QuestionsShould we believe without proof?Faith cannot contradict reason
Should we believe without proof?Faith and reason agree

Faith cannot contradict reason

Thomas Aquinas 1225 · 1274Faith and reason cannot contradict each other.
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What it claims

Faith cannot contradict reason. An argument against faith must be badly built, and reason can refute it.

Why

Reason and faith both tell what is true, and two truths cannot contradict each other.

In short

"Faith cannot contradict reason" is an argument by Thomas Aquinas (Summa contra Gentiles, I, 7) on the question "Should we believe without proof?" (answer: faith and reason agree). Its claim: Faith cannot contradict reason. An argument against faith must be badly built, and reason can refute it. According to AskPhilosophy's logic check (Z3 solver), the conclusion does follow from its 3 premises. AskPhilosophy presents 3 objections, 1 of them with a documented reply, and the original text behind each premise, checked word for word.

Summa contra Gentiles, I, 7
Valid

In the 13th century, the rediscovery of Aristotle caused alarm: would philosophy destroy faith? Aquinas answers with a very short argument. If both are true, they cannot contradict each other.

P1The principles reason knows naturally are true, so much so that we cannot even think them false.
P2What faith teaches is true, because God revealed it and confirmed it plainly.
P3Only the false is opposed to the true: two truths cannot contradict each other.
Therefore faith cannot contradict reason. An argument against faith must be badly built, and reason can refute it.

click a premise to reject it

If you accept every premise, logic forces you to accept the conclusion. So the debate is about the premises.
Checked by a logic solver: the premises cannot all be true while the conclusion is false.
Valid, with no hidden premise. All the weight rests on P2: an unbeliever does not grant that faith is true, and the argument does not prove it to them. Aquinas knows this: he does not claim to prove faith by reason, only to show that no demonstration can refute it. He adds a second argument: God is the author of our reason, so he cannot teach us the opposite of what he put there.
Analogy. Two maps of the same territory, drawn by the same mapmaker, cannot contradict each other. If they seem to, one has been misread. But one must first be sure both maps come from the same mapmaker: that is the question of P2.

Objections

3

Each objection is a conversation: click to see who replies and where the debate stands.

Objection anticipated by Aquinas (Summa contra Gentiles, I, 6) attacks premise 2

How do we know faith comes from God? Is believing what reason cannot check not believing lightly, as one believes fables?

Thomas d'Aquin replies
summary: their text is not yet in our corpus
Thomas d'Aquin
Believers do not believe lightly: God confirmed what exceeds reason by visible works beyond the power of all nature (healings, raisings of the dead), and by the swift conversion of a vast crowd, without weapons or promises of pleasure.
Hume 1748 · attacks premise 2

Testimony is never enough to prove a miracle so as to found a religion: it is always more likely that the witnesses are mistaken or deceiving. The confirmation invoked in P2 therefore fails.

no reply
No reply possible: objection raised in 1748, after the author's death (1274).
T
The "Latin Averroists" (Siger of Brabant) 1270 · attacks premise 3

Reason, following Aristotle, necessarily concludes some things faith denies, for instance that the world is eternal or that all humans share one intellect. One must then admit that philosophy and faith can reach opposite conclusions. Their opponents accused them of defending a "double truth".

no reply
summary: their text is not yet in our corpus
Thomas d'Aquin did reply, but that text is not yet in our corpus.