Are Faith and Reason Compatible?

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There’s a famous quote from Tertullian, one of the earliest Christian thinkers, about the relationship between faith and reason. (“Reason” being rationality or critical thinking.)

You may not have heard of him, but Tertullian - according to ChaptGPT - was born in Roman North Africa around the year 155 AD. He wrote at a time when Christianity was becoming increasingly distinct from Judaism, and his writings often reflect the growing separation between Christians and Jews in the second and third centuries.

Among his famous quote is, “What has Athens to do with Jerusalem?”

Relevant Today

Athens symbolizes Greek philosophy, human reason, and speculative inquiry and Jerusalem symbolizes divine revelation, faith, and the Christian gospel. Tertullian warned Christians not to let philosophical systems override or distort the truths revealed by Christ, a warning that is relevant today.

Subsequent Christian writers, however, steered the western church in another direction. Thinkers such as Justin Martyr, Augustine of Hippo, and especially Thomas Aquinas, argued that Athens and Jerusalem can be allies rather than enemies, that reason can help clarify, defend, and deepen what is known through faith.

Justin Martyr (c. AD 100–165) was one of the earliest and most influential Christian thinkers after the apostles. He is known as an early church father who defended Christianity through reasoned argument. He was executed in Rome for his faith.

Rendition of Justin Martyr
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He argued that Greek philosophers had grasped partial truths through reason and that any truth discovered by philosophers ultimately comes from God. He famously suggested that philosophers such as Socrates were, in a sense, Christians before Christ because they followed reason wherever it led.

Augustine of Hippo (354–430) and Thomas Aquinas (1225-1274) backed Justin’s view. Augustine wrote that Christians could borrow insights from pagan philosophy, especially Platonism, while rejecting what contradicted revelation. Aquinas’ view is often summarized as: "Believe in order to understand; understand in order to believe."

So, why should this matter to people searching for God?

Because we often let one get in the way of the other. For people who have not embraced faith, it is usually reason getting in the way of faith. In other words, they see faith as irrational. But the inability to scientifically prove doctrines of faith – including the existence of God – doesn’t mean faith is irrational.

The Catholic Church’s view (and I believe it is one shared by at least the major Christian denominations) is that “irrational” would mean believing contrary to reason or evidence. But there are good reasons for belief even if they are not scientifically demonstrable.

I believe the reasons, or “proofs,” are at least as credible as evidence presented in a court of law, starting with the witness of millions of believers through the ages. And the existence of God, I believe, is demonstrable through the writings of many philosophers and theologians – such as Aquinas – but also through an open-minded view of science.

The Beginning?

The “big bang” (Georges Lemaître, a Belgian Catholic priest, mathematician, and physicist, in 1927 proposed the theory that became the foundation of the Big Bang theory), for instance, is sometimes identified at the “beginning” of all that exists but how did the basis for the theory, the “extremely dense, hot initial state,” come to be?

I think the idea of God as “first cause” is believable and rational. And once you get past that question, the rationality of God’s care for and love of humans, and his intervention in the world through revelation (the Bible) and particularly in his Incarnation in Jesus, is a lot easier to accept.

And all that makes it easier to understand that faith and reason are not only compatible but complementary.