Natural Law Ethics (St. Thomas Aquinas’s Christian Ethics)

Natural law ethics is a popular name attributed to the model of ethics developed by St. Thomas Aquinas during the Medieval period. Because it was developed by St. Thomas Aquinas, natural law ethics is also called Thomistic ethics.

The basic idea in natural law ethics is that “Reason” is the source of the moral law and that it directs us towards the “Good”. According to Aquinas, the “Good” is the ultimate goal of the person’s actions. And for Aquinas, the “Good” is discoverable within the person’s nature. This explains why the basic goal of natural law ethics is “to do good and avoid evil”.

Now, how do we know that a person is acting rightly or wrongly?

According to Aquinas, an act is morally right if it is done in accordance with the moral law. But what is the moral law?

As already mentioned, “reason” is the source of moral law; hence, the moral law is the dictate of reason. But for Aquinas, the moral law comes from God’s Eternal Law. Indeed, for Aquinas, the moral law is the Divine Law expressed in human nature, which reads: “Do good and avoid evil.”

If the moral law is “doing good and avoiding evil,” how do we know that one is acting in accordance with the good?

According to Aquinas, the “good” is that which is suitable to human nature or that which is proper to human nature. And for Aquinas, we know that an action is good, that is, suitable to human nature, if it is done in accordance with conscience.

Aquinas understands conscience as the inner voice of the intellect or reason which calls the human person to follow the moral law, that is, to do good and avoid evil. As we can see, in natural law ethics, conscience serves as the guide in making moral decisions.

But how do we know that one’s action obeys conscience?

According to Aquinas, an action obeys conscience if it satisfies the three-fold natural inclination of the human person, namely: 

1) self-preservation, 2) just dealing with others, and 3) propagation of human species.

Self-preservation, for Aquinas, is a natural inclination that urges the human person to take care of her health or not to kill or put herself in danger. This explains why for Aquinas suicide is absolutely wrong.

Just dealing with others urges us to treat others with the same respect that we accord ourselves. Thus, for Aquinas, all forms of inhumanities, such as exploitation, seduction, deception, manipulation, cheating, kidnapping, murder, and intimidation, are absolutely wrong too.

In terms of the propagation of human species, Aquinas believes that the reproductive organ is by nature designed to reproduce and propagate human species. Any act of intervention, therefore, that frustrates the very purpose of the reproductive organ is unnatural, hence immoral. This explains why even masturbation is immoral in natural law ethics.

It must be noted that for Aquinas if at least one of these three natural inclinations of the human person is violated, then an act does not obey conscience; it is therefore immoral. Needless to say, for an action to be considered moral in natural law ethics, it must be done in accordance with conscience. Again, it must be done in accordance with the moral law, that is, “doing good and avoiding evil”.

Three Determinants of Moral Actions

In addition to the three-fold natural inclinations of the human person, Aquinas introduced three things that determine the morality of a human act, namely:

1) object of the human act, 
2) its circumstance, and 
3) its end.

The object of the act refers to that which the will intends primarily and directly. It may either be a thing or an action. Take, for example, the physician’s act of removing a tumor. As we can see, the direct object of the act is “to remove a tumor”. Please note that the circumstance and the end are also intended here, but not directly.

The circumstance refers to the condition which affects the morality of an action. It is important to note that the circumstance may aggravate or mitigate the morality of the human act.

Aquinas classified circumstance into:

1) quality of a person (who), 
2) quality or quantity of the moral object (what), 
3) the circumstance of place (where), 
4) the circumstance of means (by what means), 
5) the circumstance of end (why), 
6) manner in which the action is done (how), and 
7) time element involved in the performance of the action (when).

As to the first, it is bad to rape a woman, but it is worse to rape a daughter.

As to the second, the act of a taxi driver who returns a wallet containing a couple of thousand dollars is good in itself, but that of one who takes the initiative of returning fifty thousand dollars left by a tourist is even better.

As to the third, smoking in public may not be good, but it is worse if one smokes inside a church.

As to the fourth, to pray for a sick person is good in itself, but to give her money for medicine for her medication is better.

As to the fifth, helping an orphan kid finish schooling is good, but doing it with the intention of employing her later is better.

As to the sixth, killing might generally be conceived as evil. But in the case of unjust aggression, it might be morally right to kill the aggressor.

And as to the seventh, it might not be a good idea to smoke inside the church, but it is worse to do it while the mass is going on.

The end of the act refers to the purpose of the doer or the agent of the human act itself. According to Aquinas, it can be taken as a circumstance because the end is an integral part of every moral act. For example, marrying a person one is engaged to is good in itself. But doing so while motivated by the selfish end of, say, taking a big share of an inheritance, makes the whole action morally wrong.

It must be noted that for Aquinas, all the three determinants of a human act must be all good for an act to be considered good or morally right.

Four Principles of Double Effect

Sometimes a human act may produce two conflicting results, that is, one is good and the other is evil. To address this dilemma, Aquinas formulated the four principles of double effect, namely:

1. The action intended must be good in itself, or at least morally indifferent; otherwise, the act is evil at the very outset;
2. The good effect must follow the action at least as immediately as the evil effect, or the good and evil effects must occur simultaneously;
3. The foreseen evil effect should not be intended or approved, but merely permitted to occur; and
4. There must be a proportionate and sufficient reason for allowing the evil effect to occur while performing the action.

According to Aquinas, all of the 4 principles must be satisfied for an action to be considered morally right.

Let us take for example the act of removing a cancerous uterus of a pregnant woman which necessarily implies abortion. As we can see, the act will produce two results, one good and the other is evil. Of course, the removal of the cancerous uterus of the pregnant woman will definitely save her life (good result) but at the same time, it will kill the fetus (evil result). So, what is the morality of the action if we apply Aquinas’s four principles of double effect?

Please note that the act is simply to remove the cancerous uterus. So, obviously, we satisfy principle #1 because the intention of removing the cancerous uterus is good in itself. We may even view it as morally indifferent.

We also satisfy principle #2 because the good effect, that is, the recovery of the pregnant woman follows the action immediately. And even if the fetus dies after the removal of the cancerous uterus, at least this evil effect occurs simultaneously with the good effect.

Principle #3 is also satisfied because abortion, that is, the death of the fetus, was not intended. It was just allowed to happen. As we can see, the main intention of removing the cancerous uterus of the pregnant woman is to save her life. Even if the death of the fetus was foreseen, according to Aquinas, it was just allowed to occur.

And lastly, principle #4 is also satisfied because there is indeed a sufficient reason for allowing the evil effect, that is, abortion or the killing of the fetus, to happen. Needless to say, if we don’t remove the cancerous uterus, then we lose both the lives of the woman and the fetus. But if we remove the cancerous uterus, at least, as Aquinas would have us believe, we save one life.

As we can see, the removal of a cancerous uterus of a pregnant woman which implies abortion is morally right.

Let us take another example, that of killing a drug lord. As is well known, illegal drugs have been destroying many lives both young and old. So, killing a drug lord will produce a good result. However, the act produces an evil result too, that is, murder. So, what is the morality of the act of killing the drug lord from the vantage point of Aquinas’s 4 principles of double effect?

A utilitarian may argue that the act of killing the drug lord is good as it may produce more benefits, that is, greatest happiness, to the greatest number of people concerned. However, for Aquinas, the act of killing the drug lord is intrinsically immoral because, as we can see, it does not satisfy the first principle of the 4 principles of double effect. The first principle says that the act must be good in itself or at least morally indifferent. But the act of “killing” (the drug lord) is evil in itself. Hence, even if this act produces more benefits to many people concerned, for Aquinas, it is absolutely immoral. This explains why the Roman Catholics, who adhere to Aquinas’s natural law ethics, strongly oppose extrajudicial killing (EJK) in general and killing a drug lord in particular.

Now, since the first principle is violated, we need not proceed and check the remaining principles because in the first place the act is already immoral. `