We proceed to the third article thus:
1. It seems that what is false can be held in faith. Faith is condivided with hope and charity. Now what is false can be hoped for, since many hope for eternal life although they will not attain it. In regard to charity, similarly, many are loved as if they were good although they are not good. Hence what is false can similarly be held in faith.
2. Again, Abraham believed that Christ would be born, according to John 8:56: "Your father Abraham rejoiced to see my day; and he saw it, and was glad." But after Abraham's time it was possible that God should not become incarnate, since he was incarnate purely by reason of God's will. What Abraham believed about Christ would then have been false. Hence it is possible that what is false should be held in faith.
3. Again, those of old believed that Christ would be born in the future, and many continued to believe this until the time when the Gospel was proclaimed. But after Christ had been born, and before the proclamation began, it was false that Christ would be born in the future. Hence what is false can be held in faith.
4. Again, it is one of the things pertaining to faith, that a man should believe that the true body of Christ is contained in the sacrament of the altar. Yet it might happen that the true body of Christ was not present, but only the bread, if it had not been properly consecrated. Hence what is false can be held in faith.
On the other hand: no virtue which perfects the intellect embraces what is false, since the false is the evil of the intellect, as the philosopher says (6 Ethics 2). Now faith is a virtue which perfects the intellect, as we shall show later (Q.4, Arts.2, 5). What is false cannot therefore he held in faith.
I answer: nothing can come under any power, habit, or act, except through the medium of that which its object formally signifies. Thus colour cannot be seen except through the medium of light, and a conclusion cannot be known except through the medium of demonstration. Now we said in Art.1 that the object of faith formally signifies the first truth. Hence nothing can be held in faith except in so far as it stands under the first truth. But nothing which is false can stand under the first truth, any more than not-being can stand under being, or evil under goodness. It follows that what is false cannot be held in faith.
On the first point: the true is the good of the intellect, but not of any appetitive virtue. Hence all virtues which perfect the intellect entirely exclude the false, since it is the nature of a virtue to embrace only what is good. On the other hand, the virtues which perfect the appetitive part of the soul do not entirely exclude the false. One may act in accordance with justice and temperance even though one holds a false opinion about what one is doing. Now since faith perfects the intellect, whereas hope and charity perfect the appetitive part of the soul, we cannot argue about them in the same way. Yet neither is hope directed to what is false. For one does not hope to attain eternal life by means of one's own power (which would be presumption), but by means of the help of grace, and one will assuredly and infallibly attain it through grace, if one perseveres. Similarly, since charity loves God in whomsoever he may be, it makes no difference to charity whether God is or is not present in him who is loved for God's sake.
On the second point: considered in itself, "that God should not become incarnate" was possible even after the time of Abraham. But as we said in Pt. I, Q.14, Arts.13 and 15, the incarnation has a certain infallible necessity since it stands under the foreknowledge of God, and it is thus that it is held in faith. In so far as it is held in faith, therefore, it cannot be false.
On the third point: after Christ was born, the believer believed by faith that he would be born at some time. But it was due to human conjecture, not to faith, that there was error in the determination of the time. It is indeed possible for a believer to judge wrongly by human conjecture. But it is impossible to judge wrongly by reason of faith.
On the fourth point: by faith one does not believe that the bread is in the one state or the other, but that the true body of Christ is under the sensible appearance of the bread when it has been properly consecrated. Hence if it is not properly consecrated, nothing false is held by faith in consequence.