St. Thomas Aquinas' Treatise on Law

Instructor: Ashley Dugger

Ashley has a JD degree and is an attorney. She has extensive experience as a prosecutor and legal writer, and she has taught and written various law courses.

St. Thomas Aquinas was a 13th Century theologian, philosopher and priest. In his 'Treatise on Law,' Aquinas explored the origins of law. This lesson briefly explains Aquinas' 'Treatise on Law.'

Source of the Law

St. Thomas Aquinas was a philosopher and priest. He was known for combining theology with philosophy and putting forward theories that combined faith with logical reasoning. Aquinas theorized that both faith and reasoning ultimately come from God, and therefore are naturally meant to go hand-in-hand.

St. Thomas Aquinas penned his

Aquinas used this viewpoint to explore law. He authored Treatise on Law in the mid-1200s. This handwritten commentary uses philosophy and theology to explore the origins of law. According to Aquinas, God is the source of all law.

He explains that 'law' refers to an obligation. For example, you are obligated to travel at a safe speed in your car and not endanger others by breaking the speed limit. But where does this obligation come from? The general obligation exists regardless of whether or not the rule is written down and enacted into an official law. Aquinas determines that the obligation comes from our natural sense of justice and morality, and that natural sense comes from God.

Essence of the Law

Aquinas divided his treatise into several different questions. He poses a question and then provides an answer. One question explores the essence of the law. In other words, when we call something a 'law,' what exactly do we mean?

Aquinas decided that there are four characteristics of all law:

  • An order of practical reason
  • Directed toward the common good
  • Made by someone who cares for the community
  • Promulgated, or publicized

Let's look at these characteristics a little closer. First, a law is an order, meaning it binds, or obligates, a person to a particular behavior. For example, I still have free will and can voluntarily choose to speed down my street anyway. However, my free will is bound to the obligation to obey the speed limit. I use my practical reasoning skills to choose whether or not I will comply with this obligation. According to Aquinas, I will choose based on what brings me the most happiness.

Second, a law is directed toward the common good. This means the law is meant to further the interests and the overall happiness of the community. It's in the best interests of the community to promote safe driving, whether or not I individually find happiness from this law. Though our individual 'goods' might differ, they are all ultimately directed toward overall human happiness.

Next, a law is an order made by someone who cares for the community. Because laws are meant to increase the common good, the community should be permitted to make their own laws. Aquinas says this can be accomplished a couple of different ways. The people can enact their laws, or laws can be made through a representative who works on behalf of the common good.

Lastly, the law must be promulgated. This means the law must be publicized. I cannot be bound, or obligated, to a set speed limit if that speed limit has not been communicated to me. The people must be notified of the laws in order to be obligated to follow them.

Kinds of Law

Aquinas' next question explores kinds of law. Laws can be divided into different categories, based generally on the origin or basis of the law. The kinds of law include:

  • Eternal
  • Natural
  • Human

Let's take a closer look at each.

Aquinas defines eternal law as God's plan for the world. He explains that if God exists, then God must have a divine plan for everything and everyone in this world. That plan serves as the eternal law of the world. The eternal law gives us our ideas of what is 'right' and what is 'wrong', like it is 'wrong' to endanger the safety of others.

Aquinas defines natural law as our participation in the eternal law. It describes the link between the free will of humans and God's will. Remember that Aquinas believes humans will naturally point their actions toward overall human happiness, or the common good. This common good is God's will, meaning we participate in the eternal law through choice and reason. In other words, Aquinas says we participate in the eternal law through the natural law. For example, we naturally know that we should drive safely so that we don't endanger one another, and we will normally obey that natural inclination. That natural inclination is an example of natural law and comes from the eternal law, or God's will for our well being.

To unlock this lesson you must be a Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use

Become a member and start learning now.
Become a Member  Back
What teachers are saying about
Try it risk-free for 30 days

Earning College Credit

Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it risk-free for 30 days!
Create an account