Golden Angel Lawrence OP
“This golden angel surmounts a side altar in Amiens Cathedral.” - The Golden Angel, Fr. Lawrence, OP. Flickr.

Listers, faith and reason are in harmony. The same God that endowed man with reason is the same God that died upon the Cross. To claim that faith and reason are harmonious is to also claim that there is no conflict between theology and philosophy, between Catholicism and science, and between grace and nature. In 1988, St. John Paul II released his encyclical, Fides et Ratio, “Faith & Reason.”1 The opening line reads:

“Faith and reason are like two wings on which the human spirit rises to the contemplation of truth; and God has placed in the human heart a desire to know the truth—in a word, to know himself—so that, by knowing and loving God, men and women may also come to the fullness of truth about themselves (cf. Ex 33:18; Ps 27:8-9; 63:2-3; Jn 14:8; 1 Jn 3:2).” - Pope St. John Paul II, Fides et Ratio.

One reason to take up this subject at the beginning of being formed in the Catholic faith—in a relationship with Christ and his Church—is to best understand how reason and faith are used in our pursuit of God. Moreover, we can come to understand nature as a source of knowledge.

1. What is Faith?

God’s self-communication to humanity is called Divine Revelation.2 Revelation is an “order of knowledge, which man cannot possibly arrive at by his own powers.”3 It contains truths that God must reveal in order for man to know. For example a person may, by reason alone, contemplate the world, study its motion or causality, and deduce that it is logical to believe existence was created by a monotheistic God; however, that same observance of the natural world will not tell you that God is triune or that God came as a Jewish carpenter two-thousand years ago. Certain truths must be revealed to humanity, and Divine Revelation contains those truth that God has revealed. Man’s belief in these truths is called faith. The Church teaches that faith is a “human act by which the believer gives personal adherence to God which invites his response, and freely assents to the whole truth that God has revealed.”4 Faith is the intellectual assent of the believer to truths revealed to man by God.

2. What is the Relationship Between Faith and Reason?

The Catholic Church holds that faith and reason are in harmony. The same God that died upon the cross for our sins is the same God who created human beings as rational animals. Even though faith is an intellectual assent to revealed truths—the submission of our intellect to what we otherwise could not know—God reveals himself in “accordance with reason.”5 Several examples help illuminate how faith interacts with reason.

First, “faith is certain.” In fact, “it is more certain than all human knowledge because it is founded on the very word of God who cannot lie.”6 The certainty of faith perfects natural knowledge. First, divine revelation can give us certitude on a truth we can know by reason. For example, in the Ten Commandments, God tells the Israelites “thou shall not kill.”7 It would be ludicrous to believe that the Israelites and humanity at large did not know that murder was wrong until God’s revelation on Mount Sinai. The revelation is not revealing to humanity something new but is rather granting an assurance, a certitude, to a truth man can know by reason alone. Second, the certainty of faith can perfect reason by elevating a truth that can be known by reason. For example, by reason and reason alone, a person can rationally deduce that there is a monotheistic God; by faith, however, it can be revealed to the person that the monotheistic God is Trinitarian: the Father, Son, and Holy Spirit.8 The rational truth—monotheism—is retained and elevated by the revealed truth of the Trinity. The natural knowledge of God is perfected by the divinely revealed knowledge of God. Faith grants the human intellect a certainty that it otherwise would not have.

Second, Divine Revelation—revealed truth—does not suppress reason, but rather once a truth is revealed, invites the believer to use his or her reason to contemplate the revealed truth. As the Church teaches, “‘Faith seeks understanding’: it is intrinsic to faith that a believer desires to know better the One in whom he has put his faith, and to understand better what He has revealed; a more penetrating knowledge will in turn call forth a greater faith, increasingly set afire by love.”9 Faith, as espoused by Christ’s Church, is “by no means a blind impulse of the mind.”10 For example, the revelation that God is Trinitarian—one God in three persons—does not stop rational inquiry but allows it to flourish by giving it something certain upon which to contemplate. Divine Revelation invites reason to push deeper into the mysteries of God, which in turn can further ignite our love for him and his truth.

Third, all truth is God’s truth, and truth cannot contradict truth. As the Church teaches:

“Though faith is above reason, there can never be any real discrepancy between faith and reason. Since the same God who reveals mysteries and infuses faith has bestowed the light of reason on the human mind, God cannot deny himself, nor can truth ever contradict truth.” “Consequently, methodical research in all branches of knowledge, provided it is carried out in a truly scientific manner and does not override moral laws, can never conflict with the faith, because the things of the world and the things of faith derive from the same God. The humble and persevering investigator of the secrets of nature is being led, as it were, by the hand of God in spite of himself, for it is God, the conserver of all things, who made them what they are.” Catechism of the Catholic Church, n. 159.

Truth cannot contradict itself. The God who made an ordered and observable world is the same God who died upon the Cross. As such, there should always be a harmony between faith and reason, between grace and nature, and between Catholicism and science. Despite popular belief, Catholicism not only holds science to be a good, but nurtured its development in the West. For example, Fr. Roger Bacon, a Franciscan friar (c. 1219/20 – c. 1292) is largely considered the father of the scientific method, Fr. Gregor Mendel, an Augustinian friar (1822 - 1884) is the father of modern genetics, and Msgr. Georges Lemaître (1894 - 1966) developed what is known today as the Big Bang Theory. In short, modern science was made possible through the Church’s understanding of nature and the Church’s establishment of the university system. Overall, faith is a response to God’s self-revelation that perfects reason—it elevates reason to ponder higher truths.

3. What does it mean to be a Rational Animal?

Man is a rational animal. In second century France, St. Irenaeus, a bishop, taught, “Man is rational and therefore like God; he is created with free will and is master over his acts.”11 The Catechism teaches, “God created man a rational being, conferring on him the dignity of a person who can initiate and control his own actions.”12 What does it mean, though, to be rational?—to have reason? One helpful exercise is to compare rational animals, humans, with non-rational animals. As an example, both rational animals and non-rational animals are capable of complex actions. Bees make hives, spiders spin webs, and beavers build dams. Humans also build structures; however, unlike the bee who continually makes the same type of hive over and over, humans have moved from living in caves to skyscrapers. Why? The human, as a rational animal, can understand acts as acts. Whereas the bee is simply carrying out an act, the human is able to comprehend the act itself and thus determine its quality. In this example, humans have been able to understand the action of building as building and have been able to reflect upon it as a craft. As such, humans have moved from caves to skyscrapers as the understanding of the act of building has been improved.

Non-rational animals, though capable of complex actions, are unable to rationally reflect upon their acts. Moved forward by instincts, they carry out the same tasks over and over. To be clear, both rational and non-rational animals have instincts. Both a deer and a person will be startled at a sudden loud noise. The reactions, however, are different. When the deer hears a loud noise, it simply runs always. It does not stop and contemplate, that noise was just a log falling over, I am in no danger. In contrast, if a person startled by a door slamming ran out of the building and a hundred yards into the parking lot before stopping, we would deem their actions irrational. To wit, just as reason allows man to reflect upon his actions, reason also allows man to govern his instincts. The fact that man can reflect upon his own actions and is not a slave to his instincts lies at the heart of morality, because it shows that man is accountable for his actions. A raccoon going through your garbage to find food does not think to himself—is this morally licit? Should I be going through someone else’s trash? No, the raccoon is unable to reflect upon his acts. Similarly, if we catch a raccoon going through our trash, we do not refer to that raccoon as an immoral raccoon. Without the ability to reason, to comprehend our own actions, there would be no moral accountability.13

4. What does it mean to be a Good Person?

Continuing the example of building homes, man has advanced the craft of construction, because he has been able to determine what is good for the craft and what is bad for the craft. The standard of determining what is good and what is bad for construction is its purpose. If the purpose of home construction is to build reliable buildings for shelter, the acts that advance that purpose are good and those that impede its purpose are bad e.g., architectural designs, building materials, etc. As another example, think of a knife. Can a knife be good or bad? Yes, of course. We call a good knife good if it cuts well, and a bad knife bad if it cuts poorly. The determination of good and bad is based upon an understanding of the purpose of the knife—to cut. If one did not know the purpose of a knife, he or she could deduce it from its design—what is its unique function? While the knife could be used for many tasks, its attributes are best actualized when it is used to cut. To the question at hand, what does it mean to be a good person? In order to determine whether a person is good or bad, the purpose of humanity must be understood. Thus, what is the purpose of humanity? The purpose of man is seen in that which is unique to him—his reason; thus, reason, as the unique attribute of humanity, defines the very essence of what man is—a rational animal with a rational nature. Just as the knife is at its best when it cuts and cuts well, so too is man at his best when he reasons and reasons well. The knife, however, is not aware that it is cutting well. The person is aware that he or she is reasoning well. The person can reflect upon the act itself, and as such, can experience a flourishing that comes from living our his or her purpose well, to live well as a rational animal. This flourishing is also known as happiness. A such, if a man reasons well, he is a good man, and if he is a good man, he is happy. Therefore, humanity can achieve a natural happiness if persons, obedient to their rational nature, are good.

If man, by reasoning well, can be good, and all men are rational animals, then can all people, by virtue of being rational, be good? Yes, to an extent, by nature all persons can be good. Regardless of religion, creed, gender, nationality, etc., we expect all persons by their nature to adhere to a certain standard of morality, because by their rational nature, they can contemplate their own actions and be held morally accountable.14 The problem, however, is that rational animals do not always act rationally. St. Paul said it best, “I do not understand my own actions. For I do not do what I want, but I do the very thing I hate.”15 There is something broken within humanity. We fail to even be good according to our own rational nature. By faith, we understand that this brokenness is sin. In response to sin, God has given us a gift, something to perfect our nature, to lift up that which is natural in us, something supernatural—grace. The perfection that grace confers not only helps us to be good according to our nature, but then elevates our nature to goods we otherwise could never attain. For example, by nature, a person can be naturally good, but with grace, the person can be supernaturally good, e.g., burning with the charity that only comes from knowing Christ. As another example, by nature, persons can achieve a natural happiness that comes from living good and rational lives, but by grace that person can experience the supernatural happiness of loving God and someday experiencing God, the Inexhaustible Good, in heaven. In sum, in consideration of humanity, nature and grace are in harmony, and grace will always perfect nature and elevate it beyond its natural capacity. Grace will never impede nature or disorder it, because both nature and grace come from the same source—God.

5. Does God Exist?

After having explored humanity in the context of faith and reason, it may now be beneficial to explore the existence of God in the same. In the beginning of his magnus opus, the Summa Theologica, St. Thomas Aquinas (AD 1225-1274) addresses the question of whether God exists.16 Though he submits five different ways the existence of God may be demonstrated by reason and reason alone, we will take up the first way: the demonstration from motion.17 Aquinas states:

The first and more manifest way is the argument from motion. It is certain, and evident to our senses, that in the world some things are in motion.

When we, as moderns, hear motion we think locomotion, but for Aquinas, he means motion as change. Therefore, his first premise is that all things are in motion or rather are in a state of and are undergoing change.

Now whatever is in motion is put in motion by another, for nothing can be in motion except it is in potentiality to that towards which it is in motion; whereas a thing moves inasmuch as it is in act. For motion is nothing else than the reduction of something from potentiality to actuality. But nothing can be reduced from potentiality to actuality, except by something in a state of actuality. Thus that which is actually hot, as fire, makes wood, which is potentially hot, to be actually hot, and thereby moves and changes it.

Aquinas speaks of motion as the reduction from potentiality to actuality. He further states that in order to move something from potentiality to actuality, the thing must be acted upon by something already in a state of actuality. For example, the golf ball is potentially a hundred yards down the fairway, but that potential is not actualized until the golf club, already in act, swings and hits it. In Aquinas’ example, wood is potentially hot, but that potential will not be actualized unless fire, already in act, moves the wood from being potentially hot to actually hot.

Now it is not possible that the same thing should be at once in actuality and potentiality in the same respect, but only in different respects. For what is actually hot cannot simultaneously be potentially hot; but it is simultaneously potentially cold. It is therefore impossible that in the same respect and in the same way a thing should be both mover and moved, i.e. that it should move itself. Therefore, whatever is in motion must be put in motion by another.

Aquinas submits his second premise: whatever is in motion must be put in motion by another. He observes that a thing cannot be in potentiality and in actuality in the same respect but only in different respects. For example, the golf ball cannot be on the tee in actuality and in potentiality on the tee. It is either on the tee or not. The ball on the tee, however, can potentially be on the fairway, or the bunker, or the green. The fact the golf ball cannot be both on the tee and not on the tee demonstrates the need for something to act upon the golf ball to place it on the tee. Something must actualize its potential to be on the tee. Such it is true with all things, as no thing can be both moved and mover. Thus, whatever is in motion must be put in motion by another.

If that by which it is put in motion be itself put in motion, then this also must needs be put in motion by another, and that by another again. But this cannot go on to infinity, because then there would be no first mover, and, consequently, no other mover; seeing that subsequent movers move only inasmuch as they are put in motion by the first mover; as the staff moves only because it is put in motion by the hand.

The third premise of Aquinas is that there is no infinite regress. Things can only be moved by a mover, which in turn must be moved by something else. Aquinas observes, however, that the regression of motion cannot go on infinitely—something has to start the motion. An infinite beginning never allows for an actual beginning. For example, a sequence of numbers with an infinite beginning, that must start at the beginning, cannot ever begin. As another example, imagine a line of dominos with an infinite beginning and you must knock them over by hitting the first domino. It is impossible. An infinite beginning denies motion; however, as stated in the first premise, we see that motion exists. Consequently, there can be no infinite regress as there must be a beginning.

Therefore it is necessary to arrive at a first mover, put in motion by no other; and this everyone understands to be God.

Since there cannot be infinite regress and we observe that motion does exist, something had to be able to cause the motion without itself needing to be moved. This mover—which would have to be outside all time and space and other forces of motion in the natural reality—has the attributes of what we understand to be God. In this context, God is known as the Unmoved Mover. Aquinas’ argument can be distilled into the following:

We observe that motion exists. All things that move are moved by another. There cannot be infinite regress. Therefore, there must be a First Mover, an Unmoved Mover, God.

Note, however, that this natural demonstration for the existence of God does not necessarily mean that God is personal or even listens to prayer. The truth it conveys is that there is one God and he is the Creator. It tells us another attribute of God as well. Imagine someone gave you the perfect cupcake. What would that mean? It would mean that nothing could be added or removed to make it any better. The potential of the cupcake was fully actualized; thus, when we speak of perfection, what we mean is that there is no potential, because all of it has been actualized. Note that the Unmoved Mover is perfect. If the Unmoved Mover, the First Mover, had any potential, then someone outside of him would have to move on him to actualize the potential; thus, the Unmoved Mover would actually be moved and cease to be that which we know as God. It also means that God could not change, because change implies the potentiality and actuality of motion. As such, another natural name for God is Pure Act, because there is no potential in God. Here, the beauty of our knowledge of God in the context of faith and reason can be seen. For God’s self-revelation, Divine Revelation, gives certitude to these natural truths and never contradicts them. Holy Scripture speaks of God being perfect and being the same yesterday, today, and forever. In addition, Divine Revelation, then, takes these truths and perfects them, allowing us to know the Unmoved Mover as the Most Holy Trinity—a deeply personal God who died to redeem Creation.


  1. Fides et Ratio by St. John Paul II. ↩︎

  2. Catechism of the Catholic Church (“CCC”), n. 50. ↩︎

  3. Id. ↩︎

  4. CCC, Glossary, Faith, cf. 50. ↩︎

  5. CCC n. 156: “So ‘that the submission of our faith might nevertheless be in accordance with reason, God willed that external proofs of his Revelation should be joined to the internal helps of the Holy Spirit.’ Thus the miracles of Christ and the saints, prophecies, the Church’s growth and holiness, and her fruitfulness and stability ‘are the most certain signs of divine Revelation, adapted to the intelligence of all’; they are ‘motives of credibility’ (motiva credibilitatis), which show that the assent of faith is ‘by no means a blind impulse of the mind’. ↩︎

  6. CCC n. 157. ↩︎

  7. See in the Bible, the Old Testament, Exodus 20; Deut 5. ↩︎

  8. For an introduction to the Most Holy Trinity, see RCIA: 8 Questions for those Interested in Becoming Catholic↩︎

  9. CCC n. 158. ↩︎

  10. CCC n. 156. ↩︎

  11. CCC n. 1730. ↩︎

  12. CCC n. 1730. ↩︎

  13. Another example of the difference between rational and irrational animals is universals. For example, the natural inclination toward self-preservation will incline the raccoon to avoid death, but the raccoon is unable to contemplate death itself. If almost hit by a car, the raccoon does not ponder did I almost die? or wait, do all raccoons die? ↩︎

  14. For further discussion on what morality is naturally available to all persons, see the Church’s discussion on virtue, especially the natural virtues or the human virtues. CCC n. 1803, ff. ↩︎

  15. Romans 7:15. ↩︎

  16. Questions - Who is St. Thomas Aquinas? Though the truth of the harmony of faith and reason is rooted in the reality of Jesus Christ, the Logos, the saint who helped the Church understand the relationship between faith and reason is St. Thomas Aquinas (b. AD 1225; d. AD 1274). A large and taciturn man, St. Thomas Aquinas stepped into an age where the relationship between faith and reason, theology and philosophy, grace and nature, were fragmented, debated, and a source of division within the Church. It would be difficult to exaggerate the benefit brought to the Church by the Holy Spirit working in St. Thomas Aquinas. A quick insight into his importance can be grasped by the manner in which the popes throughout history have spoken of him. At the consistorial address of AD 1318, Pope John XXII said, “He (Thomas Aquinas) enlightened the Church more than all the other Doctors together; a man can derive more profit from his books in one year than from a lifetime spent in pondering the philosophy of others.” St. Pius V said Aquinas was “the most brilliant light of the Church,” and in 1879, Pope Leo XIII said “like the sun [Aquinas] heated the world with the warmth of his virtues and filled it with the splendor of his teaching.” In 1974, Pope Paul VI said, “all of us who are faithful sons and daughters of the Church can and must be his disciples, at least to some extent!” The reality of the comment of Pope Paul VI is seen in the fact that save St. Augustine, St. Thomas Aquinas is the most cited Catholic thinker in the Catechism of the Catholic Church. ↩︎

  17. Summa Theologica, I, q. 2., a. 3. ↩︎