Christian Thinkers 101: A Crash Course on St. Thomas Aquinas

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Thomas Aquinas’ system of thought was declared the official philosophy of the Roman Catholic Church, but what exactly did he believe and what else did he contribute to Christianity? Here’s your crash course on the life and accomplishments of St. Thomas Aquinas—and why he still matters today.

Who Was St. Thomas?

St. Thomas Aquinas (1225–1274) was born in a castle near Naples, Italy, in the High Middle Ages. The priests and monks of the Benedictine order within the Catholic Church educated him. Though his parents opposed him becoming a priest, he subsequently joined the Dominican order. While some of his fellow students called him “the dumb ox” as a youth, Thomas may have been the most intelligent Christian in history. For accomplishments within a lifespan that was just short of 50 years, he was honored as the most important philosopher and theologian within the entire Roman Catholic tradition. Thomas was a philosophical and theological genius, but still amazingly humble. There is a story that toward the end of his life, Thomas experienced a mystical vision that made him view everything he had written as “straw worthy to be burned.” Now that must have been an incredible vision!

What Did St. Thomas Write?

Though he was a prolific author and wrote commentaries on biblical, theological, and philosophical topics, Thomas’ two most important apologetics-related books are Summa Theologica and Summa Contra Gentiles. In the first, he uses Aristotelian philosophy as a framework for explaining and defending Christian theism. In the second, he defends Catholic Christianity in light of the Greco-Arabic (Islamic) worldview challenge.



What Did St. Thomas Believe?

Christians of various traditions continue to utilize several of St. Thomas Aquinas’ apologetic arguments. Perhaps his three most important ideas or arguments for historic Christianity are the following:

  1. Thomas devised five arguments—known as the Five Ways—for the existence of God: motion, first cause, contingency, perfection, and teleology. Christian philosopher and evangelical Thomist Norman Geisler summarizes Thomas’ Argument from Contingent Beings thusly: (a) some things exist but can not exist (i.e. possible beings); (b) and something has always existed; (c) but possible beings do not ground themselves; (d) therefore, there must be a necessary being.1
  2. Thomas believed that faith and reason were compatible. While natural reason alone is insufficient to discover the truths of divine revelation (Trinity, Incarnation, etc.), the divinely revealed truths themselves are not contrary to natural reason.
  3. Thomas maintained that language about God is to be understood analogically (both like and unlike human applications). For example, when the Bible speaks of God as “Father,” is that term being used univocally (same as a human father), equivocally (different from a human father), or analogically (both like and unlike a human father)?

Why Does St. Thomas Matter Today?

St. Thomas was criticized by some for using Aristotelian philosophy to explain the Christian worldview (in negative terms “Christianizing Aristotle’s God”). But, while a number of Aristotle’s views are in clear conflict with Christian theism, Christians of various traditions think Thomas’ synthesis was masterful. “Doctor Angelicus,” as he was called, was the greatest Christian thinker of the Medieval (scholastic) period. His system of thought, known as “Thomism,” was declared by Pope Leo XIII to be the official philosophy of the Roman Catholic Church. Canonized as a saint in 1323, Thomas Aquinas was truly one of the greatest philosophers and theologians of all time.

Evangelicals show a Thomistic influence when they appeal to formal arguments to attempt to support God’s existence and when they appeal to analogies to explain human language about God. It is not just Catholics who have been influenced by St. Thomas’ incredible mind.

Other articles in the Christian Thinkers 101 series: St. Augustine; C. S. Lewis; Blaise Pascal; St. Anselm; St. Athanasius

Reflections: Your Turn

Given Thomas Aquinas’ famous five proofs for the existence of God, what do you consider to be the best argument for the God of Christian theism?


  1. Norman Geisler, Thomas Aquinas: An Evangelical Appraisal (Grand Rapids: Baker, 1991), 120.


  • For an introduction to his work, see A First Glance at St. Thomas Aquinas: A Handbook for Peeping Thomists by Ralph McInerny.
  • To begin reading Thomas’ writings, see Aquinas’s Shorter Summa: St. Thomas Aquinas’s Own Concise Version of His Summa Theologica.
  • For analysis of St. Thomas Aquinas’ life and thoughts, see A History of Apologetics by Avery Dulles.
  • For a Protestant perspective on Aquinas and his work, see Thomas Aquinas: An Evangelical Appraisal by Norman L. Geisler.

  One thought on “Christian Thinkers 101: A Crash Course on St. Thomas Aquinas

  1. May 31, 2016 at 7:34 am

    Aquinas is so hugely influential even in Protestant circles. I think his most important contribution is from his study of being from an Aristotelian perspective. Whether I agree or not it is formidable and has made me think about it for years.

    I think Edward Feser’s look at the Five Ways in his book Aquinas made me rethink how powerful they were. Each has it’s own force and is intricately linked to Aquinas’s ontology. I think that his version of the teleological argument is quite powerful. They’re all stein though. I hope to speak with him at length in the New Creation.

    Thanks for this post!

    • May 31, 2016 at 11:14 am

      Hello, J.W.

      I noticed recently that the debate about whether to view God as a Being or the ground of Being has sparked some controversy among Christian theistic philosophers (i.e., Hart [EO], Feser [RC], Craig [Prot]).

      I appreciate the Five Ways and I think Thomas had a very strong view of Scripture’s authority as well as the absolute necessity of grace in salvation.

      One of my friends calls him the smartest Christian to ever live.

      Best regards.

      Ken Samples

  2. May 31, 2016 at 7:34 am

    When I say all stein I mean all strong. Commenting from phone is not easy.

  3. markgoddard
    May 31, 2016 at 11:17 am

    Ken, It would be great to hear some interaction with those who are critical of Thomism from a Reformed perspective.

    • May 31, 2016 at 1:31 pm

      Hello, Mark.

      Protestants have genuine and significant differences with Catholicism, but evangelicals can still learn a lot from St. Thomas Aquinas. Most evangelicals I’ve encountered know very little about any of the great Catholic philosophers-theologians. So the purpose of my Christian Thinkers 101 series is to provide them with a beginners guide to a variety of Christendom’s best thinkers (Catholic, Orthodox, and Protestant).

      Two Reformed authors that provide a thoughtful and measured critique of Thomism are Ronald Nash and John Frame.

      Best regards.

      Ken Samples

  4. May 31, 2016 at 11:59 am

    It’s hard to pick out one of Aquinas’ Five Ways as the best, since the cores of his Arguments overlap and link among themselves, pointing to one self-existent perfect and purposeful source of all we are and experience. There would be nothing without God, and there must be God because that is what He is. He is to be. Only this eternal incomprehensible God revealed in the Bible matches that reality, and thus the Bible provides our only way to Him (which is not a human way).

    The atheists who argue against the Five Ways can do so only by first presupposing one of two impossibilities: an inanimate energy improved itself; or a god has limits and is subject to another authority.

    • May 31, 2016 at 1:34 pm


      Thank you for your thoughtful philosophical and apologetics-related comments.

      Best regards.

      Ken Samples

  5. T. Fry
    June 8, 2016 at 8:05 pm

    I’m a huge Geisler fan, and so my interest and study of apologetics is heavily influenced by Aquinas even though I’ve never read his works directly. In particular, Geisler reviews the 4 classic arguments in his book Christian Apologetics: the Cosmological, Teleological, Axiological, and Ontological. The first three were straight forward and not particularly new when I read them, but the Ontological argument, is extremely powerful when combined with the first three. It remains mind-blowing to me nearly 20 years after I first read it.

    • June 8, 2016 at 9:20 pm

      Hello, T.

      Thanks for your comments.

      I’ve learned a lot from Norm Geisler as well. He is a Protestant Thomist.

      The traditional arguments for God’s existence are very powerful.

      Best regards in Christ.

      Ken Samples

    • June 20, 2016 at 2:49 pm

      Thank you, Jaime.

      Best regards.

      Ken Samples

  6. Mardo Jimenez
    February 21, 2017 at 12:46 pm

    It will be very interesting to compare Aquina’s arguments with Anselm.
    Thank you for your valuable post!
    Thank you also for the good comments. I learn from you all.

    • February 21, 2017 at 1:03 pm

      Thank you, Mardo.

      Best regards.

      Ken Samples

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