Thomas Aquinas: A Critical Evaluation of His Theology, Philosophy, and Its Relationship to Biblical Authority

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Thomas Aquinas (1225–1274 C.E.), the Dominican friar and medieval theologian, is considered one of the most influential figures in the history of Western theology and philosophy. As the central figure of High Scholasticism, Aquinas attempted a grand synthesis of Christian doctrine and Aristotelian philosophy. His chief theological work, Summa Theologica, aimed to systematically present the entire body of Christian doctrine as it was understood within the medieval Roman Catholic Church, using Aristotelian categories and methods.

While Aquinas is often credited with defending certain orthodox Christian doctrines and with being a meticulous thinker, a sober and biblical analysis must carefully distinguish between his use of biblical truth and his use of extrabiblical philosophy. A high view of Scripture—one that affirms its sufficiency, clarity, and inerrancy—requires a critical assessment of Aquinas’s teachings in light of the Bible. While he made some contributions to apologetics and natural theology, his over-reliance on Aristotelian philosophy, speculative metaphysics, and ecclesiastical tradition introduces serious theological errors and distortions that are incompatible with the historical-grammatical interpretation of Scripture.

This article examines Aquinas’s background, his philosophical system, his theological doctrines, and his long-term impact, with a particular focus on where his thinking aligns—or fails to align—with the inerrant Word of God.

Background and Education

Thomas Aquinas was born in 1225 C.E. in Roccasecca, near Aquino in the Kingdom of Sicily. He entered the Dominican order in 1244 and studied at the University of Paris and under Albertus Magnus in Cologne. Aquinas was deeply immersed in both biblical studies and the newly rediscovered writings of Aristotle, which were becoming available through Arabic and Jewish intermediaries.

He spent much of his career as a professor and writer, producing theological commentaries, disputations, and his monumental Summa Theologica—a systematic synthesis of Christian doctrine shaped by Aristotelian categories. He died in 1274 en route to the Second Council of Lyon and was canonized in 1323.

Philosophical Foundations: Aristotle and the Scholastic Method

Aquinas’s entire theological system rests on a synthesis between Christian doctrine and Aristotelian philosophy. He adopted Aristotle’s metaphysical framework, including the distinction between act and potency, substance and accident, form and matter, and the four causes (material, formal, efficient, and final).

Illustration of Scholasticism in the High Middle Ages, capturing the vibrant fusion of faith, logic, and academic rigor within cathedral schools and medieval universities.

Aquinas believed that reason and revelation are two distinct yet complementary sources of knowledge. He posited a “twofold truth”: some truths (e.g., the Trinity, the Incarnation) can only be known through special revelation, while others (e.g., the existence of God, natural law) can be discovered through human reason and observation of the natural world.

While Aquinas affirmed the ultimate authority of Scripture, his method consistently elevated philosophical reasoning, particularly through dialectical disputation, in a manner that often reinterpreted or subordinated biblical truths to Greek metaphysical categories. This approach, foundational to scholasticism, opened the door to numerous theological distortions.

The Five Ways: Aquinas’s Proofs for the Existence of God

Aquinas is perhaps best known in apologetic circles for his quinque viae—the Five Ways to prove the existence of God. These arguments are:

The Argument from Motion
The Argument from Efficient Cause
The Argument from Contingency
The Argument from Degrees of Perfection
The Teleological Argument (Argument from Final Cause)

Each of these attempts to demonstrate, through empirical observation and Aristotelian causality, that there must be a First Cause or Prime Mover—namely, God.

While these arguments are intended to point to the existence of a necessary, eternal, and immutable being, they are grounded in natural reason rather than divine revelation. Scripture itself never argues for God’s existence philosophically. Rather, it presupposes it. Genesis 1:1 states, “In the beginning God created the heavens and the earth,” with no philosophical preliminaries. Psalm 14:1 declares, “The fool has said in his heart, ‘There is no God.’”

Romans 1:19–20 confirms that God’s invisible attributes—His eternal power and divine nature—are evident in creation, but it attributes this knowledge to general revelation, not to metaphysical speculation. Aquinas’s philosophical arguments, while logical in form, fall short of the biblical method, which calls for faith based on God’s self-revelation, not rational construction.

Aquinas’s Doctrine of God

Aquinas affirmed the classical attributes of God: simplicity, immutability, eternality, omniscience, omnipotence, and perfect goodness. However, he defined many of these attributes through Aristotelian metaphysical concepts.

For example, divine simplicity in Aquinas’s thought means that God has no parts, no composition, and no potentiality—He is pure act (actus purus). While the Bible teaches that God is unchanging (Malachi 3:6) and not composed (John 4:24, “God is spirit”), Aquinas’s metaphysical formulation moves beyond Scripture and ventures into speculative definitions not derived from exegesis.

Furthermore, Aquinas’s conception of God is so shaped by metaphysical abstraction that the biblical portrayal of a personal, covenantal, relational God is sometimes overshadowed. The God of Scripture reveals Himself in words, acts in history, feels compassion, and enters into covenant. Aquinas’s emphasis on the unmoved mover can drift toward a philosophical deity more in line with Aristotle than with the God of Abraham, Isaac, and Jacob.

The Doctrine of Analogy: Language About God

Aquinas rejected both univocal and equivocal language about God, advocating instead for the analogia entis—an analogy of being. According to this doctrine, we can speak truthfully about God only by analogy; our words do not mean the same thing when applied to God and to creatures but share a proportional similarity.

This leads to ambiguity in theological discourse. Biblical revelation is verbal, propositional, and precise. God communicates using human language so that He may be clearly understood (Deuteronomy 29:29; 2 Timothy 3:16). While it is true that God is infinitely greater than human comprehension (Isaiah 55:8–9), Scripture never implies that theological language is merely analogical or proportionally similar. When God says He is holy, just, or good, He means what those terms normally signify in a literal context, albeit in infinite measure.

Aquinas’s analogical view, though well-intentioned, risks undermining the clarity of Scripture by introducing philosophical abstraction into God’s self-disclosure.

Christology and the Atonement

Aquinas’s Christology was generally orthodox, affirming the full divinity and full humanity of Christ, the virgin birth, the hypostatic union, and the bodily resurrection. However, in explaining the atonement, Aquinas leaned on the satisfaction theory, building upon Anselm’s Cur Deus Homo. According to Aquinas, Christ’s death was necessary to satisfy the demands of divine justice and restore honor to God.

While there is a biblical basis for satisfaction (Isaiah 53:11; Romans 3:25–26), Aquinas’s treatment often fails to capture the full biblical picture of substitutionary atonement. The emphasis on satisfying God’s honor reflects medieval feudal notions more than the sacrificial system of the Old Testament, which pointed toward Christ’s vicarious, substitutionary death (Hebrews 9:22–28; 1 Peter 2:24).

The satisfaction model in Aquinas also blends with merit-based soteriology, which undermines the sufficiency of grace and the completed work of Christ on the cross (John 19:30).

Soteriology and Justification

Perhaps one of the most critical theological errors in Aquinas’s system is his doctrine of justification. He did not teach justification by faith alone but by a process involving the infusion of grace, cooperation with that grace, and eventual attainment of justification through sacramental participation and good works.

Aquinas wrote, “Justification is the movement whereby the soul is moved from the state of sin to the state of justice” (Summa Theologica, I-II, Q113). This process includes contrition, confession, and the infusion of sanctifying grace, which enables the believer to perform meritorious works.

This sharply contradicts the biblical teaching of justification by faith alone (sola fide) apart from works. Romans 3:28 states, “For we maintain that a person is justified by faith apart from the works of the law.” Ephesians 2:8–9 affirms, “For by grace you have been saved through faith… not as a result of works, so that no one may boast.”

Aquinas’s soteriology laid the groundwork for the sacramental system of Roman Catholicism, which the Reformers rightly rejected as unbiblical and contrary to the doctrine of grace.

Aquinas’s Use of Scripture

While Aquinas quoted Scripture frequently and often in Latin from the Vulgate, his method was not governed by the historical-grammatical interpretation. Instead, he frequently employed the fourfold method of interpretation: literal, allegorical, moral, and anagogical. This hermeneutic approach, derived from patristic tradition, allows for allegorical and mystical meanings not grounded in the original context of the text.

This method diverges from the literal, objective, grammatical-historical method commanded by Scripture itself (Nehemiah 8:8; Luke 24:27; Acts 17:2–3). Scripture interprets itself, and its meaning is rooted in the original intent of the author as guided by the Holy Spirit.

Thus, despite Aquinas’s extensive engagement with biblical texts, his interpretive method allowed for speculative theology that was not rooted in the plain sense of Scripture.

Conclusion

Thomas Aquinas remains a monumental figure in the history of Christian thought. His philosophical rigor, systematizing intellect, and devotion to the idea of theological coherence are noteworthy. However, his theological system is deeply compromised by its reliance on Aristotelian metaphysics, its speculative nature, and its departure from the sufficiency and clarity of Scripture.

Aquinas’s doctrines of justification, analogy, and speculative theology are inconsistent with a biblical theology grounded solely in God’s inspired Word. His contributions to apologetics and philosophical theology must be evaluated critically and biblically, not accepted uncritically based on ecclesiastical authority or intellectual reputation.

A truly evangelical theology must reject the philosophical method of Aquinas where it supersedes Scripture and instead affirm the historical-grammatical method, sola scriptura, and the absolute sufficiency of divine revelation as the only foundation for sound doctrine.

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About the Author

EDWARD D. ANDREWS (AS in Criminal Justice, BS in Religion, MA in Biblical Studies, and MDiv in Theology) is CEO and President of Christian Publishing House. He has authored over 220+ books. In addition, Andrews is the Chief Translator of the Updated American Standard Version (UASV).