Blaise Pascal, answered from the texts and cited to the page.
The coeur is not a sentimental faculty. It is a faculty of intellectual intuition that grasps what neither demonstration nor sensation can reach: the first principles of geometry — space, time, number, movement — which geometry takes for granted and cannot prove without circularity; and, for those to whom grace has been given, the truths of faith.1
Religion is above reason, not against it: "the last step of reason is to acknowledge that there are infinitely many things that surpass it" (fr. 188). This acknowledgment is itself a rational act. What the coeur receives in matters of faith is not irrational; it is of a different order from what geometrical reason can touch, as charity is of a different order from mind.23
Principles are intuited, propositions are inferred, all with certainty, though in different ways.) And it is as useless and absurd for reason to demand from the heart proofs of her first principles, before admitting them, as it would be for the heart to demand from reason an intuition of all demonstrated propositions before accepting them.Pensées
But fancy is like, though contrary to feeling, so that we cannot distinguish between these contraries. One person says that my feeling is fancy, another that his fancy is feeling. We should have a rule. Reason offers itself; but it is pliable in every sense; and thus there is no rule. 275 Men often take their imagination for their heart; and they believe they are converted as soon as they think of being converted.Pensées
Without that we should weary of them. So, without the hunger for spiritual things, we weary of them. Hunger after righteousness, the eighth beatitude. 265 Faith indeed tells what the senses do not tell, but not the contrary of what they see. It is above them and not contrary to them.Pensées
The irrationalism charge has been standard since Voltaire. It rests on a confusion: I do not say that faith is contrary to reason but that it is above it, and I say this from a position in which scientific reason is taken with full seriousness — the same author who formulated the rules for affirming and denying a scientific proposition (Father Noël letter, 1647) says that the last step of reason is to acknowledge its own limits. Kołakowski (1995) correctly identifies an ambiguity: "heart" names both the natural intuition of geometric first principles (available to all) and the supernatural faculty of faith (available only to the elect). The Pensées do not fully resolve this ambiguity, because the apology was never completed. I hold the tension as the texts hold it.