“Fideism” derives from the Latin fides (faith) and refers to the position that religious truth is known through faith alone, with reason playing little or no legitimate role. The term first appeared in theological literature in the late 18th century but has been applied retroactively to thinkers stretching back to the early church. It is almost universally used as a pejorative—a label applied to opponents rather than claimed by adherents.

Strict Fideism

The strongest form holds that reason is not merely insufficient but actively hostile to faith. Tertullian (c. 155–240) asked rhetorically, “What has Athens to do with Jerusalem?”—meaning Greek philosophy has no business in Christian theology. His statement in De Carne Christi that Christ’s death “is certain because it is impossible” captures the fideist impulse: the very absurdity of the claim validates it as divine rather than human invention.

Søren Kierkegaard (1813–1855) is the philosopher most associated with fideism, though the association requires qualification. Kierkegaard emphasized faith as passionate subjective commitment that transcends rational justification. Using Abraham’s willingness to sacrifice Isaac as his primary example, Kierkegaard argued that Abraham simultaneously believed he would kill Isaac and that through Isaac he would have innumerable descendants—an embrace of paradox that reason cannot resolve. This “leap to faith” (often misquoted as “leap of faith”) represents movement beyond what evidence can support into trust that defies logical categories. For Kierkegaard, the complacent rationalized Christianity of his Danish Lutheran context had drained faith of its existential weight.

The Catholic Response

Roman Catholicism has formally condemned fideism. Vatican I (1870) affirmed that human reason can know God’s existence with certainty apart from revelation. Thomas Aquinas’s praeambula fidei (preambles of faith) established that certain truths—God’s existence, the soul’s immortality, basic moral principles—are accessible through natural reason, preparing the ground for revealed truths that exceed reason’s capacity. Pope John Paul II’s encyclical Fides et Ratio (1998) warned against fideism’s “failure to recognize the importance of rational knowledge and philosophical discourse for the understanding of faith, indeed for the very possibility of belief in God.” In the Catholic framework, faith and reason are complementary: reason establishes what faith builds upon.

Protestant Tensions

Martin Luther’s statements cut both directions. He called reason “the greatest enemy of faith” and declared that articles of Christian faith “are in presence of reason sheerly impossible, absurd, and false.” Yet he also wrote that through faith, reason “is turned into a light in the believer and serves piety as an excellent instrument.” Reformed theology generally opposes strict fideism while acknowledging the noetic effects of sin—that human reasoning is corrupted and therefore unreliable apart from regeneration and Scripture’s corrective lens.

Contemporary evangelical apologetics strongly rejects fideism. Writers cite Hebrews 11:1’s language of “substance” and “evidence” as indicating faith has rational grounding, not that it operates despite evidence. First Peter 3:15 commands believers to “give an answer to everyone who asks you to give the reason for the hope that you have.” Isaiah 1:18 records God’s invitation: “Come now, let us reason together.” Jesus commands loving God with the mind (Matthew 22:37). Under this reading, biblical faith is trust grounded in God’s demonstrated faithfulness—not a leap into the dark but confidence based on God’s track record in history and Scripture.

The Critical Problem

The term “fideism” functions more as an accusation than a description. Nearly everyone rejects the label while accusing opponents of holding the position. Catholics charge Protestants with fideism for rejecting natural theology’s authority; Protestants charge Catholics with rationalism for elevating philosophy alongside Scripture; Reformed thinkers charge Arminians with fideism for emphasizing personal decision; Arminians charge Calvinists with it for appeals to inscrutable divine sovereignty.

The deeper confusion lies in conflating distinct claims. “Faith goes beyond what reason can prove” differs substantially from “faith contradicts reason” and differs again from “faith operates independently of evidence.” Hebrews 11 commends figures who acted on God’s promises before seeing fulfillment—but those promises came through prior divine revelation and demonstration, not from nowhere. Abraham’s faith was not groundless; it rested on God’s covenant and previous faithfulness. The “leap” was trusting that God would keep his word regarding Isaac, not believing something for which no prior basis existed.

A working definition must therefore distinguish: Is fideism the claim that (1) reason cannot prove God’s existence with certainty, (2) reason is irrelevant to faith, or (3) reason is hostile to faith? Position one is defensible and widely held. Position three is rarely defended and almost universally rejected. Position two is where the real debate lies—and where most accusations of fideism are aimed.