Does God Exist?

Sep 13

The Catholic Case for Knowing God by Reason

Short Answer

Yes. God exists, and His existence is not something that Catholics are required to accept by a blind leap of faith. The Catholic Church teaches that human reason, beginning with the created world around us, is capable of arriving with certainty at the existence of the one true God. St Paul teaches that God's invisible attributes are known through the things He has made:

“For the invisible things of him, from the creation of the world, are clearly seen, being understood by the things that are made.”— Romans 1:20

The First Vatican Council solemnly defined this principle in Dei Filius in 1870. It taught that God, “the beginning and end of all things,” can be known with certainty by the natural light of human reason from created things. The Council went so far as to condemn the contrary proposition. This is therefore not merely the opinion of St Thomas Aquinas or one philosophical school; the capacity of human reason to know God from creation is Catholic doctrine solemnly taught by an Ecumenical Council.

This does not mean that reason by itself discovers everything Christianity teaches. Reason can establish that there must be a first, necessary, uncaused and transcendent source of all finite reality, possessing the perfections appropriate to God. But mysteries such as the Trinity, the Incarnation and man's supernatural destiny require divine revelation. The first question is therefore not yet “Is Catholicism true?” but more fundamentally: Does reality itself point beyond the universe to God?

The Catholic answer is yes.

Why This Question Matters

Almost every other religious question depends upon this one.

Before asking whether Jesus Christ is God, whether He rose from the dead, whether He founded a Church, whether Scripture is inspired, or whether the Catholic Church is that Church, a more basic question must be addressed: Is there a God at all?

If there is no God, Christianity cannot be true. Prayer is meaningless, divine revelation is impossible, objective duties toward a Creator do not exist, and questions about Christ and His Church become merely historical or cultural.

But if God exists, the situation changes fundamentally. Man is no longer a self-originating accident existing in a universe without ultimate explanation. He is a creature whose existence depends upon a Creator. Questions of purpose, moral obligation, worship, revelation and salvation then become unavoidable.

The Catholic approach is important because it rejects two opposite errors.

The first is rationalism, which treats human reason as though it were capable of discovering by itself every truth necessary for man's supernatural destiny.

The second is fideism, which treats religion as though belief in God had no rational foundation and must simply be accepted by an act of faith.

Catholicism teaches neither. Reason really can know that God exists; revelation then tells us truths about God which reason alone could never discover.

What the Catholic Church Teaches

Sacred Scripture

Sacred Scripture repeatedly presents creation as bearing intelligible witness to its Creator.

St Paul writes:

“For the invisible things of him, from the creation of the world, are clearly seen, being understood by the things that are made; his eternal power also, and divinity.”— Romans 1:20

The Book of Wisdom makes essentially the same argument. Speaking of men who admire the visible universe but fail to recognise its Creator, it says:

“For by the greatness of the beauty, and of the creature, the creator of them may be seen, so as to be known thereby.” — Wisdom 13:5

The Psalms likewise declare:

“The heavens shew forth the glory of God, and the firmament declareth the work of his hands.” — Psalm 18:2 in the Douay-Rheims numbering.

These passages do not present God merely as an emotional explanation offered to fill gaps in human knowledge. They present the created order itself as intelligible evidence from which the Creator can be known.

The First Vatican Council

The most precise pre–Vatican II doctrinal statement is found in the Dogmatic Constitution Dei Filius, promulgated by Pope Pius IX with the First Vatican Council on 24 April 1870.

Chapter II teaches:

“The same holy Mother Church holds and teaches that God, the beginning and end of all things, may be certainly known by the natural light of human reason, by means of created things.”

The accompanying canon declares:

“If anyone shall say that the one true God, our Creator and Lord, cannot be certainly known by the natural light of human reason through created things: let him be anathema.”

The official Latin text states that God can be certo cognosci — known with certainty — through created things by the natural light of human reason. An accessible English translation is available here: First Vatican Council — Dei Filius, English text

This teaching has considerable theological weight. The proposition that God's existence is naturally knowable with certainty is not simply a probable theological opinion. It belongs to the solemn teaching of the First Vatican Council.

The Council also carefully distinguishes reason from faith. Human reason can reach certain truths about God naturally. Other truths surpass man's natural intellectual powers and must therefore be revealed by God. Dei Filius explicitly teaches these two orders of knowledge.

What Sort of God?

The God whom Catholic philosophy reaches is not merely a powerful creature somewhere inside the universe.

Dei Filius, Chapter I, professes one true and living God who is Creator and Lord of heaven and earth, eternal, infinite, spiritual, immutable, absolutely simple, and truly distinct from the world.

This distinction matters. Classical Catholic theology does not propose that somewhere before the universe there existed an unusually powerful being who happened to manufacture it. Rather, God is the ultimate explanation of why finite things exist at all: the uncaused cause, necessary being and first source upon which every dependent reality ultimately depends.

Historical and Theological Evidence

St Thomas Aquinas: Can God's Existence Be Demonstrated?

St Thomas Aquinas deals explicitly with the question in the Summa Theologiae, First Part, Question 2.

He first asks whether God's existence is self-evident to us. His answer is nuanced: although God necessarily exists in Himself, His existence is not immediately self-evident to the human mind.

He then asks whether God's existence can be demonstrated. His answer is yes: we reason from effects known to us toward their ultimate cause.

Finally, in Summa Theologiae I, q. 2, a. 3, he gives what later came to be known as the Five Ways.

They are often badly reduced to slogans. Properly understood, they concern deep metaphysical features of reality.

1. From Change to a First Unchanged Source

The first argument begins with change.

For St Thomas, “motion” does not mean merely physical movement from one location to another. It includes change in the broader metaphysical sense: something that is potentially a certain way becoming actually that way.

A cold object can become hot.
An acorn can become an oak.
A person ignorant of a fact can come to know it.

Something potential does not actualise itself in precisely the same respect in which it is potential. What is merely potentially hot, for example, does not make itself actually hot simply because it has that potential.

The actualisation must ultimately depend upon something already actual.

Aquinas therefore reasons through ordered causes to a first source of actuality that does not itself require actualisation by another.

This is what classical Thomism calls the First Mover.

It is important not to misunderstand the argument. Aquinas is not merely saying:

“Everything moves; therefore at some remote moment billions of years ago there must have been a first push.”

His argument concerns the dependence of changing things here and now.

Even if the physical universe had existed through an indefinitely long temporal sequence, Aquinas held that its present dependence upon a first source of actuality would still require explanation.

2. From Efficient Causes to a First Cause

The second way begins from efficient causality.

We encounter things whose causal power is derivative. They produce effects because they themselves possess powers and existence which they did not give to themselves.

Aquinas denies that an essentially ordered series of causes can consist entirely of derivative causes with no primary source.

Consider a simple illustration: a stick moves a stone because a hand moves the stick. The stick possesses no independent power to initiate the motion in that example. Remove the principal cause and the instrumental causes explain nothing.

The philosophical point is not that every event must have an earlier event extending backwards until one reaches the oldest event.

Rather, derivative causal power ultimately requires a non-derivative source.

That first cause is not itself one more member of the dependent series.

3. From Contingency to Necessary Being

The third way begins from the distinction between contingent and necessary beings.

The things around us do not contain within themselves the sufficient reason for their own existence. They come into existence, change and cease to exist. Nothing about the nature of a tree, planet, animal or human being requires that this particular individual must exist.

They are therefore contingent.

But multiplying contingent things does not remove contingency. Ten dependent beings do not become self-explanatory simply because there are ten of them. Nor does an indefinitely large collection of contingent beings become metaphysically necessary merely through multiplication.

Ultimately, contingent existence requires a reality whose existence is not received from another — a necessary being.

Catholic philosophy identifies this ultimate necessary reality as God.

4. From Degrees of Perfection

Aquinas next reasons from gradations such as truth, goodness and nobility.

This is perhaps the most easily misunderstood of the Five Ways. He is not simply saying, “Some things are good, therefore a perfectly good being must exist.”

The argument rests upon the metaphysics of being and transcendental perfection developed in the Aristotelian-Thomistic tradition. Created perfections exist in finite and participated ways. They point toward a source in which perfection is possessed not derivatively but essentially.

This argument requires more philosophical preparation than the first three and should not be reduced to a popular slogan.

5. From Order and Finality

The fifth way begins from the directedness or regularity apparent in nature.

Natural things that lack intelligence nevertheless act in stable and intelligible ways toward characteristic effects. Acorns develop according to the nature of oak trees rather than randomly into fish or granite; natural powers have determinate ranges of operation.

Aquinas argues that this orientation of unintelligent nature toward determinate ends ultimately presupposes intelligence.

Again, this is not simply an argument from biological complexity of the modern “watchmaker” variety. It is an argument about final causality — the fact that natural powers are intrinsically ordered toward particular effects.

Consequently, the Thomistic argument is not abolished merely by discovering additional mechanisms through which natural processes operate.

A mechanism describes how one natural cause acts upon another. It does not, by itself, explain why there exists an ordered system of real causes with determinate powers in the first place.

The full text of Aquinas's treatment is available here: St Thomas Aquinas, Summa Theologiae I, q. 2

These Arguments Are Not “God of the Gaps”

A common misunderstanding says that belief in God exists only because earlier people lacked scientific explanations.

Lightning was once attributed to God; now electricity explains it.
Disease was attributed to God; now microorganisms can explain many diseases.
The formation of stars can be studied through astrophysics.
Biological development can be studied through genetics and other sciences.

Therefore, it is argued, God becomes less necessary as science advances.

But this misunderstands the classical Catholic argument. Aquinas is not attempting to insert God into places where science has not yet discovered a physical cause.

Suppose science gave a complete physical description of every measurable event in the universe. The philosophical question would remain:

Why does this entire system of contingent, changing, causally dependent reality exist and possess causal power at all?

Physics studies physical causes. Natural theology asks why there is any contingent physical reality capable of behaving according to intelligible principles.

These are different levels of explanation.

The Argument Does Not Depend upon the Big Bang

It is therefore unnecessary to make the existence of God depend upon contemporary cosmology.

A beginning of the physical universe may be philosophically or scientifically relevant, but the traditional Catholic demonstration of God does not require us first to prove that modern cosmological models describe an absolute beginning of all physical reality.

St Thomas himself did not believe that philosophy could demonstrate that the world had a temporal beginning. Creation in time was known by revelation.

Yet he believed God's existence was demonstrable by reason.

That fact alone shows that his argument cannot simply be:

“The universe began, therefore God caused the beginning.”

The deeper argument concerns the universe's ontological dependence — its dependence in being — whether its measurable history is ten billion years, a hundred billion years, or imagined as temporally beginningless.

The Roman Catechism

The Catechism of the Council of Trent, issued under Pope St Pius V, begins its treatment of the Creed with the profession:

“I believe in God, the Father Almighty, Maker of heaven and earth.”

It explains God as the supreme and most perfect good who created all things from nothing and continually preserves and governs what He created.

This is important because Catholic doctrine does not teach merely that God once caused the universe and then withdrew.

Creation involves radical dependence upon God.

The Roman Catechism teaches that created things do not possess existence independently of Him; they remain dependent upon His conserving power.

A reliable scan of the 1829 Donovan translation is available here: Catechism of the Council of Trent — 1829 scan

Pope Pius XII: Why So Many People Still Doubt

If God's existence can be known by reason, an obvious question follows: why do intelligent people disagree about it?

Pope Pius XII addresses an important part of the answer in Humani Generis of 12 August 1950.

He affirms the capacity of reason to reach genuine knowledge of God but explains that human beings do not reason in a vacuum. Imagination, intellectual habits, passions, prejudice, upbringing and the effects of fallen human nature can interfere with the easy attainment of religious and moral truth.

Consequently, divine revelation is morally necessary so that such truths can be known by all “readily with a firm certainty and with freedom from all error.”

This distinction prevents two opposite mistakes.

The Catholic Church does not teach that God's existence is inherently unknowable and must simply be believed without evidence.
Nor does she teach that every individual atheist who has not reached the correct conclusion must therefore be deliberately dishonest.

The doctrine concerns the objective capacity of human reason. The interior knowledge, obstacles, good faith and culpability of particular persons are separate questions and ultimately belong to God's judgment.

The full encyclical is available here: Pius XII, Humani Generis, 12 August 1950

Common Objections

“Who Created God?”

This objection usually begins with a misunderstanding of the argument.

The Catholic argument is not:

Everything has a cause.
Therefore the universe has a cause.
That cause is God.

If everything without exception required a cause, God would indeed require one.

But Aquinas does not say that everything has a cause. He argues that changing things require an actualising cause, that derivative causes require a primary cause, and that contingent beings require an ultimate necessary source.

God is not proposed as another contingent object requiring explanation.

He is precisely the non-derivative reality at which the explanatory regress terminates: the necessary source that does not receive existence from another.

To ask “Who created the uncreated Creator?” is therefore comparable to asking “What is north of the North Pole?” The question imports into the definition precisely the characteristic being denied.

The serious philosophical question is instead whether such a necessary reality actually follows from contingent reality.

Aquinas argues that it does.

“Why Can't the Universe Itself Be the Necessary Thing?”

This is a stronger objection.

Why posit God? Why not simply say that the universe exists necessarily?

The difficulty is that the universe we actually encounter consists of changing, composite and contingent realities.

Individual physical things come into existence and pass away. Their states could be otherwise. Their existence is not contained in their definitions.

Calling the total collection “the universe” does not automatically remove that dependence.

If every book in a library is borrowed, describing all the borrowed books collectively as “the library collection” does not make any of them unborrowed.

Likewise, assembling contingent realities into one conceptual totality does not by itself produce metaphysical necessity.

Aquinas's argument therefore proceeds from derivative being to that which possesses existence non-derivatively.

Whether every step of a particular philosophical demonstration has been formulated successfully remains open to philosophical analysis. But simply calling the universe a “brute fact” does not explain it; it terminates inquiry by declining to give an explanation.

“Hasn't Science Replaced God?”

No. Science has dramatically increased human knowledge of physical processes. Nothing in Catholic theology requires denying genuine discoveries concerning secondary causes.

If a scientist explains the mechanism by which rain forms, he has not disproved God.
If astrophysics explains stellar formation, it has not disproved God.
If biology discovers natural processes that account for particular features of organisms, it has not disproved God.

These discoveries explain relationships among created realities.

The argument for God concerns why any such realities, causal powers, laws, regularities and intelligible structures exist at all.

God and a physical mechanism are therefore not competing causes in the same category.

“If God Exists, Why Is There Evil?”

St Thomas himself presents this as the first objection in the very article in which he proves God's existence.

If God is infinitely good, the objection says, evil should not exist. Evil exists. Therefore God does not exist.

Aquinas answers that God's goodness is not contradicted merely by His permitting finite creatures to suffer defects or by His permitting free creatures to misuse their freedom.

Christian theology goes much further into the purposes for which evil may be permitted, but at the philosophical level the existence of evil would disprove God only if these propositions were established:

an infinitely good God could never have a morally sufficient reason to permit any evil;
evil exists;
therefore such a God cannot exist.

The crucial premise is the first.

It is not self-evident.

Indeed, human experience regularly shows that permitting a lesser evil can sometimes be compatible with wisdom and goodness when a sufficient good is involved — for example, painful surgery to preserve life.

This analogy does not solve every emotional or theological dimension of suffering. It does show that “evil exists” and “a good God exists” are not formally contradictory propositions.

The problem of evil deserves a separate article because Christianity makes further claims concerning original sin, freedom, providence, suffering, redemption and eternal life.

“But These Arguments Don't Prove Christianity”

Correct. And they are not intended to.

Natural theology establishes certain truths about God by reason.

It does not prove by itself that God is a Trinity.
It does not prove that Jesus of Nazareth is God incarnate.
It does not establish that Christ rose bodily from the dead.
It does not establish which religious body is the Church founded by Christ.

Those are subsequent questions.

This distinction is crucial to serious Catholic apologetics.

A person investigating Christianity should not be asked to accept the entire Catholic Faith merely because the existence of a first cause has been demonstrated.