic thesis is used to arise some criticism to the Finnis and Grisez’s ideas, being the main focus on: the foundation of natural law (metaphysics for Aquinas, empirical for Grisez and Finnis), the rejection of the ultimate end, the dynamic of moral action, the pre-morality of the basic goods, basic requirements of practical reasonableness, first principle of practical reason, the moral relevance of intention in actions, the principles of autonomy and self-determination. In the second half the lex humana, according to The Aquinas, is analysed and details are given as far as the purpose and nature of ius positivum, the human law content and validity as it is given by the natural law, the weaknesses of both laws (lex naturalis and lex humana), with the goal of making a comprehensive comparisons between the two. The research deals also with the concept of “common good”, as the set of conditions that is useful to live virtuously and the set of values that produces social cohesion. Finally the complex issue of unjust laws and “imperfect” laws are discussed. (shrink)