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7.4.3: Natural Law Theory

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    Aquinas’s Natural Law Theory contains four different types of law: Eternal Law, Natural Law, Human Law and Divine Law. The way to understand these four laws and how they relate to one another is via the Eternal Law, so we’d better start there…

    By “Eternal Law’” Aquinas means God’s rational purpose and plan for all things. And because the Eternal Law is part of God’s mind then it has always, and will always, exist. The Eternal Law is not simply something that God decided at some point to write.

    Aquinas thinks that everything has a purpose and follows a plan. He, like Aristotle, is a teleologist (the Greek term “telos” refers to what we might call a purpose, goal, end/or the true final function of an object) (see Chapter 1.3; not to be confused with a telelogical ethical theory such as Utilitarianism) and believes that every object has a telos; the acorn has the telos of growing into an oak; the eye a telos of seeing; a rat of eating and reproducing etc. If something fulfils its purpose/plan then it is following the Eternal Law.

    Aquinas thinks that something is good in as far as it fulfils its purpose/plan. This fits with common sense. A “good” eye is one which sees well, an acorn is a good if it grows into a strong oak tree.

    But what about humans? Just as a good eye is to see, and a good acorn is to grow then a good human is to…? Is to what? How are we going to finish this sentence? What do you think?

    Aquinas thinks that the answer is reason and that it is this that makes us distinct from rats and rocks. What is right for me and you as humans is to act according to reason. If we act according to reason then we are partaking in the Natural Law.

    If we all act according to reason, then we will all agree to some overarching general rules (what Aquinas calls primary precepts). These are absolute and binding on all rational agents and because of this Aquinas rejects relativism.

    The first primary precept is that good is to be pursued and done and evil avoided. He thinks that this is the guiding principle for all our decision making.

    Before unpacking this, it is worth clarifying something about what “law” means. Imagine that we are playing Cluedo and we are trying to work out the identity of the murderer. There are certain rules about how to move around the board, how to deal out cards, how to reveal the murderer etc. These rules are all written down and can be consulted.

    However, in playing the game there are other rules that operate which are so obvious that they are neither written down nor spoken. One such rule is that a claim made in the game cannot both be true and false; if it is Professor Plum who is the murderer then it cannot be true that it is not Professor Plum who is the murderer. These are internal rules which any rational person can come to recognize by simply thinking and are not external like the other rules — such as you can only have one guess as to the identity of the murderer. When Aquinas talks of Natural Laws, he means internal rules and not external ones.

    Natural Law does not generate an external set of rules that are written down for us to consult but rather it generates general rules that any rational agent can come to recognize simply in virtue of being rational. For example, for Aquinas it is not as if we need to check whether we should pursue good and avoid evil, as it is just part of how we already think about things. Aquinas gives some more examples of primary precepts:

    1. Protect and preserve human life.
    2. Reproduce and educate one’s offspring.
    3. Know and worship God.
    4. Live in a society.

    These precepts are primary because they are true for all people in all instances and are consistent with Natural Law.

    Aquinas also introduces what he calls the Human Law which gives rise to what he calls “Secondary Precepts”. These might include such things as do not drive above 70mph on a motorway, do not kidnap people, always wear a helmet when riding a bike, do not hack into someone’s bank account. Secondary precepts are not generated by our reason but rather they are imposed by governments, groups, clubs, societies etc.

    It is not always morally acceptable to follow secondary precepts. It is only morally acceptable if they are consistent with the Natural Law. If they are, then we ought to follow them, if they are not, then we ought not. To see why think through an example.

    Consider the secondary precept that “if you are a woman and you live in Saudi Arabia then you are not allowed to drive”. Aquinas would argue that this secondary precept is practically irrational because it treats people differently based on an arbitrary difference (gender). He would reason that if the men in power in Saudi actually really thought hard then they too would recognize that this law is morally wrong. This in turn means that Aquinas would think that this human law does not fit with the Natural Law. Hence, it is morally wrong to follow a law that says that men can, and women cannot, drive. So although it is presented as a secondary precept, because it is not in accordance with Natural Law, it is what Aquinas calls an apparent good. This is in contrast with those secondary precepts which are in accordance with the Natural Law and which he calls the real goods.

    Unlike primary precepts, Aquinas is not committed to there being only one set of secondary precepts for all people in all situations. It is consistent with Aquinas’s thinking to have a law to drive on the right in the US and on the left in the UK as there is no practical reason to think that there is one correct side of the road on which to drive.

    It is clear that on our own we are not very good at discovering primary precepts and consequently Aquinas thinks that what we ought to do is talk and interact with people. To discover our real goods — our secondary precepts which accord with Natural Law — we need to be part of a society. For example, we might think that “treat Christians as secondary citizens” is a good secondary precept until we talk and live with Christians. The more we can think and talk with others in society the better and it is for this reason that “live in society” is itself a primary precept.

    But looking at what we have said already about Natural Laws and primary and secondary precepts, we might think that there is no need for God. If we can learn these primary precepts by rational reflection then God simply drops out of the story (recall the Euthyphro dilemma above).

    Just to recap as there a lots of moving parts to the story. We now have Eternal Law (God’s plans/purpose for all things), Natural Laws (our partaking in the Eternal Law which leads to primary precepts), Human Laws (humans making specific laws to capture the truths of the Natural Laws which lead to secondary precepts) and now finally Aquinas introduces the Divine Law.

    The Divine Law, which is discovered through revelation, should be thought of as the Divine equivalent of the Human Law (those discovered through rational reflection and created by people). Divine laws are those that God has, in His grace, seen fit to give us and are those “mysteries”, those rules given by God which we find in scripture; for example, the ten commandments. But why introduce the Divine Law at all? It certainly feels we have enough Laws. Here is a story to illustrate Aquinas’s answer.

    A number of years ago I was talking to a minister of a church. He told me about an instance where a married man came to ask his advice about whether to finish an affair he was having. The man’s reasoning went as follows — “I am having an affair which just feels so right, we are both very much in love and surely God would want what is best for me! How could it be wrong if we are so happy?”

    In response, the minister opened the Bible to the Ten Commandments and pointed out the commandment that it says that it is wrong to commit adultery. Case closed. The point of this story is simple. We can be confused and mistaken about what we think we have most reason to do and because of this we need someone who actually knows the mind of God to guide us, and who better to know this than God Himself. This then is precisely what is revealed in the Divine Law.

    Or consider another example. We recognize that we find it hard to forgive our friends and nearly always impossible to forgive our enemies. We tell ourselves we have the right to be angry, to bear grudges, etc. Isn’t this just human? However, these human reasons are distortions of the Eternal Law. We need some guidance when it comes to forgiveness and it is where the Divine Law which tells us that we should forgive others — including our enemies. Following the Human Laws and the Divine Laws will help us to fulfil our purposes and plans and be truly happy.

    7.4.3: Natural Law Theory is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.