Aquinas' Four Types of Law - Summa Theologiae Prima Secundae - Questions 90 - 95

Law In General

In these questions, I -II 90 - 95, Thomas builds an argument for an objective law-based morality. He talks about four types of law. Interestingly, in his conception, they are not at odds with one another. Rather, they are four types of law which are nested within each other. Each more law deals with its own unique set of more specific circumstances, but none of them are contradictory. There is the positive law, which is nested in the natural law, which is nested in the divine law, which is nested in the eternal law

(In a lot of ways it is a very similar description to the one that Jordan Peterson gives for a non-relativist morality in his Maps of Meaning course. There, Peterson argues that in order to act in the world at all it requires the experience of value, i.e. some drive towards the experience of something as good. But one cannot know how to act in a world of so many complex values without belief structures that organize one’s perceptions. These structures guide us in ignoring most of reality in order to focus on what is authentically valuable for me as a human being.) 

For Aquinas, happiness (in the broadest sense of the word meaning something like highest fulfillment) is both the impetus of action and the final goal of action. It is both the movement within us that pushes us forward, and the end outside of us which beckons us in its direction. It is law, through both reason and faith, that acts as the organizing belief structure that helps us attain that highest good as end. There is always a paradox present with law and freedom, though. Authentic law interacts with freedom in two inverse ways. Law limits our freedom in the sense of a freedom of choice. It tells us what we cannot do. At the same time, there is an inverse relation to freedom in the sense of doing what is best for us. By limiting our freedom of choice it shows us the pathway to choose what is actually best for us and will make us happiest in the long run. Like the lines on the road which show us where to drive so that we do not crash into other people, the law guides us through life to our highest end. All that to say is that happiness and law are not contradictory to one another, they are necessary for one another. Like having the instructions to playing a board game, you then can actually play it and have a good time.

Eternal Law

Eternal law is the deepest sense of law in which all other forms are nested. This is because the eternal law is the nature of God himself. This law, in its fullness, transcends our understanding, but we do have glimpses of it as we begin to understand who God is. The eternal law is reflected somewhat, though, in the ordering of creation, as God is its creator. Therefore, since creation has a nature grounded in the eternal nature of God, it also has proper ends which are ordained for us in the same manner. 2 Here we can see why Aquinas holds that we have a common human nature, because we can speak about objective morality emanating from the objective nature of God's eternal essence. Thus, eternal law is something like God’s eternal conception of things which is written into nature as its highest and ultimate ordering principle, and which moves any secondary or more specific conception of nature. 3

Natural Law

Due to God's eternal law of himself there is written in all things a nature, or a natural way in which they are made to operate. This is first understood by the inclination of the human spirit towards goodness. With experience we can then use reason to comprehend general and self-evident principles that guide us in this inclination in the right way. From there we can apply these principles in a more specific way to practical human laws. 4 Although, when it comes to applying those principles to practical details there is often disagreement because of certain obstacles like: “perverted passions, evil habits, and evil dispositions.” This may be an explanation why certain cultures or time periods may have struggled to apply the natural principles with rectitude. 5 (Aquinas gives first principles of the natural law which are most evident to everyone, but as one logically extrapolates further and further from those principles it becomes harder for everyone to grasp. For example, "do good and avoid evil" is the most universal principle which everyone can agree on. From there one can talk about a natural law to protect the innocent, marry and reproduce, live in community, seek education and understanding, and honor the creator as authentic manifestations of human nature.)

Divine Law

While man’s proper end can be discerned partly from inclination and reason about his earthly experience, man also has a transcendent end which is not as clear to him. This is to be with God himself in the afterlife. Therefore, he needs revealed guidance regarding this transcendent end to help him understand it and also get there. The divine law also helps clarify matters which are unclear to the natural law because of sin and variation amongst humans. 6 (By revealed here Aquinas is talking about religious law. That God would directly speak to us through his son Jesus Christ and give us guidance about how to live and embrace salvation. This is the religious law of the Church.) 

Human Law

Finally, human law, or positive law, is the application of rational moral principles of the natural law to more and more specific situations. We need guidance in these specifics because while nature gives us reason, we must train and practice in order to use it properly. Also, some people need more severe threats and punishments to get them to practice the right thing, while others do not. Thus human laws help ensure peace for all. 

We derive positive law from natural law principles in two ways. (1) As conclusions demonstrated from principles and (2) by “determination,” as like in artistic work where the form is instantiated into the particular; the details may be variant yet be the same in form. When the human law is derived from the natural law in the first way, (1) it has the objective force of natural law, but in the second way (2) it does not necessarily have objective force. 7

Some Thoughts on Teleology

I will be updating this post with these thoughts in a bit. 


1 - Aquinas, Thomas. Summa Theologiae. Q90, A1-2. 

2 - Q91 A1-4.

3 - Q93 A3. 

4 - Q91 A1-4.

5 - Q94 A4.

6 - Q91 A1-4.

7 - Q95 A1.