Summa Theologiae Moralis, vol. I: De Principiis

S. Th. II-II, q. 4, a. 8 ; De Verit., q. 10, a. 12, ad 6 ; q. 14, a. 1, ad 7.

720. Notions on certitude. — Faith is compared with intellectual habits under the respect of certitude. To understand this, it must be recalled that properly so-called or speculative certitude is the determination of the intellect to one thing, or the firm adherence of the mind to an object without fear of erring. Hence it includes a twofold element : one negative, namely the exclusion of actual doubt, the other positive, namely the firm adherence of the mind, and so certitude can be considered under a twofold respect : 1) negatively, inasmuch as it excludes all doubt or fear, and so it does not admit of degrees but consists in the indivisible ; 2) positively, inasmuch as it firmly adheres to something, and so it admits of degrees and is greater or lesser. This takes place in two ways :

a) Simply and in itself, on the part of the cause and motive, i.e. that is more certain which has a more certain cause or motive, to which error is more repugnant. And so, in this way, faith is more certain than the other intellectual habits.

Summa Theologiae Moralis I. — 36 According to the diverse motive, natural certitude is metaphysical, physical, or moral. The first rests on the essential or metaphysical necessity of things known from their very essences. The second, on their natural necessity known by induction, by which, being posited, the same cause (antecedent), even in various circumstances, always or almost always and in many cases produces the same effect (consequent), which could not be unless there were a natural property and law according to which that cause constantly tends to this effect and also, unless hindered from elsewhere, would certainly have produced it, e.g. the sun rises in the morning, from hydrogen and oxygen water is made, mothers love their children. The third rests on the testimony of other men, which is shown to be true by a kind of moral induction, because so many and so great testimonies, diverse from one another and independent, in such varied circumstances, have been given in concord, that the concord cannot be explained except by the truth of the thing asserted, e.g. the existence of Julius Caesar, Napoleon, William II, Rome.

Moreover, metaphysical certitude is greater than physical, and this greater than moral, because error about the essence of things is more repugnant than about their natural inclination, and this more than error about the testimony of others.

b) Also in a certain respect and in relation to us, i.e. on the part of the subject, that is more certain which the intellect more fully attains because it is more clearly manifested to it, and consequently that which more satisfies the intellect, in which it rests quietly and to which it adheres more intensively firmly without any possibility of doubting. In this way evident or intrinsic certitude, which necessitates the intellect, is greater than non-evident and extrinsic, which does not necessitate but is sought from the authority of others.

Moreover, there is improperly so-called, prudential or practical certitude, which excludes not every speculative doubt, but every reasonable and prudent fear of erring. This is not strict certitude because it does not exclude every fear, but it is the greatest probability which is equivalent to certitude, because it suffices for acting rightly and prudently ; whence it renders us rather morally, i.e. nearly and equally certain, than is true moral certitude. Such is, for many, the knowledge of metaphysical and essential moral truths which they admit without full evidence of them ; likewise, often, experimental certitude ; especially human faith, which does not seem easily to be able to rise to strict certitude.

721. Faith is truly certain, as is evident from the fact that it rests on the infallible truth of God revealing (Council of Trent, sess. 6, c. 9, can. 16, and Vat., sess. 3, c. 3); it is also most certain, as is held by the unanimous opinion of the Holy Fathers and Theologians.

a) But it is more certain simply and in itself, i.e. on the part of the cause and motive : for in this way faith is even more certain than metaphysical certitude, because it is more repugnant to admit the false on account of the truth of God in the light of divine grace than on account of any other motive, even on account of the full evidence of the natural light of our reason. Wherefore we adhere more and more firmly to the truths of faith than to others, because in faith the will moves the intellect to an estimatively firmer adherence, before every other natural cognition ; whence a man is ready to deny, as much as is possible for him, all those things which would contradict the revealed truths (1 John V, 9 ; Pius IX, enc. 9 Nov. 1846 : nothing more certain).

b) Nevertheless it is not more certain in a certain respect, namely, in relation to us, i.e. on the part of the subject, the believing man : for in this way faith, because it does not exclude involuntary doubt, is less certain than a fully evident assent which excludes all possible doubt. This however is accidental as to the motive of faith, which in itself has sufficient power to strengthen the intellect altogether, and it arises from our imperfect manner of concluding from it, and therefore faith is simply more certain.

Certitude on the part of the motive is called by theologians infallibility ; certitude on our part, indubitability.

The certitude of faith is preached in Scripture : a) a firm adherence is required (Acts II, 36 ; VIII, 37 ; Rom. IV, 3-10 ; Heb. X, 22 ; Gal. I, 8) ;

b) all doubt is reproved (Mk. XVI, 14 ; Lk. XXIV, 25) ;

c) the reason is indicated why the adherence must be firm (Acts I, 16 ff. ; Heb. X, 19 to the end of the chapter ; Gal. I, 8, 11 ; 1 John V, 9) ;

d) whence those things to which human reason seems to repugn are to be humbly admitted (Heb. XI, 1 ; 2 Tim. I, 12), and in the Athanasian Creed it is read : This is the Catholic faith, unless one believes it firmly...

722. Observations. — 1st The certitude of faith is greater on the part of the motive than the certitude of the judgment and the motives of credibility ; in this sense prop. 19 was condemned by Innocent XI : « The will cannot make the assent of faith in itself more firm than the weight of the reasons impelling to the assent of faith deserves », i.e. of the preambles because of which we judge that it is to be believed, or of the motives so remotely disposing to faith.

2° Since the conclusion is not more certain than the premises, it follows that in the opinion of Lugo, who says the act of faith is a reasoning, it cannot be explained how faith is more certain than rational cognition ; indeed, since he says (in the minor of the syllogism) that revelation is only practically certain, it would follow that faith has only a practical and improperly so-called certitude.

3° Some theologians falsely contend that divine grace partially supplies the defect of certitude on the part of the motive, and causes a firmer adherence than the proximate motive of adherence demands, on account of which we adhere and believe : for the will cannot reasonably command an adherence firmer than the motive of adherence deserves. Grace can, however, illuminate the intellect so that it may more clearly and better perceive the motives of faith and of credibility, even those which otherwise it would not perceive ; indeed it can exceptionally manifest internally a new and special motive of credibility to someone¹.