Effective Evangelization Based on Aquinas’ Five Ways

If Catholics really want to evangelize effectively,  they have to meet people where they are. Thomas Aquinas’ Summa Theologiae provides five logical arguments for the existence of God which can help modern Catholics discuss faith with unbelievers. The “Five Ways” unite reason with God once again, giving Christians the tools they need to bring people into the Church.

Neoplatonic thought shaped Western civilization as we know it today. The Medieval era was especially keen on this philosophy. Christian theologians combined the logic and reason of philosophers like Socrates, Plato, and Aristotle with classical theism. The result was what is known today as Scholasticism. Scholasticism emphasized and brought to light objective truths about God and his Church through philosophy. Thomas Aquinas and Duns Scotus are particularly well known for many of their works which emphasized philosophical truths about God.

Scholastic thought dominated the West up until the 18th century. Theism was quickly divorced altogether from philosophical reason, giving birth to things like secular humanism, scientism, and atheism.  Atheism and secularism are more popular than ever. 

The Four Causes

Before we dive into the Five Ways it’s important to understand Aquinas’ view of what he referred to as the four causes. These four causes were originally taken from Aristotle and incorporated into Aquinas’ own scholarly works. In Aristotle’s writings such as Metaphysics, he elaborated on the four causes as an understanding of the nature of things, or why things are the way they are. The first cause is the easiest to understand and is known as the material cause. This cause can be ascribed to any tangible thing that is usually discernible by the senses. For example, something as simple as wood or the matter that makes up the human body such as the skeleton, tissues, and nerves.

The second cause requires us to step further into the intellect beyond the senses and ask ourselves how material things come to move or change. This is known as the formal cause, defined by Aristotle as “that from which comes the beginning of the movement” (Aristotle “Metaphysics” 2009 page 9). Wood is not sufficient in and of itself to form into the shape of a particular object, like a bed frame. In the same way, without something in addition to the human body to animate it, it will not move. Therefore the formal cause of the wooden bed frame would be its shape, and what causes the human body to move or be animated would be the human soul.

The Four Causes Cont’d

As we descend deeper into the intellect and ponder the formal cause and the material cause, the question remains of why the wood was shaped into the form of a bed frame, or why we exist in the world with a body and soul. This brings us to the third cause, also known as the efficient cause.  It can be defined as the primary source of change or rest. Aristotle believed the efficient cause must be intellectual. It is often tempting for people to conclude that the person responsible for carving the wood into the shape of the bed frame themselves is the efficient cause.

However, it cannot merely be concluded as a person, because not every person has the skill set needed to carve the wood into the bedframe. A better answer to the reason why the wood was carved into the shape of the bed frame would be the specific art of carpentry. In the same way that the art of carpentry produces the bed frame, we as humans are produced by our parents through procreation. 

The fourth and last cause is known as the final cause. The final cause is simply the final purpose of a thing. The fascinating thing about the final cause is that it can most easily be discussed by examining the nature of things. For example, the final cause of a seed may be to become a plant. The final cause of the bed frame would be for people to sleep on. The final cause of a person is to exist and all that it entails including coming to know and love God. 

The Unmoved Mover: Argument From Motion

Now that we have briefly discussed the four causes, we can dive into each of the five ways. The first way is described as the most manifest. When we think of the word motion, the concept of movement may come to mind. To be more specific to Aquinas, what he means by motion can be more accurately described as change.

Aquinas begins the argument for the first way by stating that “It is certain, and evident to our senses, that in the world some things are in motion.” (Aquinas, ST.1.Q2.A3) If we recall from the four causes,  the easiest to discern by the senses is the material cause. Aquinas is essentially arguing that everywhere we look, all material things that exist around us are constantly changing. 

The Unmoved Mover Cont’d

These changes are dependent on other things, as nothing material is sufficient in and of itself to move or change. He refers to this change as a movement from potentiality to actuality. If my right hand were in front of my face, then it has the potential to move to the right side of my head. But before it can move, motor neurons in my spine have to send the correct signal to my brain, which sends the signal to my muscles. In this same way, everything is changed from the potential to actual by something else actualizing it.

This cannot go on forever. There has to be a first mover to bring the first thing from potential to a state of actuality. This first-mover must be pure actuality in its existence since it was not brought about from potentiality. The first mover is not brought into existence. This pure actuality must also be immaterial since all material things depend on another thing to be brought into actuality. This immaterial, purely actual, and perfect being that exists in and of itself is that which we call God.  

The Argument From Efficient Causes

The third cause is embedded in the second argument for the existence of God. According to Aquinas, there is an order of causes interdependent of each other. Because things are interdependent on other factors outside of itself for existence, no object can be the efficient cause of itself. To use our human example, we as humans cannot be our own efficient causes. To say so is to say that we existed before we came into existence, which is false.

Everything that is brought into existence is dependent on something else. This cannot go on forever because then there would be no first efficient cause. If there’s no first efficient cause, there are no intermediate causes interdependent on each other, which is plainly false, because then nothing would exist. Therefore there must be an efficient cause that is pure actuality and capable of sustaining the universe, without being sustained itself. This first cause is what we know as God. 

The Argument From Necessity 

The argument from contingency is another popular name for the third cause. In the world, everything around us is contingent on something else for existence. This contingency makes it possible to exist or not to exist. It is impossible for these to always have existed because anything that has a possibility to exist at some point did not exist. If this is true and everything is possible or contingent, then nothing existed at some point and even now nothing would exist, which is absurd. Therefore not all beings are possible, but there has to be at least one being who exists by necessity. This being who is necessity and existence itself and is outside of matter is who we call God.  

The Argument From Graduation 

I like to refer to Aquinas’ fourth way as the scale of perfection. The fourth way is the argument that is the most intellectual, and least apparent to our senses in the material world. In this profound approach, Aquinas notes that different degrees of perfection exist for categories of things. An example in the category of unintelligible things like colors demonstrates graduation. People have the inclination to choose more perfect shades of blue or purple according to what those colors are.

If I were to draw two triangles, one made with perfectly straight lines and the other with a zig-zag on one of the three lines and asked someone which triangle is more perfect judging by what a triangle is in its perfection, the person will choose the triangle that doesn’t have the zig-zag. If I were to compare a single rose to a puppy and consider which one is better, I would choose the puppy because it can do certain things that flowers cannot do like move on its own or communicate love and affection.

The scale of perfection also moves into human beings. Let’s say I compared a child to a puppy. The child has more value than the puppy. Humans have an intellect and a rational soul and are therefore created in the image of God. The scale of perfection is used to measure all existent things around us. Yet, it exists in different categories. The question then is how? Aquinas argues that this scale of perfection or graduation of goodness in which we base our judgment is embedded in us. It points to an intellectual and transcendent being. This being is the source of the highest level of perfection and is who we call God.  

The Final Cause 

The fifth way correlates to the nature or final purpose of things. The fourth cause flourishes from this argument. Natural causes incline plants to grow a certain way. Science can better describe this process. The sun’s heat helps produce a multicellular life. A plant will always take root in the ground and grow upwards towards the sun to receive its nutrients. Things that lack intelligence cannot direct themselves according to their own purpose. A being of intellect and knowledge has to direct these objects towards their end. Aquinas uses an example of an arrow shot to the target by the archer.

 This intelligent designer is who we call God. To build on this argument, we can look at how all systems work together towards their end. The distance of the sun makes it possible for life to exist without scorching the surface. To receive nutrients from the sun, a plant must grow upward. Photosynthesis is a process that can best be described as the “storing of energy within a plant from the sun in which the plant converts water and carbon dioxide into oxygen” (Miller, Levine “Miller & Levine Biology” pg. 60). We as humans need oxygen in order to live and fulfill our purpose, and so on. 

In Light of Theology

Science and philosophy are great indicators that point us to the existence of something transcendent. However, it’s important to understand these things in light of Divine revelation. Revelation reveals certain truths about who God is. God’s revelation harmonized with nature and reason was important for Scholastic theologians such as Aquinas.

In Exodus 3:14, God reveals his name to Moses as “I Am”. According to the Church, “This divine name is mysterious just as God is mystery. It is at once a name revealed and something like the refusal of a name, and hence it better expresses God as what he is – infinitely above everything that we can understand or say.” (Catechism of the Catholic Church, 206). God is the essence of being and existence and is beyond what we can understand. Aquinas’ Five Ways provide the necessity of his existence and what he has revealed to us about himself. Such musings stir the human intellect by its nature towards our creator.  

Miller, Kenneth R., et al. “Unit 2: Photosynthesis.” Miller & Levine Biology, Pearson, 2012.

Aristoteles. Metaphysics. NuVision, 2009.  

Aquinas, Thomas. “Question 2. The Existence of God.” SUMMA THEOLOGIAE: The Existence of God (Prima Pars, Q. 2), http://www.newadvent.org/summa/1002.htm.

“The Profession of Faith .” Catechism of the Catholic Church – I Believe in God, http://www.vatican.va/archive/ccc_css/archive/catechism/p1s2c1p1.htm.

-Exodus 3:14