St. Thomas Aquinas: The Angelic Doctor and the Synthesis of Faith and Reason

 Saint Thomas Aquinas (1225–1274) stands as one of the most influential thinkers in Western intellectual history. A Dominican friar, theologian, philosopher, and Doctor of the Church, he is often called the Angelic Doctor (Doctor Angelicus) for the sublime clarity and elevation of his thought, and the Common Doctor because his teachings became the foundational framework for Catholic theology. His masterwork, the Summa Theologica, remains one of the most comprehensive and systematic presentations of Christian doctrine ever written.

Early Life and Education

Born at Roccasecca in the Kingdom of Naples, Thomas was the youngest son of a noble family related to the Holy Roman Emperors. At age five he was sent to the Benedictine abbey of Monte Cassino, and later studied at the University of Naples, where he encountered the newly rediscovered works of Aristotle through Arab and Jewish commentators (especially Averroes and Maimonides). Against fierce family opposition—he was even imprisoned by his brothers for over a year—Thomas joined the Dominican Order in 1244.

He studied under Albertus Magnus (Albert the Great) in Paris and Cologne. Albert immediately recognized Thomas’s genius; legend says that when classmates mocked the silent, heavyset young man as “the Dumb Ox,” Albert replied, “This ox will one day fill the world with his bellowing.”

Philosophical and Theological Revolution

Medieval Europe in the 13th century faced a crisis: the full corpus of Aristotle—previously known only in fragments—had flooded in from Muslim Spain and Sicily. Many churchmen feared that Aristotle’s naturalistic, apparently non-Christian philosophy threatened revelation. Some condemned it outright (as in the 1210 and 1277 prohibitions at Paris).

Aquinas took the opposite approach: instead of rejecting Aristotle, he baptized him. He showed that reason and faith are not enemies but harmonious:

“Grace does not destroy nature but perfects it” (gratia non tollit naturam, sed perficit).

This principle became the cornerstone of his thought.

The Five Ways (Quinque Viae)

In the Summa Theologica (ST I-II, q. 2, a. 3), Aquinas offers his famous Five Ways to prove the existence of God—arguments still debated by philosophers today:

1. The Argument from Motion (change): Whatever is moved is moved by another; there must be a First Unmoved Mover—God.
2. The Argument from Efficient Causation: There cannot be an infinite regress of causes; there must be a First Uncaused Cause—God.
3. The Argument from Contingency: Contingent beings require a Necessary Being whose existence is not dependent on anything else—God.
4. The Argument from Degrees of Perfection: The existence of varying degrees of goodness, truth, beauty, etc., implies a maximum, a most perfect being—God.
5. The Teleological Argument: The orderly functioning of nature (like an arrow hitting its mark) implies a supreme intelligence directing it—God.

These are not “proofs” in the modern scientific sense, but rational demonstrations that the existence of God is philosophically demonstrable, not merely an article of faith.

Key Doctrines

• Being (Esse) and Essence: Aquinas’s metaphysics centers on the real distinction between essence (what a thing is) and existence (that it is). In everything except God, essence and existence are distinct; in God alone they are identical—He is ipsum esse subsistens (subsistent being itself).
• Natural Law: Moral truth is accessible to human reason. The first precept of natural law is “good is to be done and pursued, and evil avoided.” From this flow concrete norms (preservation of life, procreation and education of offspring, living in society, seeking truth about God).
• Faith and Reason: Neither contradicts the other. Philosophy serves theology as the handmaiden (ancilla theologiae) serves her mistress.
• Sacraments and Grace: Aquinas gave the classic formulation of the seven sacraments and the distinction between sanctifying grace, actual grace, and the virtues (theological and cardinal).

Major Works

• Summa contra Gentiles (1259–1265) – written partly for missionaries to Muslims, a more philosophically oriented defense of Christianity.
• Summa Theologica (1265–1273) – his unfinished masterpiece, intended as a complete handbook for theology students.
• Commentaries on Aristotle (especially On the Soul, Physics, Metaphysics, and Nicomachean Ethics), which profoundly shaped later Western philosophy.

Death and Legacy

In 1274, while traveling to the Second Council of Lyon, Thomas experienced a profound mystical vision during Mass. Afterward he declared that all he had written seemed like “straw” compared to what had been revealed to him. He stopped writing. Three months later, on March 7, 1274, he died at the Cistercian abbey of Fossanova, aged 49.

He was canonized in 1323, declared a Doctor of the Church in 1567, and in 1879 Pope Leo XIII’s encyclical Aeterni Patris made Thomism the official philosophical and theological system of the Catholic Church—a status it largely retained until Vatican II.

Even today, Thomistic philosophy remains vibrant in Catholic thought (John Paul II’s 1998 encyclical Fides et Ratio heavily cites Aquinas), and his arguments continue to be engaged by analytic philosophers of religion (e.g., Elizabeth Anscombe, Peter Geach, Eleonore Stump, Edward Feser).

In an age that often pits science against religion, or faith against reason, Thomas Aquinas still stands as the supreme witness that the human mind, when rightly ordered, inevitably leads toward the God who is Truth itself.

Here is a detailed, step-by-step explanation of St. Thomas Aquinas’s Five Ways (Quinque Viae) as they appear in the Summa Theologica (ST II-I, q. 2, a. 3). Aquinas presents them not as emotional appeals or probabilistic arguments, but as strict philosophical demonstrations starting from undeniable facts of experience and proceeding (mostly via Aristotle’s principle of non-contradiction and avoidance of infinite regress) to the existence of God.

1. The First Way: The Argument from Motion (Change)

Latin name: Ex motu Core observation: Some things in the world are changing (in Aristotle’s wide sense of “motion” = any actuality of a potentiality: local motion, quantitative change, qualitative change, and substantial change).

1. Whatever is being changed is being changed by something else (a thing cannot actually change itself; it must be actualized by another already-actual mover).
2. This produces a series of simultaneous movers: fire is made hot by something already hot, the stick is moved by the hand, etc.
3. This hierarchical series cannot go on to infinity, because then there would be no first mover, and consequently no intermediate movers, and thus no motion now (remove the first cause and the whole series collapses).
4. Therefore there must be a First Unmoved Mover (primum movens immobile) that is itself pure act (actus purus), with no potentiality — otherwise it would need to be moved by another.
5. This everyone understands to be God.

Key point: This is not about the beginning of the universe (cosmological argument in the modern sense), but about what is keeping things in change right now.

2. The Second Way: The Argument from Efficient Causation

Latin name: Ex causa efficienti Core observation: We see an ordered series of efficient causes in the world (A causes B, B causes C, etc.).

1. Nothing can be the efficient cause of itself (that would require it to exist before it exists — impossible).
2. In any ordered series of causes happening now (per se, not per accidens), the later members depend on the earlier ones.
3. It is impossible to have an infinite regress in such an essentially ordered (hierarchical) series, because if you remove the first cause, all subsequent causation vanishes.
4. Therefore there must be a First Efficient Cause that is itself uncaused (causa efficiens prima, incausata).
5. This everyone calls God.

Important distinction: Aquinas is not talking about a temporal series stretching back in time (like “who made your parents? grandparents? …”). He means a simultaneous, hierarchical series (e.g., the sculptor moves the chisel that moves the stone).

3. The Third Way: The Argument from Contingency (Possibility and Necessity)

Latin name: Ex possibili et necessario This is the longest and most misunderstood of the Five Ways. It has two phases.

Phase 1 – Contingency

1. We find things that are contingent (they come into being and pass away; they might not have existed).
2. Everything that is contingent has a time when it does not exist.
3. If everything were contingent, then at one time nothing existed.
4. If at one time nothing existed, then nothing would exist now (nothing comes from nothing).
5. But things do exist now → therefore not everything is contingent.

Phase 2 – Necessary Being 6. Therefore there must be something necessary (whose non-existence is impossible). 7. Every necessary being either has its necessity caused by another or not. 8. There cannot be an infinite regress of necessary beings each deriving necessity from another. 9. Therefore there must be a being that is necessary in itself (per se necessarium), not receiving necessity from another — its essence is its very existence. 10. This is what everyone calls God.

This argument is often seen as Aquinas’s version of the Leibnizian “Why is there something rather than nothing?” question.

4. The Fourth Way: The Argument from Degrees of Perfection (Gradation)

Latin name: Ex gradibus perfectionis Core observation: We observe that things have perfections (goodness, truth, beauty, being, nobility, etc.) to greater or lesser degrees.

1. Things are more or less good, true, noble, etc., only by comparison to a maximum (just as “hotter” implies something hottest).
2. The maximum in any genus is the cause of all in that genus (Aristotle’s principle: the hottest thing causes all other heat).
3. Therefore there must be something that is the cause of being, goodness, and every perfection in all other things — something that is maximum in being and perfection.
4. This maximum is not merely the best in a series; it is that than which nothing greater can be thought, and it must itself be uncaused and unlimited (otherwise something greater could be conceived).
5. This everyone understands to be God.

Note: This is not the same as Anselm’s ontological argument. Aquinas starts from real gradations observed in the world, not from a mere concept.

5. The Fifth Way: The Teleological Argument (Governance of the World)

Latin name: Ex gubernatione rerum Core observation: Natural (non-intelligent) things act for ends and do so regularly.

1. Whenever something acts for an end, the direction toward that end must come from intelligence (an arrow reaches the target because an archer aimed it).
2. Non-intelligent things (plants, atoms, planets, etc.) cannot direct themselves toward ends; they have no knowledge.
3. Yet they achieve their ends consistently and beneficially (acorns become oaks, eyes are for seeing, etc.).
4. Therefore their directedness must come from some intelligence outside themselves.
5. Therefore there exists an intelligent being by whom all natural things are directed to their ends.
6. This we call God.

This is not Paley’s watchmaker argument (which is about complexity). It is about final causality in nature itself — the fact that things lacking cognition nevertheless reliably act “as if” they had a purpose.

Summary Table of the Five Ways

Way	Starting Point	Key Principle	Conclusion
1	Motion/change	Nothing moves itself	Unmoved Mover (Pure Act)
2	Efficient causation	No infinite hierarchical regress	Uncaused First Cause
3	Contingency/necessity	Something must explain why anything exists at all	Necessary Being (Esse itself)
4	Degrees of perfection	Maximum is cause of the genus	Supreme Good/Being
5	Order and finality in nature	Non-cognitive things act for ends	Supreme Intelligence

These five arguments converge on the same reality — a single being who is unmoved, uncaused, necessary, maximally perfect, and intelligent — whom Aquinas identifies with the God of Abraham, Moses, and Jesus Christ. For Aquinas, philosophy reaches the threshold of the living God; revelation then tells us who this God personally is.

Anselm’s Ontological Argument vs. Aquinas’s Five Ways: A Side-by-Side Comparison

Aspect	St. Anselm (Proslogion, ch. 2–4, 1078) → Ontological Argument	St. Thomas Aquinas (Summa Theologica I-II, q. 2, a. 3, 1265–1273) → Five Ways
Type of argument	Purely a priori(from the definition/concept alone; no appeal to sensory experience)	A posteriori (all five begin from undeniable facts of experience: change, causation, contingency, degrees, finality)
Starting point	In the intellect only: the concept/definition of God as “that than which nothing greater can be conceived” (id quo maius cogitari nequit)	In the real world: things we actually observe (motion, causes, contingent beings, gradations, ordered activity of non-intelligent things)
Key move	1. Even the Fool (Psalm 14:1) understands the definition of God. 2. To exist in reality is greater than to exist only in the intellect. 3. Therefore, if “that than which nothing greater can be conceived” existed only in the intellect, a greater being (one that also exists in reality) could be conceived. 4. But this is contradictory. ∴ God must exist in reality.	Each Way begins from a different observable feature of the world and shows (using Aristotelian principles) that an infinite regress is impossible or absurd, so there must be a First Unmoved Mover, Uncaused Cause, Necessary Being, Maximum, or Intelligent Orderer.
Does Aquinas accept Anselm’s argument?	No. Aquinas explicitly rejects it twice: • Summa Theologica I, q. 2, a. 1, ad 2 • De Veritate q. 10, a. 12 • ScG I, ch. 10–11 His reason: From the mere concept or definition of God we cannot conclude that God actually exists outside the mind, because the human intellect can conceive things that do not exist in reality (e.g., a golden mountain).	Yes (his own arguments). He insists that God’s existence is not self-evident (per se notum) to us in this life; it must be demonstrated from effects (ex effectibus).
Role of God’s essence	The argument hinges entirely on the essence/definition: existence belongs analytically to the concept of the most perfect being.	Essence and existence are only identical in God, but we discover this conclusion at the end of the argument, not at the beginning. The Five Ways first prove there is a being whose essence is existence (ipsum esse subsistens); they do not start by assuming it.
Vulnerability to Kant’s critique	Extremely vulnerable. Kant’s famous objection (“existence is not a real predicate”) directly destroys Anselm’s key premise that real existence adds perfection to the concept.	Largely unaffected. Aquinas is not treating existence as a property added to a concept; he is arguing from real causal series and real contingency in the world to a being that must exist to explain those realities.
Relation to the Fourth Way	Superficial similarity: both speak of a being “than which nothing greater can be conceived.” Crucial difference: Anselm starts with the concept and deduces existence; Aquinas starts with real degrees of perfection observed in creatures and argues to a transcendent maximum that must actually exist as their cause.	The Fourth Way looks like a distant cousin, but it is still a posteriori and causal, not purely conceptual.
Historical influence	Enormous in later medieval philosophy (rediscovered and refined by Descartes, Leibniz, Gödel, Plantinga’s modal version, etc.).	Became the standard Catholic “proofs” for centuries (Council of Trent, Vatican I, Catechism 1992 §31–36). Still the most commonly taught arguments in Thomistic circles.
Aquinas’s own summary of his objection to Anselm	“Even if one grants that the word ‘God’ signifies by its meaning that than which a greater cannot be thought, it does not follow that there exists in reality something than which a greater cannot be thought… From the fact that the mind thinks of something when it understands the meaning of the word, it does not follow that the thing exists except in the intellect.” (ScG I, 11)	—

Bottom-Line Difference in One Sentence

• Anselm tries to move from the pure concept of God to His real existence in one logical leap (“I have the idea of a perfect being → a perfect being must exist”).
• Aquinas refuses that leap and instead takes five separate paths from the observable world back to a First Cause whose very nature turns out to be existence itself.

That is why Aquinas, while admiring Anselm’s piety and ingenuity, judged the ontological argument philosophically invalid and replaced it with the empirical, causal demonstrations of the Five Ways.

Kant’s Critique of the Ontological Argument

(Immanuel Kant, Critique of Pure Reason (1781/1787), Transcendental Dialectic, Book II, Chapter III, Section 4: “The Impossibility of an Ontological Proof of the Existence of God”)

Kant’s objection is widely regarded as the single most devastating blow ever delivered to Anselm’s argument (and to all later purely conceptual versions: Descartes, Leibniz, etc.). It is short, brutal, and almost universally accepted by modern philosophers as fatal.

The Core Thesis in Kant’s Own Words

“Being [existence] is obviously not a real predicate, that is, a concept of something which could be added to the concept of a thing. … If, then, I try to conceive a being, as the highest reality … I do not have to add existence to it. … Whatever, therefore, and however much, our concept of an object may contain, we must go outside it if we are to ascribe existence to the object.” (A599/B627–A600/B628)

Translated into plain language: “Existence is not a perfection, not a property, not a feature you can add to a concept to make it ‘better.’ Saying that something exists does not enrich the concept of the thing at all.”

Step-by-Step Breakdown of Kant’s Argument

1. Real vs. Logical (Analytical) Predicates

   • A real predicate adds new content or determination to the concept (e.g., “red,” “triangular,” “wise,” “omnipotent”).
   • A logical predicate is just the copula “is” that connects subject and predicate in a judgment (e.g., “The triangle is three-sided” is analytic; the “is” does not add a new property).
   • Kant’s claim: existence is never a real predicate. When I say “God exists” or “This table exists,” I am not adding a new feature to the concept of God or the table. I am only positing that the entire concept (with all its predicates) is instantiated in reality.

2. The Famous “100 Thalers” Illustration

   “A hundred real thalers do not contain the least coin more than a hundred possible thalers. … My financial position is, however, affected very differently by a hundred real thalers than by the mere concept of them.” (A599/B627)

   • The concept of 100 thalers includes: round, silver, stamped by the Prussian mint, worth X amount of goods, etc.
   • When the 100 thalers actually exist in my pocket, the concept is exactly the same. Nothing has been added to the concept itself.
   • What has changed is only the relation of the concept to reality: the object corresponding to the concept is now instantiated.
   • Therefore, existence is not a property that enriches or perfects the concept.

3. Application to Anselm/Descartes Anselm and Descartes claim:

   • God = the most perfect being (ens realissimum).
   • Necessary existence (or actual existence) is itself a perfection.
   • Therefore, the most perfect being must possess the perfection of existence; otherwise a greater being (one that exists) could be conceived.

   Kant’s reply:

   • Even if we grant that “necessary existence” belongs to the concept of God by definition (analytic judgment), that only tells us: if God exists, then He exists necessarily.
   • It tells us absolutely nothing about whether God actually exists.
   • To move from “If X exists, then X exists necessarily” to “X actually exists” is to smuggle in existence as a real predicate—which it is not.

4. The Illegitimate Leap from Logical to Real Possibility

   • Anselm says: “If the being than which nothing greater can be conceived existed only in the intellect, then a greater could be conceived (one that also exists in reality).”
   • Kant: This assumes that the concept “that than which nothing greater can be conceived” is a real possibility (i.e., contains no hidden contradiction).
   • But we can form concepts that are logically consistent yet refer to nothing real (e.g., a perfect island, a necessarily existing unicorn). Logical non-contradiction does not guarantee real possibility.
   • Therefore the entire argument collapses before it even starts.

5. Summary in One Sentence

   “You can no more define something into existence than you can define 100 thalers into your wallet.”

Why Kant’s Critique Does Not Touch Aquinas’s Five Way

Kant’s Target	Anselm / Descartes / Ontological Argument	Aquinas’s Five Ways
Treats existence as a real predicate that can be included in a concept?	Yes (explicitly)	No
Starts from a concept/definition of God?	Yes (entirely a priori)	No (all start from empirical facts)
Claims God’s essence includes existence analytically?	Yes	No (concludes only at the end that God’s essence = existence)
Vulnerable to “existence is not a predicate”?	Completely fatal	Unaffected (Aquinas is arguing from real causal series to a being that must exist to terminate them)

Kant himself explicitly says that his critique only destroys the ontological proof, not the cosmological or physico-theological (teleological) proofs—though he then goes on to attack those on other grounds (the cosmological inevitably slips into the ontological, etc.). Thomists reply that Aquinas’s versions of the cosmological and teleological arguments do not make that illicit slide, precisely because they never treat existence as a predicate added to a concept.

Lasting Impact

After Kant, virtually no major philosopher (except some theistic modal logicians like Plantinga and Gödel in the 20th century) has tried to defend the pure ontological argument in its original Anselmian/Descartesian form. The consensus is: Kant killed it.