Thomas Aquinas’ 5 Ways of Proving God’s Existence

What are the 5 ways of St Thomas Aquinas?

Thomas Aquinas, medieval philosopher and theologian, systematically exposes in his main works Summa Theologica and Summa contra Gentiles, 5 ways (arguments) that aim to prove the existence of God.

These proofs are one of Thomas Aquinas’ most notable philosophical contributions to the philosophy of religion.

Although it is a topic that strongly involves faith, the 5 Thomistic ways to prove the existence of God are entirely philosophical and rational, that is, they do not resort to the bible or any religious authority.

These are the 5 ways:

  1. Motion;
  2. Efficient Cause;
  3. contingency;
  4. degrees of perfection;
  5. final cause or ends;

The proof of God’s existence is one of the main elements that make up the preambles of faith (preambulum fidei), which is a set of preliminary philosophical truths that underlie the credibility of the Christian faith.

The 5 ways are exposed, in Aquinas’ writings, in a very simple and didactic way, since he intended his writings to his young friends in the convent.

Is it really possible to prove the existence of God?

In the Middle Ages not all Christian philosophers believed that the existence of God could be proven rationally, these are called fideists, because they believed that God was known only by faith and nothing else.

On the other hand, there were those who argued that God’s existence was self-evident.

For Thomas Aquinas, the existence of God can be proved (against fideism), but it is not evident; man has no innate idea of God, nor can he know Him through natural intuition.

For Aquinas, the knowledge of God obtained by reason is, in fact, an imperfect knowledge, since it does not make us know directly the essence of God, but it can provide us, at least, the proof that God is real.

The modes of demonstration: by cause and effect

Before presenting his arguments, Thomas Aquinas distinguishes two types of demonstration: by cause and by effect. The 5 way argument will start from the effects (per effectus) to the cause.

This means that the arguments will always start from the investigation of the sensible beings that we find in the world to then arrive at the transcendent being of God.

These are, therefore, metaphysical arguments. The human intellect, for Thomas, is able to go beyond this physical world and reach the first causes.

1. Proof by movement

Thomas begins by proving the existence of God through movement, which he says is the easiest argument to understand because it is also the most accessible to the senses.

Through our sensory experience, we can perceive that things move.

Thomas Aquinas’ 5 ways are set against the backdrop of Aristotelian philosophy. One of the main concepts in Aristotle’s metaphysics is the notion of movement.

What does movement mean?

Movement means the transition from potency to act, that is, when a possibility (potency) is realized (act). In other words, movement is any kind of change that occurs in beings: for example, the change of color, texture, size, etc.

Therefore, it is not exclusively about local movement, from one place to another.

A blank paper has potency (possibility) to be scribbled on. When I scribble on that paper, it becomes “scribbled paper in act”. A glass has the potency (possibility) of being broken, and when someone breaks it, it becomes “broken glass in act” (possibility that has been realized).

That which caused the movement is called the mover.

Is it possible for something to move itself?

Nothing can move itself, something else is needed to move it.

Take the example of the paper, it cannot scribble itself, nor can the glass break by itself. Something is needed to realize these possibilities (powers).

In the world there is a great connection between the mover and the moved. The mover (the one capable of making the change) is in act, and the moved is in potency. The moved ceases to be potency when it goes into motion, for example, paper scribbled in act is no longer paper with the potency to be scribbled on.

So, if A is in movement, this means that he is moved by something that is in act, this thing is B, but B to be in movement it is necessary C, and so on. However, if we follow this series of events we would go backwards to infinity, and this is impossible. Therefore, we need a first mover that explains the movement of all the others.

The existence of a First Mover

The necessity of having a first mover is undeniable for Thomas, for without it there would be no second mover, and consequently no third mover, and so on. In other words, denying the first mover denies all movement and all change that takes place in the world, which would be absurd, since we see with our own eyes that such changes do take place.

The first mover is unmoved (it never changes), since, if it moved, another mover would be needed before it, and then it would cease to be the first mover, since nothing can move itself.

Knowing that the cause is always superior to the effect, one can reach the conclusion that the first mover is superior to everything moved by it. So, if the first mover is the “strongest” and those moved by it are “weaker”, one can understand that this procedure occurs in a decreasing manner, that is, there is a system of hierarchy that supports these causes.

Therefore, if we go backwards through the causes, and knowing that these causes are stronger than their effects and also knowing that we cannot go backwards infinitely, we arrive at the superior cause, in which all the other causes are interconnected to it, this cause is called the first mover, and this first mover, for Thomas, is what we call God.

2. Proof by the efficient cause

This argument, as far as it goes, is to some extent similar to the previous one, since both establish a succession of events to arrive at a principle of everything.

The efficient cause argument establishes an order of ordered causes, where the cause is always prior to its effect.

Here, as in the first way, it is necessary to go backwards through the causes until arriving at the theoretical necessity of a first cause, since it is not possible to go backwards to infinity, and that one cause depends on another to exist. In this way, the existence of a first efficient cause is necessary, where nothing could come before it.

Therefore, the efficient cause is nothing more than the first cause, the one responsible for all other subsequent causes. The efficient cause was not caused by anything, it simply is, and this first cause, from which all other causes were produced, is what Thomas understands to be God.

3. Proof of contingency

The third way, as Thomas describes it in the Summa, is taken from the possible and the necessary.

The distinction in Thomistic philosophy between being and essence is fundamental to understanding the third way, because existing does not necessarily belong to the essence of beings, that is, non-being does not repugnant to the essence of things.

Both the blank paper and the glass cup cited in the examples above could not exist. Their existence is contingent.

The possible is understood here as contingency, as what can be and not be. Thus, following the second premise of the argument, what can not be does not have existence as its essence. Now, if such a being does not possess existence in itself, then this existence was communicated to it by another being.

That is, if all beings were contingent, they would not exist at some point, and if it did not exist at some point, it would not exist now either, because as said, it is necessary that another being communicates its existence to it.

However, it is clear that contingent beings exist in this world, we ourselves are contingent beings. Therefore, it is not reasonable that only contingent beings exist, but there must be a necessary being, that is, a non-contingent being, the cause of the existence of all contingents.

It is impossible to regress to infinity

The argument again takes up the impossibility of a regression to infinity, because going to infinity one would have no necessary being. Now, the contingent depends on the necessary, so there must be a necessary being by itself.

This necessary being could be necessary, either by itself or by another necessary being.

However, here too one could not go to infinity in the series of necessary beings, because then there would be no necessary being. Therefore, it is also necessary to admit a necessary being by itself, which has not received its existence from any other being. This necessary being is God.

One can see how Thomas’ five ways follow a logical and argumentative pattern, each argument is complemented by the other.

4. Proof by degree of perfection

We find in things something more or less good, more or less true, more or less noble, etc. Now, more and less is said of things insofar as they approach what is in itself the maximum. This implies that such qualities indicate that there is a supreme truth, goodness and nobility.

For Thomas, goodness, truth and nobility are transcendental of beings, that is, everything that exists has such qualities. Being has some properties called transcendental properties. These properties are found in all the special modes that the being comes to take on.

The 5 transcendental

Every being can be considered in itself or in relation to another.

  1. In itself being can be considered a thing or essence (res);
  2. Negatively, as indivisible, or one (unum);
  3. Considered relative to another, being is considered distinct from that other and, therefore, is something (aliquid);
  4. Being is, furthermore, true (verum);
  5. In relation to appetite or tendency, being is good (bonum).

Thus we have five transcendentals, and all these properties are unfoldings of a single notion, that of being.

The Most Perfect Being

This Being must transcend the order of natural beings, for it is the source of all the perfections found in them. These perfections found in natural beings are in this Being, in the highest degree.

This Being is goodness itself, truth, etc. Entities and their finite perfections only participate in their Supreme perfection.

5. Proof by the final cause

The fifth way is easy to understand and is perhaps the most widely used argument to demonstrate the existence of God, because it resorts to an evident fact, which is the order of the universe, both in the order found in each particular being (for example, the highly complex nature of animals) and in the ordered sets of beings (the general cosmic forces and laws).

It is an evident fact that physical bodies, lacking intelligence, cannot tend to an end consciously, or by an act of the will. It is also a fact that we see in nature beings that act with an end in view, and this is seen when they always act in the same way, in order to achieve what is optimal.

The human body, for example, is a collection of organs obviously lacking any intelligence, but which act together (respiratory system, digestive system, etc.) and in harmony to maintain human life.

Now, that which lacks intelligence cannot tend toward an end except through the effect of an intelligent being. Thus, there must be an intelligent being who orders all these natural bodies that make up the harmonious order of the universe.

This intelligent being who orders these natural entities, we give the name of God.


Thomas Aquinas’ 5 ways that lead up to the existence of this necessary Being, first cause, unmoved mover are rigorous and are based on a well-structured metaphysical systematization. The demonstration contains no premise that can be accused of a religious nature, as we have seen.

Thomas became a reference in the question of the existence of God and his nature, alongside great philosophers who sought the same end, such as Plato, Aristotle, Augustine, Anselm and many others.

There has been no lack of objections to the five Thomistic paths over the centuries, and no lack of defense of the paths by the so-called neo-scholasticism.

The question of the existence of God has been present since the birth of philosophy and the question remains open to all kinds of reflection and objection. The extent of the Aquinas’ work and its possible developments would prevent any definitive judgment.

Cite This Work

Vieira, S. (2021, July 01). Thomas Aquinas’ 5 Ways of Proving God’s Existence. Filosofia do Início. Retrieved from

Vieira, Sadoque. “Thomas Aquinas’ 5 Ways of Proving God’s Existence.” Filosofia do Início, July 1, 2021.

Vieira, Sadoque. “Thomas Aquinas’ 5 Ways of Proving God’s Existence.” Filosofia do Início, 1 Jul. 2021,


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