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St. Thomas Aquinas Lecture, Introduction to Philosophy, 2002

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Thomas Aquinas and the Natural Law

St. Thomas Aquinas (1225- 7th March, 1274), the Angelic Doctor, the Prince of the Scholastics, corpulent and silent, he was called the dumb ox in his day. He wrote (among many other works) the Commentary on the Sentences (1253-7), the Summa contra Gentiles (1261-4), and the Summa Theologiae I and II (1266-71) and III (1272) which was left unfinished at his death.

He followed an invariable sequence of objection, solution, and argument of the medieval disputation, without registering a difference between the most trivial insights and most supreme truths. But an architecture arises out of his systematic thought comparable to the cathedral of Salisbury.[1]

Crucial teachings of St. Thomas:

Reality is rational and the rational is real.

What is natural is rational and what is rational is natural.

Grace does not destroy nature but perfects it.

William F. Lawhead provides a helpful diagram for Thomas Aquinas’ Natural Theology, his truths known by faith, his comparison by analogy for God versus his Natural Philosophy and the truths known by reason for the concerns of the world:


Thomas Aquinas Diagram

Aquinas, in his great synthesis is trying to join the empirical and natural tendencies of Aristotle with the Neo-Platonic, the very transcendental other-worldly tendency Christian Theology had entered. Aquinas also argued that not man, but the Divine Intellect is measure of all things and all human inclinations should be governed by reason. “Wherefore, since the rational soul is the proper form of [human beings], there is in [everyone] a natural inclination to act according to reason: and this is to act according to virtue.”[2]

In his introduction to his reprint from Summa Theologiae, entitled St. Thomas Aquinas: Treatise on Law, Stanley Parry, writes the three laws – eternal, natural and human – are not three independent rules of action, but one rule progressively specified.[3] Like Aristotle, Thomas was able to categorize laws as if they were biological. First the definition: law is a rule or measure of human acts; law is the director of human acts.

Natural law is a participation in the eternal law.

What do you make of my almost biological classifying of law?

Kingdom: ———- Divine Law

———-phylum:  ———– eternal law

———-class: ————— natural law –

———-order: ————— human law –

———-family: —————canon law or spiritual law ———-law of the nations

———-genus: ————— Catholic canon law —————— civil law

———-species: ————– local episcopal law —————— common law

———-subspecies: —————————————————- private vs. public

Note that positive law is written while oral law is not.

Aquinas held that because we were created by God to live a certain way, we can reflect on human nature and discover certain natural guidelines that help us actualize our human potentialities.[4] He calls the latter natural law in morality. Since human nature remains basically the same form culture to culture and century to century, the precepts of the natural law are universal and self-evident to reason. What is good is in accordance with reason and is defined as being in conformity with the natural law of morality:

1. There is a natural tendency among all creatures to preserve their life.

2. All animals seek to preserve their species and care for their offspring.

3. Since we are higher than the beasts, we have an inclination to fully realize all our rational human capacities. This leads to the obligation to seek the truth (for Aquinas, including the knowledge of God) and to follow all the precepts necessary to live harmoniously in society.

People blinded by passion, bad habits, and ignorance are unaware of these natural laws and every will at variance with reason, whether right or erring, is always evil (ST 1-2.19.5).

The Four Laws

1. The eternal law is the rational order that the ruler of the universe established for the creation. All of nature follows these rules blindly, while we have the capacity to obey or disobey them.

2. The natural law is the law available to reason that governs human moral behavior.

3. The divine law is given by revelation. It goes beyond natural law and guides us in achieving eternal happiness. In following this law the natural virtues are surpassed by the theological virtues of faith, hope, and love, which are attained only by Gods grace.

4. The human law is instituted by governments. For it to be legitimate it must be rooted in Gods eternal law. In temporal law (civil law) Aquinas is quoting Augustine, there is nothing just and lawful but what humans have drawn from the eternal law (ST 1-2. 93.3).


[1]David Knowles, The Evolution of Medieval Thought, (New York:  A Vintage Book, Random House, 1962), p. 255 and 256.

[2]Stanley Parry, ed., St. Thomas Treatise on Law, a Gateway Edition, (Washington, D.C.: Regnery Gateway, 1992), p.62.

[3]Ibid., p. ix.

[4] William F. Lawhead, The Voyage of Discovery: a Historical Introduction to Philosophy, (Stamford, CT: Wadsworth Thomson Learning, 2002), p. 171, 178-180. The following as well as most of the diagram above come from Lawhead’s chapter on Aquinas. Lawhead’s diagram comes from page 171.


Written by peterkrey

January 16, 2009 at 3:02 am

Posted in 1, Philosophy

3 Responses

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  1. Can you direct me to a website that has free audio or video lectures of St. Thomas Aquinas’ teachings?

    Rob Argento

    May 31, 2011 at 6:43 pm

  2. […] St. Thomas Aquinas Lecture, Introduction to Philosophy, 2002 […]

  3. […] St. Thomas Aquinas Lecture, Introduction to Philosophy, 2002 […]

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