As you read all the proofs of God’s existence in our lives, may we be able to strengthen our faith despite all the different blasphemous acts against Him. Through the intercession of the Blessed Mother, may we believe only in our One True God.

EDIT: St. Thomas posited these ways without basing on the Bible or Church teachings… just through pure reason alone!

Way of Motion: Anything in motion is put into motion by something else. A cart is moved by a human, while a human’s movement is influenced by gravity, and so on. This process of motion cannot regress to infinity for that would mean actual motion wouldn’t have started at all. There must be an unmoved mover who first set all things in motion. That unmoved mover is God.

SUMMARY: In the world, we can see that at least some things are changing. Whatever is changing is being changed by something else. If that by which it is changing is itself changed, then it too is being changed by something else. But this chain cannot be infinitely long, so there must be something that causes change without itself changing. This everyone understands to be God.

EXPLANATION: Aquinas uses the term “motion” in his argument, but by this he understands any kind of “change”, more specifically a transit from potentiality to actuality. Since a potential does not yet exist, it cannot cause itself to exist and can therefore only be brought into existence by something already existing.

In Summa contra gentiles I.13.13 Aquinas clarifies “The mover and the thing moved must exist simultaneously”.

Way of Causation: All things were brought about or caused by something. A painting, for instance, was made by a painter. The painter, on the other hand, was born out of the love of his/her parents, and so on. This process of causation cannot regress to infinity for that would mean the series would never have started; meaning, nothing should be in existence now. There must be an uncaused cause who brought about all things into existence. That uncaused cause is God.

SUMMARY: In the world, we can see that things are caused. But it is not possible for something to be the cause of itself because this would entail that it exists prior to itself, which is a contradiction. If that by which it is caused is itselfcaused, then it too must have a cause. But this cannot be an infinitely long chain, so, therefore, there must be a cause which is not itself caused by anything further. This everyone understands to be God

EXPLANATON: As in the First Way, the causes Aquinas has in mind are not sequential events, but rather simultaneously existing dependency relationships: Aristotle’s efficient cause. For example, plant growth depends on sunlight, which depends on gravity, which depends on mass. Aquinas is not arguing for a cause that is first in a sequence, but rather first in a hierarchy: a principal cause, rather than a derivative cause.

Way of Contingency: It is not necessary for all things in the universe to exist; meaning, they are contingent or “possible” things. For a contingent thing to exist, its existence must be caused by a necessary essence. For example, an invention wouldn’t exist without the desire and initiative of an inventor. If everything was merely “contingent” or “possible,” there was a time that nothing existed at all. Nothing comes from nothing. If so, nothing should be existing now. There must be a necessary being — a being who cannot “not exist” — who brought all the contingent things (including the universe itself) into existence. That being is God.

SUMMARY: In the world we see things that are possible to be and possible not to be. In other words, perishable things. But if everything were contingent and thus capable of going out of existence, then, given infinite time, this possibility would be realized and nothing would exist now. But things clearly do exist now. Therefore, there must be something that is imperishable: a necessary being. This everyone understands to be God.

EXPLANATION: The argument begins with the observation that things around us come into and go out of existence: animals die, buildings are destroyed, etc. But if everything were like this, then, at some time nothing would exist. Some interpreters read Aquinas to mean that assuming an infinite past, all possibilities would be realized and everything would go out of existence. Since this is clearly not the case, then there must be at least one thing that does not have the possibility of going out of existence. However, this explanation seems to involve the fallacy of composition (quantifier shift). Moreover, it does not seem to be in keeping with Aquinas’ principle that, among natural things, the destruction of one thing is always the generation of another. Alternatively, one could read Aquinas to be arguing as follows: if there is eternal change, so that things are eternally being generated and corrupted, and since an eternal effect requires an eternal cause (just as a necessary conclusion requires necessary premises), then there must exist an eternal agent which can account for the eternity of generation and corruption. To hold the alternative, namely that an infinite series of contingent causes would be able to explain eternal generation and corruption would posit a circular argument: Why is there eternal generation and corruption? Because there is an eternal series of causes which are being generated and corrupted. And why is there an infinite series of causes which are being generated and corrupted? Because there is eternal generation and corruption. Since such an explanation is not acceptable, there must be (at least one) eternal and necessary being.

Way of Gradation: Things in this world have degrees of perfection (e.g. lesser to greater, smallest to biggest, or least beautiful to most beautiful). These degrees imply the existence of something or someone who possesses the maximum perfection. That being with maximum perfection is God.

SUMMARY: We see things in the world that vary in degrees of goodness, truth, nobility, etc. For example, sick animals and healthy animals, and well-drawn circles as well as poorly drawn ones. But judging something as being “more” or “less” implies some standard against which it is being judged. Therefore, there is something which is goodness itself, and this everyone understands to be God.

EXPLANATION: The argument is rooted in Aristotle and Plato but its developed form is found in Anselm’s Monologion. Although the argument has Platonic influences, Aquinas was not a Platonist and did not believe in the Theory of Forms. Rather, he is arguing that things that only have partial or flawed existence indicate that they are not their own sources of existence, and so must rely on something else as the source of their existence. The argument makes use of the theory of transcendentals: properties of existence. For example, “true” presents an aspect of existence, as any existent thing will be “true” insofar as it is true that it exists. Or “one,” insofar as any existent thing will be (at least) “one thing.”

Way of Intelligent Design: Have you ever wondered why things are the way they are? Why are your eyes in your face and not in your hands? Why do planets revolve around the sun and not the other way around? All things, whether living or non-living, “have this and not that” or “do this and not that.” For example, a robot can only do tasks inputted by its programmer. These qualities and functions inherent in every thing require the direction of an intelligent designer. That designer is God.

Argument from Final Cause or Ends


We see various non-intelligent objects in the world behaving in regular ways. This cannot be due to chance since then they would not behave with predictable results. So their behavior must be set. But it cannot be set by themselves since they are non-intelligent and have no notion of how to set behavior. Therefore, their behavior must be set by something else, and by implication something that must be intelligent. This everyone understands to be God.


This is also known as the Teleological Argument. However, it is not a “Cosmic Watchmaker” argument from design (see below). Instead, as the 1920 Dominican translation puts it, The fifth way is taken from the governance of the world.

The Fifth Way uses Aristotle’s final cause. Aristotle argued that a complete explanation of an object will involve knowledge of how it came to be (efficient cause), what material it consists of (material cause), how that material is structured (formal cause), and the specific behaviors associated with the type of thing it is (final cause). The concept of final causes involves the concept of dispositions or “ends”: a specific goal or aim towards which something strives. For example, acorns regularly develop into oak trees but never into sea lions. The oak tree is the “end” towards which the acorn “points,” its disposition, even if it fails to achieve maturity. The aims and goals of intelligent beings is easily explained by the fact that they consciously set those goals for themselves. The implication is that if something has a goal or end towards which it strives, it is either because it is intelligent or because something intelligent is guiding it.

It must be emphasized that this argument is distinct from the design argument associated with William Paley and the Intelligent Design movement. The latter implicitly argue that objects in the world do not have inherent dispositions or ends, but, like Paley’s watch, will not naturally have a purpose unless forced to do some outside agency. The latter also focus on complexity and interworking parts as the effect needing explanation, whereas the Fifth Way takes as its starting point any regularity. (E.g., that an eye has a complicated function therefore a design therefore a designer) but an argument from final cause (e.g., that the pattern that things exist with a purpose itself allows us to recursively arrive at God as the ultimate source of purpose without being constrained by any external purpose).