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The Natural Law: A Guide for How to Be Human

The Catholic Church is often ridiculed when it comes to its moral teachings. Whether it’s Church teaching on contraception, so-called “same-sex” marriage, the acting out of transgender ideologies, homosexual acts, or abortion, popular culture tends to view the Church as some evil tyrant trying to tell people how to live their lives.

What amazes me is how little the Church’s critics understand why the Church teaches such things. They fail to realize that behind the teachings about which specific acts are right or wrong is the general standard of determining what constitutes appropriate and inappropriate human behavior, which in turn rests on an understanding of what constitutes the good and the bad.

A good or bad triangle?

When we speak of the terms good and bad, we necessarily reference the nature or essence of something. For example, let’s say we have two triangles, one drawn on the back of a cracked seat on a moving bus and the other drawn with a straight edge on a piece of paper at a stationary desk.

Which do you think would be a good example of a triangle? Obviously the good triangle would be the one drawn with a straight edge on a piece of paper at the desk. But we have to ask, “Why?”

The answer is because the triangle drawn with a straight edge instantiates triangularity better than the one drawn on the cracked bus seat—that is to say, it best represents what a triangle is supposed to be. Notice that in determining which triangle is good and bad we implicitly compare each to what a triangle is—its essence or nature.

A good or bad oak tree?

Consider now an oak tree. Let’s say we have one oak tree that has strong roots and sinks its roots deep into the ground, and the other has weak roots and doesn’t sink its roots deep into the ground. Which one is the good oak tree? Which one is the bad?

Obviously, the former is the good oak tree, since it does what an oak tree is supposed to do given its nature—that is to say, it achieves the ends its nature directs it toward (e.g., sinking deep roots into the ground, taking in nutrition, and growing). Notice once again nature determines what is a good or bad instance of a thing.

The oak tree’s nature also helps us determine what is good and bad for the tree. If we were to spray the tree with poison, would the oak tree achieve its natural ends of sinking roots deep into the ground, taking in nutrition, and growing? Of course not! Therefore, we can say that poison is bad for the tree given its nature. And notice that what is bad for the tree is independent of what you are I think; it is an objective fact.

By contrast, if we water the tree, fertilize it, and allow it the light it needs, it will achieve the ends its nature directs it toward. As such, we can conclude that water, fertilizer, and light are good for the tree. And notice once again our judgment about what is good is independent of what you or I think. What is good for the tree, given its nature, is an objective fact.

So, for living things we appeal to nature not only to determine whether it is a good instance of the kind of thing it is but also what is good and bad for the thing given the ends its nature directs it toward.

A good or bad human being?

The same reasoning applies to human beings. Human beings have a nature or essence with various capacities and ends the fulfillment of which is good and the frustration of which is bad, as a matter of objective fact.

For example, nature directs us to preserve our own existence. This is something we share with all living things. Nature also directs us to preserving our species through sexual intercourse and rearing children—something we share with animals specifically. Finally, nature directs us to certain ends or goals that are peculiar to us as rational animals—namely, to know the truth about God, to live in society, to shun ignorance, and to avoid harming those with whom one has to live.

Therefore, we can know what is good and bad for human beings objectively speaking. Any behavior that facilitates the achievement of these natural ends is considered good—that is to say, it will fulfill human nature. Any behavior that frustrates the achievement of these natural ends is considered bad—that is to say, it won’t bring about human flourishing.

Human nature therefore serves as a standard for what is good and bad behavior for human beings and it is independent of what you or I think. On this analysis, what is good and bad behavior is an objective fact.

Now, since it belongs to our rational nature to do good and avoid evil (see Summa Theologiae I-II:94:2), and the good is the achievement of the ends nature directs us toward, the rational person will perceive those ends and behave in a way that facilitates their achievement. The person who chooses to behave in a way that frustrates man’s natural ends acts irrationally. And because man is free to behave in either way, he will be either worthy of praise or blame depending on his choice.

So, to the moral skeptic’s question “Why should I do what is good?” the answer is, as the philosopher Edward Feser writes, “[B]ecause to be rational just is (in part) to do what is good, to fulfill the ends set for us by nature” (Aquinas: A Beginner’s Guide, ch. 5).

The formulation of general moral principles on the basis of human nature’s capacities and ends and the systematic working out of their implications is what the Catholic Church has called in her Tradition the natural law. Charles Rice, an American legal scholar, defines the natural law as “a set of manufacturer’s directions written into our nature so that we can discover through reason how we ought to act” (50 Questions on the Natural Law, ch. 1).


It is this natural law that the Catholic Church has always appealed to in defense of its prohibition of certain behaviors. Whether it’s contraception, homosexual acts, or abortion, the Church sees in these behaviors a frustration of certain ends our nature directs us toward, and as such cannot contribute to human flourishing—that is to say, they cannot contribute to authentic human happiness. In this sense they are bad. Since the Church is in the business of leading us to authentic human happiness, it says no to such behaviors.

Rather than being an evil tyrant trying to limit everyone’s freedom, the Church is simply trying to be a voice for what it means to be human and how to flourish as one. What’s so bad about that?

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