Faith and reason: does genuine understanding of God, soul, and evil require an antecedent act of belief, or can autonomous reason reach the same truths?

Augustine of Hippo, answered from the texts and cited to the page.

The position in brief

Faith is the prerequisite for the deepest understanding of God, soul, and evil. Isaiah 7:9 in the Old Latin translation — nisi credideritis, non intelligetis, unless you believe you will not understand — is the formula. The priority is not arbitrary fideism. The human mind is weakened by sin and bounded by its creaturely finitude; it cannot reach the highest truths by autonomous effort.

The failure of Greek philosophy on personal identity, on evil, on the love that orders the soul, is the demonstration. The Platonist books showed me much about God's nature; they could not show me Christ, and they could not give me the means to live as a creature in right relation to the Creator. Faith opens what reason then walks through; the understanding that follows faith is genuine intellectual work, not bare assent. Credo ut intelligam — I believe in order that I may understand — is anti-skeptical and anti-fideist at once.¹²

Sources

1. Thus it is said by the prophet: "Unless ye believe, ye shall not understand." Simple faith is that by which, before we attain to the height of the knowledge of the love of Christ, that we may be filled with all the fullness of God, we believe that not without reason was the dispensation of Christ's humiliation, in which He was born and suffered as man, foretold so long before by the prophets through a…

   Reply to Faustus the Manichæan, pp. 10253–10254

2. Thus it was expressly said, "Lord, show us the Father, and it sufficeth us." There only can there be security; and where security can be, there in a certain sort will be insatiable satiety. For thou wilt neither be so satiated, as to Sermon LXXVI. [CXXVI. Ben.] On the words of the Gospel, John v. 19, "The Son can do nothing of Himself, but what He seeth the Father doing." 1.

   Sermons on Selected Lessons of the New Testament, pp. 12173–12174

Where the argument is made

• On the Teacher (De Magistro, 389) on the inner Teacher who illuminates the mind from within
• Against the Academicians (Contra Academicos, 386) against the skepticism of the New Academy and the si fallor, sum anticipation of the cogito
• On Free Choice of the Will (De Libero Arbitrio, 388-395) Book II on the ascent of the mind to God by argument
• On the Usefulness of Belief (De Utilitate Credendi, 391-392)
• Soliloquies (Soliloquia, 386-387)
• Confessions Book 7 on the Platonist books and what they could and could not show me
• On Christian Doctrine (De Doctrina Christiana, 396-426)
• Isaiah 7:9 LXX in the Old Latin (nisi credideritis, non intelligetis — unless you believe, you will not understand)

How the argument was received

Defended from the early dialogues (Against the Academicians, 386) through On Christian Doctrine and the late writings. The formula became axiomatic in medieval philosophy (Anselm's fides quaerens intellectum, Aquinas's distinction of philosophy and sacred doctrine). Enlightenment rationalism rejected the priority of faith as authoritarian; the modern revival of philosophical theology (Plantinga's reformed epistemology, Catholic ressourcement, the analytical theology movement) recovers versions of the position. The fideist misreading — that I subordinate reason to bare authority — is persistent.