Explain Aquinas’ Natural Law Theory

Natural Law is a deontological and absolutist theory created by Thomas Aquinas: a Catholic monk, and one of the founders of the Catholic church. It’s based on Aristotle’s agent centred idea that all human beings having a purpose, and that they need to achieve it in order to flourish and achieve eudemonia. Aquinas believed that all human beings have natural reason given by God that we use in order to flourish and understand God’s plan.
Aquinas suggested that good is revealed in stages of laws; Eternal, Divine, Natural and Human. Eternal laws are principles by which God made the universe, and only he understands completely. Divine laws are seen as a reflection of these. They are laws from the Bible that can only be understood by those who believe in God. Natural laws refer to the moral law of God that has been built into human nature. It’s based on syndersis, which is the idea that you should do good and avoid evil, and so religious belief isn’t needed in order to follow it. Human laws are the laws humans have created, and are based on natural law.
In order to make the identification of morally good actions easier, Aquinas suggested the Primary Precepts. These are five principles that we have to live by, and are absolutist, so all of our actions must fit into the categories in order to be moral. They are preserve life, reproduce, educate and nurture the young, live peacefully in society and worship God. The Secondary precepts are smaller, relativist actions that we can do to achieve the primary precepts. These vary within different societies, and also allow for personal interpretations. For example, in order to preserve life you could become a doctor. Or in order to worship God, you could go to church.
Sometimes two actions conflict. For example, if someone was trying to kill your mother at the top of a cliff, and while defending her you pushed the attacker off the cliff and they die. You are saving your mother, which is preserving life, but by killing the attacker you are acting against the same precept. Aquinas created the Doctrine of the Double Effect for these situations. It states that when faced with a choice between two evils, you should chose the lesser. As long as the resulting negative action wasn’t deliberate (eg. You didn’t intend to kill the attacker) then it’s not immoral. Aquinas also said we need to use our reason in order to tell the difference between real and apparent goods. Sometimes actions seem like they are good and the right thing to do, but they have negative consequences and don’t fit the human ideal- the apparent good. We need to use our reason to find the real good. For example, someone in a bad relationship may have an affair, thinking it’s the right thing to do. However, the real right thing to do would to be to end the relationship before entering another relationship.