Objection 1. It would seem that something false can come under faith. For faith is condivided with hope and charity. Now something false can come under hope, since many hope to have eternal life, who will not obtain it. The same may be said of charity, for many are loved as being good, who, nevertheless, are not good. Therefore something false can be the object of faith.
Objection 2. Further, Abraham believed that Christ would be born, according to John 8:56: "Abraham your father rejoiced that he might see My day: he saw it, and was glad." But after the time of Abraham, God might not have taken flesh, for it was merely because He willed that He did, so that what Abraham believed about Christ would have been false. Therefore the object of faith can be something false.
Objection 3. Further, the ancients believed in the future birth of Christ, and many continued so to believe, until they heard the preaching of the Gospel. Now, when once Christ was born, even before He began to preach, it was false that Christ was yet to be born. Therefore something false can come under faith.
Objection 4. Further, it is a matter of faith, that one should believe that the true Body of Christ is contained in the Sacrament of the altar. But it might happen that the bread was not rightly consecrated, and that there was not Christ's true Body there, but only bread. Therefore something false can come under faith.
On the contrary, No virtue that perfects the intellect is related to the false, considered as the evil of the intellect, as the Philosopher declares (Ethic. vi, 2). Now faith is a virtue that perfects the intellect, as we shall show further on (4, 2,5). Therefore nothing false can come under it.
I answer that, Nothing comes under any power, habit or act, except by means of the formal aspect of the object: thus color cannot be seen except by means of light, and a conclusion cannot be known save through the mean of demonstration. Now it has been stated (1) that the formal aspect of the object of faith is the First Truth; so that nothing can come under faith, save in so far as it stands under the First Truth, under which nothing false can stand, as neither can non-being stand under being, nor evil under goodness. It follows therefore that nothing false can come under faith.
Reply to Objection 1. Since the true is the good of the intellect, but not of the appetitive power, it follows that all virtues which perfect the intellect, exclude the false altogether, because it belongs to the nature of a virtue to bear relation to the good alone. On the other hand those virtues which perfect the appetitive faculty, do not entirely exclude the false, for it is possible to act in accordance with justice or temperance, while having a false opinion about what one is doing. Therefore, as faith perfects the intellect, whereas hope and charity perfect the appetitive part, the comparison between them fails.
Nevertheless neither can anything false come under hope, for a man hopes to obtain eternal life, not by his own power (since this would be an act of presumption), but with the help of grace; and if he perseveres therein he will obtain eternal life surely and infallibly.
In like manner it belongs to charity to love God, wherever He may be; so that it matters not to charity, whether God be in the individual whom we love for God's sake.
Reply to Objection 2. That "God would not take flesh," considered in itself was possible even after Abraham's time, but in so far as it stands in God's foreknowledge, it has a certain necessity of infallibility, as explained in I, 14, 13 and 15: and it is thus that it comes under faith. Hence in so far as it comes under faith, it cannot be false.
Reply to Objection 3. After Christ's birth, to believe in Him, was to believe in Christ's birth at some time or other. The fixing of the time, wherein some were deceived was not due to their faith, but to a human conjecture. For it is possible for a believer to have a false opinion through a human conjecture, but it is quite impossible for a false opinion to be the outcome of faith.
Reply to Objection 4. The faith of the believer is not directed to such and such accidents of bread, but to the fact that the true body of Christ is under the appearances of sensible bread, when it is rightly consecrated. Hence if it be not rightly consecrated, it does not follow that anything false comes under faith.
Source: Summa Theologica (New Advent)