Summa summae S. Thomae, Tomus III

I answer. So far is faith from excluding natural reason that it rather elevates it, illumines it, and strengthens it.

Proof. Faith could not exclude natural reason unless it were contrary to reason and impeded its exercise. Yet faith is in no wise contrary to reason; on the contrary, a perfect analogy exists between the two; nor does faith impede the exercise of reason, but, like a higher light, it merely adds strength to reason by elevating it, illumining it, and strengthening it. Therefore it does not exclude it.

Both parts of the minor were expounded and demonstrated more decisively and more clearly by the Vatican Synod, in the constitution Dei Filius, chapter 4, on Faith and Reason: « This perpetual consent of the Catholic Church has held and holds that there is a twofold order of cognition, distinct not only in its principle but also in its object: in its principle, indeed, because in the one we know by natural reason, in the other by divine faith; in its object, moreover, because besides those things to which natural reason can attain, there are proposed to us for belief mysteries hidden in God, which, unless divinely revealed, cannot become known. Wherefore the Apostle, who testifies that God was known by the nations through the things that are made, yet discoursing of the grace and truth which came by Jesus Christ, Ioann., I, 17, pronounces: We speak the wisdom of God in a mystery, a wisdom which is hidden, which God foreordained before the ages unto our glory, which none of the princes of this world knew..., but God hath revealed to us by his Spirit; for the Spirit searches all things, yea, even the deep things of God, I Cor., II, 7-10. And the Only-begotten himself confesses to the Father: Thou hast hidden these things from the wise and prudent, and hast revealed them to little ones.

And indeed reason, when illumined by faith, if it seek earnestly, piously, and soberly, attains, with God granting, some understanding of the mysteries, and that most fruitful, partly from the analogy of those things which it knows naturally, partly from the connection of the mysteries themselves with one another and with the last end of man; yet never does it become capable of perceiving them in the manner of the truths which constitute its own proper object. For the divine mysteries of their very nature so far exceed created intellect that, even though handed down by revelation and received by faith, they nevertheless remain covered by the veil of faith itself and wrapped in a kind of obscurity, so long as in this mortal life we are pilgrims away from the Lord; for we walk by faith, and not by sight, II Cor., V, 6 and 7.

But although faith is above reason, there can nevertheless never be any true dissension between faith and reason, since the same God who reveals the mysteries and infuses faith has implanted in the human mind the light of reason; and God cannot deny himself, nor can truth ever contradict truth¹. The vain show of such contradiction arises chiefly from this, that either the dogmas of faith have not been understood and set forth according to the mind of the Church, or the figments of opinions are taken for utterances of reason. We therefore define that every assertion contrary to the truth of enlightened faith is altogether false. Moreover, the Church, which together with her apostolic office of teaching has received the charge of guarding the deposit of faith, holds by divine right also the right and duty of forbidding knowledge falsely so called, lest anyone be cheated by philosophy and vain deceit, Coloss., II, 8. Wherefore all Christian faithful are forbidden not only to defend as legitimate conclusions of science opinions of this kind which are known to be contrary to the doctrine of faith, especially if they have been reproved by the Church, but they are rather bound to hold them altogether as errors which bear before themselves a fallacious appearance of truth.

Not only can faith and reason never be at variance with each other, but they also render each other mutual aid: right reason demonstrates the foundations of the faith, and, illumined by its light, cultivates the science of divine things; faith, in turn, sets reason free from errors and protects it, and furnishes it with manifold knowledge. Wherefore so far is the Church from opposing the cultivation of human arts and disciplines that she aids and promotes it in many ways. For she neither ignores nor despises the advantages which flow from them to the life of men; nay, she confesses that, as they have issued from God, the Lord of sciences, so, if they be rightly pursued, they lead back to God, his grace helping. Nor does she indeed forbid these disciplines to use within their own sphere each its own principles and its own method; but acknowledging this just liberty, she diligently takes care lest, by withstanding divine doctrine, they take upon themselves errors, or, transgressing their proper limits, occupy and disturb the things that are of faith.

For the doctrine of faith which God has revealed has not been proposed to human minds to be perfected like a philosophical invention, but has been delivered to the Spouse of Christ as a divine deposit, to be faithfully guarded and infallibly declared. Hence also that sense of the sacred dogmas must forever be retained which holy Mother Church has once declared, nor must one ever depart from that sense under the specious name and pretext of a higher understanding. Let understanding, science, and wisdom therefore increase and progress greatly and vigorously in individuals and in all, in one man and in the whole Church, through the steps of the ages and centuries: but only in their own kind, namely, in the same dogma, the same sense, and the same opinion². »

The Angelic Doctor had demonstrated this analogy and concord of faith with natural reason in I Contra gentes, cap. 7|summa-contra-gentiles-liber-primus:liber.1/capitulum.7 : « Nothing, he says, that is instilled into the soul of the disciple by the teacher contains the knowledge of the teacher, unless he teach deceitfully; which it is impious to say of God. Now the knowledge of principles naturally known has been divinely implanted in us, since God himself is the author of our nature. These principles, therefore, divine wisdom also contains. Whatever, therefore, is contrary to principles of this kind is contrary to divine wisdom. It cannot, therefore, be from God. Those things, therefore, which are held by faith from divine revelation cannot be contrary to natural knowledge... From which it is evidently gathered that, whatever arguments are brought against the documents of faith, these do not proceed rightly from principles implanted in nature and self-evident in themselves. Hence they have not the force of demonstration, but are either probable reasons or sophistical, and thus room is left for answering them. »

Concerning the relations of faith with natural reason, the aforementioned Vatican Synod published the following canons. On faith: 1. « If anyone shall say that human reason is so independent that faith cannot be commanded to it by God: let him be anathema. » — 2. « If anyone shall say that divine faith is not distinguished from natural knowledge concerning God and moral things, and that consequently for divine faith it is not required that the revealed truth be believed on account of the authority of God who reveals it: let him be anathema. » — On faith and reason: 1. « If anyone shall say that in divine revelation there are contained no true and properly so called mysteries, but that all the dogmas of faith can be understood and demonstrated from natural principles by reason duly cultivated: let him be anathema. » — 2. « If anyone shall say that the human disciplines are to be treated with such liberty that their assertions, even though they be opposed to revealed doctrine, are to be retained as true, and cannot be proscribed by the Church: let him be anathema. » — 3. « If anyone shall say that it can happen that at some time, according to the progress of science, another sense is to be attributed to the dogmas proposed by the Church than that which the Church understood and understands: let him be anathema. »

That it may be found with what great solicitude the Catholic Church has always watched over the defense of the dignity and rights of human reason, it will help to add here the four propositions by which the excessive ardor of certain men was repressed, who, in favor of faith, had depressed reason too much. Drawn up by the sacred Congregation of the Index on June 11, 1835, they were approved on the 15th of the same month by Pius IX, who ordered them published.

1° « Although faith is above reason, nevertheless no true dissent, no discord between the two can ever be found, since both arise from one and the same unchangeable source of truth, God best and greatest, and thus render each other mutual aid. » — From the Encyclical of Pius IX, November 9, 1846.

2° Reasoning can prove with certainty the existence of God, the spirituality of the soul, and the liberty of man. Faith is subsequent to revelation, and consequently it cannot fitly be alleged to prove the existence of God against the atheist, or to prove the spirituality and liberty of the rational soul against the follower of naturalism and fatalism. » — Subscribed by D. Bautain, September 8, 1840.

3° « The use of reason precedes faith, and leads man to it by the aid of revelation and grace. » Subscribed by the same, on the same day.

4° « The method which D. Thomas, D. Bonaventura, and other scholastics after them made use of does not lead to rationalism, nor was it the cause why philosophy in the schools of today ran headlong into naturalism and pantheism. Consequently it is not lawful to bring into accusation those doctors and masters for having employed this method, especially with the approbation, or at least the tacit consent, of the Church. » — This proposition is opposed to divers propositions professed by D. Bonnetty.

Whoever desires more concerning the relations of reason with faith, let him consult Fr. Perrone, Praelect. theol., De analogia rationis cum fide.]