The Natural Law on Free Will and The Nature of Evil According to St. Thomas Aquinas

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Words: 4191 |

Pages: 9|

21 min read

Published: Oct 22, 2018

Words: 4191|Pages: 9|21 min read

Published: Oct 22, 2018

Table of contents

  1. Introduction
  2. Natural Law
  3. Human Will
  4. Evil
  5. Purposes, Ends, and Flawed Reasoning
  6. Conclusion


The Catholic church teaches that God places the natural law into every human being. Every person conceived possesses the natural law connaturally (Maritain 13). For human beings, this natural law is part of human nature and it informs its possessor of what is good and what is evil. It teaches us to do good and to avoid evil. Human will, therefore, is oriented toward desiring and doing good.

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A question, however, does arise. If every human being possesses the natural law and is oriented toward committing good, why do humans commit evil? To explore this question, we must first understand natural law, the freedom of human will, and what exactly is evil.

Natural Law

In order to understand natural law, we must first agree what we mean when we speak of law. According to St. Thomas Aquinas, law is “nothing else than an ordinance of reason for the common good, made by him who has care of the community, and promulgated” (Summa Theologiae

When this definition of law is applied to God, we find a perfect argument from fittingness. God has a perfect intellect that can reason perfectly. He is the all-powerful ruler of the universe who only desires the supreme good of that which he has created. In creating all things, he has access to all things that exist. If He wishes to promulgate any law to His creation, He can include that law as part of that creation’s nature. In essence, God is the perfect lawmaker.

It is clear then that, since law is “nothing else but a dictate of practical reason emanating from the ruler who governs a perfect community” (Summa Theologiae, there is a law of God. “The world is ruled by Divine Providence… [and] the whole community of the universe is governed by Divine Reason” (Summa Theologiae When we look at the world around us we see order and regularity as if some perfect rational intellect designed everything. It is as if everything in existence follows a law that meant for all things to work in harmony promoting the common good. God’s role as creator and all powerful ruler of the universe “has the nature of law” (Summa Theologiae Since God exists outside of time and is eternal, His law “must be called eternal” (Summa Theologiae hence there is an eternal law.

To be clear, the eternal law is not a law that limits or restrains God as God is a necessary being and “necessary things are not subject to the eternal law” (Summa Theologiae I.II.93.4.) God’s creations, however, are contingent beings. Contingent beings must have a law imposed upon them if only to establish what form and nature a being has. Therefore, “all that is in things created by God, whether it be contingent or necessary, is subject to the eternal law” (Summa Theologiae I.II.93.4.s.c.).

Some may argue that since the totality of God is incomprehensible we cannot possibly comprehend the eternal law with which he governs creation. They argue that only God knows the eternal law. Those people ignore that “a thing may be known in two ways: first, in itself; secondly, in its effect” (Summa Theologiae

While they are right to say that no one except God knows the entirety of eternal law, we do recognize parts of the eternal law by its effects. Since all of creation is governed by the eternal law, we can recognize the portion of the eternal law that applies to a created being by looking at a created being’s nature and end. For example, a rock’s end is to exist. A plant’s end, in addition to existing, is to live.

An animal’s end, in addition to existing and living, is to perceive and react to sensory stimuli. Obviously, the entirety of the eternal law is not present in any of these things, but each of these created beings participate in a part of the eternal law insomuch as their nature allows. The eternal law has governed what their nature is. This participation in the eternal law in accordance to a being’s nature is called the being’s natural law.

Dr. Robert Sokolowski gives a good example of the functioning of natural law in non-rational beings when he speaks of the ends of beings: “The end of a tree is to grow, sprout leaves, nourish itself, and reproduce: to be active and successful as a tree, as an entity of this kind. The end of a zebra is to grow to maturity, nourish itself, reproduce, and live with other zebras. Trees and zebras function well as trees and zebras when they act this way, and we know what a tree and a zebra are when we can say what it means to act well as a thing of this kind. A zebra might break its leg or be eaten by a lion, but possibilities like these do not define what a zebra is. They are not part of what it is, its essence which is displayed most fully not when the zebra merely exists but when the zebra is acting well” (Sokolowski 511-512)

Of all of God’s creation on Earth, human beings are the only ones with a rational soul. It is in the nature of human beings to engage in rational thought. Like the zebra who achieves its end by acting well as a zebra utilizing all of its faculties properly, human beings fulfill their end by utilizing all of their faculties properly especially their most advanced faculty, which is reason. “Man’s last end is happiness” (Summa Theologiae

To achieve their end which is happiness, human beings ought to utilize all of their faculties including reason. Natural law, guiding every being to attain its end, is present in every faculty a being possesses. Therefore, natural law is present in the rational faculties of human beings. Moreover, since it is in the nature of rational beings to apprehend ideas, human beings are capable of reasoning and knowing the natural law, something no other being can do since it is not in their nature to reason or apprehend ideas.

One may ask, what does natural law have to do with morality? Why should one seek to know the natural law besides simply recognizing its existence? According to St. Thomas Aquinas, “natural law is nothing else than the rational creature’s participation of the eternal law” (Summa Theologiae

God is all good and so the eternal law is all good. To participate in the eternal law is so seek the good and for a being to thrive in the nature given to it by God. Natural law, therefore, assists human beings in attaining happiness and avoiding that which undermines it. As St. Thomas Aquinas says, natural law tells us that “good is to be done and pursued, and evil is to be avoided” (Summa Theologiae By following that course of action, we can attain happiness.

Moreover, because natural law guides one to thrive in one’s nature, it is in one’s nature to desire to follow the natural law. In other words, because following the natural law is beneficial, human beings desire to follow it and therefore they desire to do good and avoid evil. “When we say that man is a rational animal, we do not just mean that he is an animal that calculates and draws inferences; we mean, more substantially, that he is an animal that is concerned about living well and not just living” (Sokolowski 508). St. Thomas Aquinas describes the different inclinations of natural law for human beings that guide them toward living well.

First, the natural law drives an “inclination to good in accordance with the nature which he has in common with all substances: inasmuch as every substance seeks the preservation of its own being, according to its nature: and by reason of this inclination, whatever is a means of preserving human life, and of warding off its obstacles” (Summa Theologiae

Second, “there is in man an inclination to things that pertain to him more specially, according to that nature which he has in common with other animals…such as sexual intercourse, education of offspring and so forth” (Summa Theologiae

Third, “there is in man an inclination to good, according to the nature of his reason, which nature is proper to him: thus, man has a natural inclination to know the truth about God, and to live in society: and in this respect, whatever pertains to this inclination belongs to the natural law; for instance, to shun ignorance, to avoid offending those among whom one has to live, and other such things regarding the above inclination” (Summa Theologiae

Those who do not believe in God may argue against the natural law saying that the first two inclinations are simply instincts driven by a Godless evolution while the third inclination is a product of acquired habits and other learned principles. St. Thomas Aquinas disagrees in quoting St. Augustine “’a habit is that whereby something is done when necessary.’ But such is not the natural law: since it is in infants and in the damned who cannot act by it” (Summa Theologiae I.II.94.1.s.c.).

The truth is, acknowledging the existence of natural law does not necessarily require belief in God. Witness to the natural law in human beings is given by extraordinary people who, having grown up in depraved communities with bad roles models and raised by immoral people, exhibit virtuous acts. These people had no way to learn virtue and, more importantly, no reason to practice it—but they still found fulfillment and value in living according to those virtuous principles. “’Virtues are natural.’ Therefore virtuous acts also are a subject of the natural law” (Summa Theologiae I.II.94.3.s.c.). But since these acts of virtue often run contrary to the animalistic desires of the appetitive part of the soul and there is no one to teach virtue to many of those who practice it, natural law must be considered as inscribed ‘in the hearts’ of those who came to be virtuous by their own accord.

Jacques Maritain, in discussing knowledge known to man connaturally says “the precepts of Natural Law are known in an indemonstrable manner. Thus is it that men are unable to give account of and rationally to justify their most fundamental moral beliefs” (Maritain 21). In other words, there are people who hold common moral values with no idea where these moral values came from or what they are based upon. These values often contradict their animalistic desires and interests but they still hold these values to be true. It was as if these values were a part of the individual from the very beginning, like the individual’s limbs and organs.

In line with that “we must say that the natural law, as to general principles, is the same for all, both as to rectitude and as to knowledge” (Summa Theologiae The general principles of natural law are the same in every person. “General principles whether of speculative or of practical reason, truth or rectitude is the same for all, and is equally known by all” (Summa Theologiae These general principles cannot be removed from a person “the natural law, in the abstract, can nowise be blotted out of men’s hearts” (Summa Theologiae In other words, a human being would not be a human being if the natural law of a human being could be removed from it.

That being said, while the general principles of natural law are universal, unchanging, unremovable, and eternal, the conclusions derived from those general principles are not always the same for each individual. Since applying the natural law requires reason, coming to the right conclusions regarding natural law is contingent on reasoning well. We will discuss later how those failures in reasoning come about and how they affect the conduct of the individual but first we must agree on some aspects of human will.

Human Will

“Man has free-will” (Summa Theologiae This “free will is nothing else than the will” (Summa Theologiae I.II.83.4.s.c). itself. “Some things act without judgment; as a stone moves downwards; and in like manner all things which lack knowledge. And some act from judgment, but not a free judgement; as brute animals…because it judges, not from reason, but from natural instinct” (Summa Theologiae As long as an animal is not deprived of its instincts, all non-rational animals of the same species will react the same way to the same stimuli.

A human being “acts from judgment, because by his apprehensive power he judges that something should be avoided or sought” (Summa Theologiae A human’s act of judgement “in case of some particular act, is not from a natural instinct, but from some act of comparison in the reason, therefore he acts from free judgement and retains the power of being inclined to various things” (Summa Theologiae This is the reason why two human beings, faced with the same set of circumstances, may judge the situation in very different ways and be inclined to different courses of action. One may reason correctly and another incorrectly. We see this clearly in the course of “dialectic syllogisms and rhetorical arguments” (Summa Theologiae

Human beings have differences in opinion driven by their different experiences and enabled by their rational mind. Therefore “as man is rational it is necessary that man have a free-will” (Summa Theologiae “The proper act of freewill is choice: for we say that we have a free-will because we can take one thing while refusing another; and this is to choose.” (Summa Theologiae

There are many other things that could be elucidated regarding the human will. For the purposes of discussing the question ‘Why do humans commit evil if they know and desire good?’ it is sufficient to establish the freedom of the human will and its ability to choose that which is good and that which is evil. Which leads to the final concept that needs to be examined: what exactly is evil?


In examining the nature of evil, St. Thomas Aquinas compares it to tis opposite, the nature of good. “The nature of good consists in perfection” (Summa Contra Gentiles I.39.5). Therefore “the nature of evil consists in imperfection” (Summa Contra Gentiles I.39.5). To say something is imperfect means that the thing is missing components that ought to ascribed to it. In other words, evil is a privation of good. “Aquinas thinks of evil or badness as a matter of privation” (Davies 205).

Since God is universally perfect “there cannot be defect or imperfection” (Summa Contra Gentiles I.39.5) in God nor can there be any privation in God. Therefore, there is no evil in God. This is a significant point because it establishes that are no evil principles are included in the natural law as the natural law is a reflection in the eternal law and there cannot be any evil in the eternal law of the all good God.

Evil “is violent and unnatural” (Summa Contra Gentiles I.39.7) but what is evil for one thing can be “natural to a thing according to something within it” (Summa Contra Gentiles I.39.7). For example, eating unhealthy is an evil against the health of the body. But, since unhealthy food tastes good, eating unhealthy food is a good for the sense of taste. With all of this in mind, we now finally able to approach the question: Why do humans commit evil if they know and desire good?

Purposes, Ends, and Flawed Reasoning

No one chooses evil for the sake of evil. Evil is violent and unnatural. Choosing evil for the sake of evil would quickly undermine a person and cause them to perish. Instead, one chooses to commit evil because one perceives that evil as a good. Even a sadist or a masochist who does evil acts does not do them for the sake of the acts themselves but for the enjoyment they get out of doing such acts. At its most fundamental level, enjoyment and pleasure is a good. However, procuring enjoyment by inducing suffering and pain is evil.

A new question arises: how did these people come to see these evil actions as good? If the human end is happiness, how did these people come to believe that their conduct would bring them to happiness? Professor Robert Sokolowski explains that, in addition to having an end like all other beings with a natural law, human beings can bring into existence purposes. Often, these purposes are in privation of good and thereby they are evil.

The difference between ends and purposes is as such: “an end, a telos, belongs to a thing in itself, while a purpose arises only when there are human beings. Purposes are intentions, something we wish for and are deliberating about or acting to achieve. Ends, in contrast, are there apart from any human wishes and deliberations” (Sokolowski 508-509). “Purposes come into existence when human beings set out thoughtfully to do something” (Sokolowski 509). While “ends, in contrast, do not spring into being through human foresight. They do not spring into being at all; they come about concomitantly with the things they belong to” (Sokolowski 509). In other words, purposes are those things that a human being decides to strive for while ends are that which is human being is ordained by God to seek.

In addition, because human beings have a free will, setting purposes has a moral dimension. Our choices in what we set out to do and why we set out to do it can be good or evil. Good purposes are those purposes that are in line with or, at least do not contradict, the ultimate end of man or the thing he utilizes. Evil purposes are those purposes that contradict and/or undermine the end of man or the thing he utilizes.

The way that people come to set a purpose for themselves or other objects is the same way that natural law is reasoned. The human mind prefers sound logical arguments. The general principles of natural law are the premises of moral arguments. Those premises, when used in valid argumentation, lead to a sound conclusion of moral action. In the case of setting purposes, the conclusion is a good purpose in line with a being’s end.

We know however that people do make mistakes in reasoning. Any philosophy professor that has graded undergraduate research papers can attest to the fact that human beings engage in unsound reasoning frequently. Moreover, the general principles of natural law that act as premises, while known, can be ignored because humans have free will to ignore them. Most frequently the third type of inclination of the natural law, dealing with more complex social considerations, are the ones that are ignored. The resulting conclusion from such deficient internal reasoning is unsound. Having included some of the general principles of natural law (as it is impossible to fully ignore and blot the natural law) the deliberator will mistakenly see the conclusion as being good and therefore in line with one’s end of happiness.

For example, the second inclination of natural law informs that sexual intercourse is good. The third inclination of natural law informs when and with whom that sexual intercourse can be done. If someone takes into consideration both sets of inclinations of the natural law, they come to the conclusion that sexual intercourse with one’s spouse at the appropriate time is a good. On the other hand, if someone ignores some or all of the general principles of the third type of inclinations and only considers the second type of inclinations of the natural law, they might come to the conclusion that the evil act of rape is good.

This is not to say that one cannot trust the conclusions of human reasoning, rather that every moral deliberation and discernment of natural law ought to include an examination whether all premises where included and whether those premises are validly used in argument. This is exactly the reason why the Catholic church engages the wisdom of Ecumenical Councils and Synods when developing teachings on morality and faith. The multitude of people allows for mistakes in reasoning to be identified and rectified.

It is worth exploring further how is it that certain premises are ignored and how failures in reasoning occur. Sokolowski gives four examples of how people reason incorrectly when setting a purpose. The first is when one is impulsive. These are people who “have not developed this power of reason, this power of practical categoriality. Their future collapses into their present. Children are naturally impulsive, but some people remain childish even as they get older” (Sokolowski 515).

The second type of failure in reasoning occurs when a person “may have become adult enough to establish distinct purposes and to determine the steps that lead to them, but we may still be unable to appreciate the presence of other people with their purposes. We permit entry into our awareness only of what we want.

We remain unable to see that other people have their viewpoints and needs, that we are not the only agents involved in our situations. To fail to be “objective” in this way is to be what I would like to call ‘morally obtuse’ as opposed to being vicious…such obtuseness is a failure in practical thinking” (Sokolowski 515). An example of such a person is someone who double parks a car. We assume that he didn’t want to injure another person, only that in deciding to park his car their he did not factor in the end of the individual he blocked in.

The third type of failure in reasoning occurs when a person has “state of mind in which we are unable to distinguish what we (and others) want from the demands and obligations of the world itself, that is, we fail to distinguish our purposes from the ends of things…If we merely recognize other people and acknowledge that they too have purposes, all we would have is a world of cross-purposes and ultimate violence, which would amount to a war against all” (Sokolowski 516). Prudent recognition of “the ends of things and the ends of our own nature, however, would help pacify this conflict” (Sokolowski 516).

In other words, in the premises of the argument must include what the ends of that which is involved in deliberation. If tools are to be engaged in setting the premise, then the ends of those tools must be included in the premises. If people, including oneself, is involved in setting the purpose, the human end of happiness must be included in the premises. The natural law of all things involved must be considered in the premises of moral argumentation.

The fourth type of failure in reasoning occurs when a person “may acknowledge the ends of things and the viewpoints of other persons, but we deliberately and malicious let our purposes override them” (Sokolowski 517). These are people who “want to injure others” (Sokolowski 517) because they are either mentally ill or because they have been taught evil habit. Regardless, one can never ignore the totality of the natural law and so the precepts of natural law they do consider still ensures that the deliberator will still seek a conclusion that appears to be good.

People commit all four types of errors in moral reasoning throughout their lives. One may then ask, why would God allow for people to reason moral principles if that risks man reasoning incorrectly? Why wouldn’t God simply have the conclusions of natural law be given to man clearly and without question?

The answer lies in the fact that man, as a rational being, has free will. A rational being must have free will in order to reason by its own faculties. A being cannot be rational if it doesn’t have the freedom to reason. Therefore, man has to be the agent in charge of its own reasoning and freely come to conclusions. If God were to override man’s ability to reach moral conclusions by his own reasoning, that would detract from man’s free will. If man didn’t have free will, it wouldn’t be a rational being. Moral conclusions would be no more than instincts for humans. Man would be nothing more than a brute animal acting according to instinct. If man wasn’t a rational being then it wouldn’t have the nature of a human being as we know it.


All human beings possess the general principles of natural law. Each individual, having reason and free will, is responsible to engage one’s rational faculties to reach conclusions on moral conduct. Human beings, failing to consider all the premises necessary in each situation due to immaturity, flawed teaching, inattention and lack of perspective, make mistakes in reasoning. These mistakes in reasoning in individuals result in misguided conclusions on moral conduct believing that they are good when in fact they are evil.

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No one chooses to commit evil for the sake of evil. Evil is only chosen when it is mistaken as a good. Man seeks to do good because good fulfills the end of man which is happiness. We should take heart in the fact, despite the failings of man, human beings are fundamentally good.

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