Faith here signifies both the complexus of revealed truths, and the subjective assent given to these truths, because of the Divine authority revealing them. Reason signifies the natural faculty of understanding, human reason, as distinct from its product, science or knowledge. The Traditionalists teach that there can be no certitude with regard to natural religious truths except from Revelation. Rationalists, on the other hand, deny that any truth can be known with certainty from Revelation. The Semi-Rationalists, while admitting Revelation, teach that natural reason can understand and demonstrate all the truths of faith after they have been revealed; and that reason and faith are perfectly independent of each other. The Church, in opposition to these assertions, teaches that reason has a place in preparing the soil in which the seed of faith will be planted.
(1) Human reason of its own natural strength can know with certainty the existence of God, many of His attributes, and the fact of Revelation. Reason must precede the exercise of faith and lead us to it. For, unless we possessed natural certitude of the existence of God, of His wisdom and veracity, and of the fact of Revelation, we could not reasonably give the certain assent of faith to revealed truths.
(2) There are some truths, the strict mysteries, e.g., the Blessed Trinity, which cannot be understood and demonstrated by reason even after their revelation, except in so far as God has revealed them. This is not surprising, when we consider the vast mysteries that present themselves to our limited intelligences in the realm of the visible universe. Man can do little more than by exhaustive patience and industry catalogue the forces that govern nature. Gravitation, magnetic attraction, electrical force, life, the nature of substance are mysteries of the natural order, which should teach natural reason to avoid dogmatism in speaking of the Divine mind and its manifestations.
(a) Reason demonstrates with certitude the preamble of faith down to the speculativepractical judgment: "all men must believe in the Christian Faith." This judgment, however, is only a disposition for faith, and not the motive principle of the act of faith. The formal motive is the authority of God revealing, who can neither deceive nor be deceived. The assent of faith, when it follows this judgment, is perfectly reasonable.
(b) Reason gathers the truths of faith into a unified body of doctrine; it proposes analogies to illustrate them, and indicates the harmony existing between them and natural truths.
Faith, on the other hand, provides a norm for reason, which safeguards it from error or releases it from error's thraldom; corroborates certain truths naturally known, e.g., the distinction between substance and accidents; opens the way to reason for the discovery of new truths, e.g., with regard to the origin of human life.