Rationalism:... universally valid, absolute, and immutable principles of human conduct

[28] The central characteristic of the modern natural law tradition (as represented by St. Thomas Aquinas, Luis de Molina, Francisco Suarez, and the late sixteenth century Spanish Scholastics, and the Protestant Hugo Grotius) was its thorough rationalism: its idea of universally valid, absolute, and immutable principles of human conduct that are — ultimately independent of any theological beliefs — to be discovered by and founded in and reason alone.

"Man," writes Frederick C. Copleston, [Aquinas (London: Penguin Books, 1955), pp. 213–14]

cannot read, as it were, the mind of God … (but) he can discern the fundamental tendencies and needs of his nature, and by reflecting on them he can come to a knowledge of the natural moral law…. Every man possesses … the light of reason whereby he can reflect … and promulgate to himself the natural law, which is the totality of the universal precepts of dictates of right reason concerning the good which is to be pursued and the evil which is to be shunned.

On the origin and development of the natural rights doctrine and its idea of justice and property (including all the statist failings and slips of its aforementioned heroes) see Richard Tuck, Natural Rights Theories (Cambridge: Cambridge University Press, 1979); on the revolutionary character of the idea of natural law see Lord (John) Acton, Essays on Freedom and Power (Glencoe, Ill.: Free Press. 1948); as an eminent contemporary natural rights philosopher see Henry Veatch, Human Rights (Baton Rouge: Louisiana State University Press, 1985)." The Sociology of Taxation by Hans-Hermann Hoppe